RecyclerViewPager | A ViewPager implemention base on RecyclerView | RecyclerView library

apply from: 'buildsystem/dependencies.gradle'

buildscript {
   repositories {
      jcenter()
      mavenCentral()
      maven { url 'https://maven.fabric.io/public' }
      google()
      //maven {
      //    url 'https://maven.google.com'
      //}
    }
    dependencies {
       //Update it to the latest version: 3.1.3
       classpath 'com.android.tools.build:gradle:3.1.3' 
       classpath 'com.frogermcs.androiddevmetrics:androiddevmetrics-plugin:0.5'
       classpath 'com.google.gms:google-services:3.1.2'
       classpath 'io.fabric.tools:gradle:1.25.1'
    }
}

allprojects {
   ext {
     androidApplicationId = 'com.medikoe.connect'
     androidVersionCode = 23
     androidVersionName = "1.7.2"
     testInstrumentationRunner = "android.support.test.runner.AndroidJUnitRunner"
     testApplicationId = 'com.medikoe.test'
   }

   repositories {
     google()
     jcenter()
   }
}

task clean(type: Delete) {
    delete rootProject.buildDir
}
// Remove these lines
// repositories {
//    google()
// }

repositories {
    maven {
            url 'https://maven.google.com'
        }
    jcenter()
    // Add your other repositories here
}

repositories {
    google()
    jcenter()
    // Add your other repositories here
}

repositories {
    maven {
            url 'https://maven.google.com'
        }
    jcenter()
    // Add your other repositories here
}

repositories {
    google()
    jcenter()
    // Add your other repositories here
}

 maven { url 'https://maven.google.com' }

jcenter()

 maven { url 'https://maven.google.com' }

jcenter()

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:gravity="center"
    tools:context=".MainActivity">

    <androidx.viewpager2.widget.ViewPager2
        android:id="@+id/view_pager_2"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"/>

    <com.tbuonomo.viewpagerdotsindicator.WormDotsIndicator
        android:id="@+id/dots_indicator"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="16dp"/>

</LinearLayout>

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        setupViewPager2()
    }

    private fun setupViewPager2() {
        val viewPager2 = findViewById<ViewPager2>(R.id.view_pager_2)
        val dotsIndicator = findViewById<WormDotsIndicator>(R.id.dots_indicator)

        viewPager2.adapter = PagerAdapter(this)
        dotsIndicator.setViewPager2(viewPager2)
    }
}

class PagerAdapter(fa:FragmentActivity): FragmentStateAdapter(fa) {

    override fun getItemCount(): Int = 3

    override fun createFragment(position: Int): Fragment {
        return when(position){
            0 -> SampleFragment.newInstance("One", "desc 1")
            1 -> SampleFragment.newInstance("Two", "desc 2")
            2 -> SampleFragment.newInstance("Three", "desc 3")
            else -> throw Exception("No such position")
        }
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:gravity="center"
    tools:context=".SampleFragment">
    <TextView
        android:id="@+id/txt_header"
        tools:text="Header 1"
        android:textAlignment="center"
        android:textSize="24sp"
        android:gravity="center"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>

    <TextView
        android:id="@+id/txt_desc"
        tools:text="Desc 1"
        android:textAlignment="center"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>

</LinearLayout>

class SampleFragment : Fragment() {

    private var header: String? = null
    private var desc: String? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        arguments?.let {
            header = it.getString(ARG_Header)
            desc = it.getString(ARG_Desc)
        }
    }

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        val view = inflater.inflate(R.layout.fragment_sample, container, false)
        setView(view)
        return view
    }

    private fun setView(view:View){
        val headerText = view.findViewById<TextView>(R.id.txt_header)
        headerText.text = header
        val descText = view.findViewById<TextView>(R.id.txt_desc)
        descText.text = desc

    }

    companion object {

        @JvmStatic
        fun newInstance(param1: String, param2: String) =
            SampleFragment().apply {
                arguments = Bundle().apply {
                    putString(ARG_Header, param1)
                    putString(ARG_Desc, param2)
                }
            }
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:gravity="center"
    tools:context=".MainActivity">

    <androidx.viewpager2.widget.ViewPager2
        android:id="@+id/view_pager_2"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"/>

    <com.tbuonomo.viewpagerdotsindicator.WormDotsIndicator
        android:id="@+id/dots_indicator"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="16dp"/>

</LinearLayout>

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        setupViewPager2()
    }

    private fun setupViewPager2() {
        val viewPager2 = findViewById<ViewPager2>(R.id.view_pager_2)
        val dotsIndicator = findViewById<WormDotsIndicator>(R.id.dots_indicator)

        viewPager2.adapter = PagerAdapter(this)
        dotsIndicator.setViewPager2(viewPager2)
    }
}

class PagerAdapter(fa:FragmentActivity): FragmentStateAdapter(fa) {

    override fun getItemCount(): Int = 3

    override fun createFragment(position: Int): Fragment {
        return when(position){
            0 -> SampleFragment.newInstance("One", "desc 1")
            1 -> SampleFragment.newInstance("Two", "desc 2")
            2 -> SampleFragment.newInstance("Three", "desc 3")
            else -> throw Exception("No such position")
        }
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:gravity="center"
    tools:context=".SampleFragment">
    <TextView
        android:id="@+id/txt_header"
        tools:text="Header 1"
        android:textAlignment="center"
        android:textSize="24sp"
        android:gravity="center"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>

    <TextView
        android:id="@+id/txt_desc"
        tools:text="Desc 1"
        android:textAlignment="center"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>

</LinearLayout>

class SampleFragment : Fragment() {

    private var header: String? = null
    private var desc: String? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        arguments?.let {
            header = it.getString(ARG_Header)
            desc = it.getString(ARG_Desc)
        }
    }

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        val view = inflater.inflate(R.layout.fragment_sample, container, false)
        setView(view)
        return view
    }

    private fun setView(view:View){
        val headerText = view.findViewById<TextView>(R.id.txt_header)
        headerText.text = header
        val descText = view.findViewById<TextView>(R.id.txt_desc)
        descText.text = desc

    }

    companion object {

        @JvmStatic
        fun newInstance(param1: String, param2: String) =
            SampleFragment().apply {
                arguments = Bundle().apply {
                    putString(ARG_Header, param1)
                    putString(ARG_Desc, param2)
                }
            }
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:gravity="center"
    tools:context=".MainActivity">

    <androidx.viewpager2.widget.ViewPager2
        android:id="@+id/view_pager_2"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"/>

    <com.tbuonomo.viewpagerdotsindicator.WormDotsIndicator
        android:id="@+id/dots_indicator"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="16dp"/>

</LinearLayout>

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        setupViewPager2()
    }

    private fun setupViewPager2() {
        val viewPager2 = findViewById<ViewPager2>(R.id.view_pager_2)
        val dotsIndicator = findViewById<WormDotsIndicator>(R.id.dots_indicator)

        viewPager2.adapter = PagerAdapter(this)
        dotsIndicator.setViewPager2(viewPager2)
    }
}

class PagerAdapter(fa:FragmentActivity): FragmentStateAdapter(fa) {

    override fun getItemCount(): Int = 3

    override fun createFragment(position: Int): Fragment {
        return when(position){
            0 -> SampleFragment.newInstance("One", "desc 1")
            1 -> SampleFragment.newInstance("Two", "desc 2")
            2 -> SampleFragment.newInstance("Three", "desc 3")
            else -> throw Exception("No such position")
        }
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:gravity="center"
    tools:context=".SampleFragment">
    <TextView
        android:id="@+id/txt_header"
        tools:text="Header 1"
        android:textAlignment="center"
        android:textSize="24sp"
        android:gravity="center"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>

    <TextView
        android:id="@+id/txt_desc"
        tools:text="Desc 1"
        android:textAlignment="center"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>

</LinearLayout>

class SampleFragment : Fragment() {

    private var header: String? = null
    private var desc: String? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        arguments?.let {
            header = it.getString(ARG_Header)
            desc = it.getString(ARG_Desc)
        }
    }

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        val view = inflater.inflate(R.layout.fragment_sample, container, false)
        setView(view)
        return view
    }

    private fun setView(view:View){
        val headerText = view.findViewById<TextView>(R.id.txt_header)
        headerText.text = header
        val descText = view.findViewById<TextView>(R.id.txt_desc)
        descText.text = desc

    }

    companion object {

        @JvmStatic
        fun newInstance(param1: String, param2: String) =
            SampleFragment().apply {
                arguments = Bundle().apply {
                    putString(ARG_Header, param1)
                    putString(ARG_Desc, param2)
                }
            }
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:gravity="center"
    tools:context=".MainActivity">

    <androidx.viewpager2.widget.ViewPager2
        android:id="@+id/view_pager_2"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"/>

    <com.tbuonomo.viewpagerdotsindicator.WormDotsIndicator
        android:id="@+id/dots_indicator"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="16dp"/>

</LinearLayout>

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        setupViewPager2()
    }

    private fun setupViewPager2() {
        val viewPager2 = findViewById<ViewPager2>(R.id.view_pager_2)
        val dotsIndicator = findViewById<WormDotsIndicator>(R.id.dots_indicator)

        viewPager2.adapter = PagerAdapter(this)
        dotsIndicator.setViewPager2(viewPager2)
    }
}

class PagerAdapter(fa:FragmentActivity): FragmentStateAdapter(fa) {

    override fun getItemCount(): Int = 3

    override fun createFragment(position: Int): Fragment {
        return when(position){
            0 -> SampleFragment.newInstance("One", "desc 1")
            1 -> SampleFragment.newInstance("Two", "desc 2")
            2 -> SampleFragment.newInstance("Three", "desc 3")
            else -> throw Exception("No such position")
        }
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:gravity="center"
    tools:context=".SampleFragment">
    <TextView
        android:id="@+id/txt_header"
        tools:text="Header 1"
        android:textAlignment="center"
        android:textSize="24sp"
        android:gravity="center"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>

    <TextView
        android:id="@+id/txt_desc"
        tools:text="Desc 1"
        android:textAlignment="center"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>

</LinearLayout>

class SampleFragment : Fragment() {

    private var header: String? = null
    private var desc: String? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        arguments?.let {
            header = it.getString(ARG_Header)
            desc = it.getString(ARG_Desc)
        }
    }

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        val view = inflater.inflate(R.layout.fragment_sample, container, false)
        setView(view)
        return view
    }

    private fun setView(view:View){
        val headerText = view.findViewById<TextView>(R.id.txt_header)
        headerText.text = header
        val descText = view.findViewById<TextView>(R.id.txt_desc)
        descText.text = desc

    }

    companion object {

        @JvmStatic
        fun newInstance(param1: String, param2: String) =
            SampleFragment().apply {
                arguments = Bundle().apply {
                    putString(ARG_Header, param1)
                    putString(ARG_Desc, param2)
                }
            }
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:gravity="center"
    tools:context=".MainActivity">

    <androidx.viewpager2.widget.ViewPager2
        android:id="@+id/view_pager_2"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"/>

    <com.tbuonomo.viewpagerdotsindicator.WormDotsIndicator
        android:id="@+id/dots_indicator"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="16dp"/>

</LinearLayout>

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        setupViewPager2()
    }

    private fun setupViewPager2() {
        val viewPager2 = findViewById<ViewPager2>(R.id.view_pager_2)
        val dotsIndicator = findViewById<WormDotsIndicator>(R.id.dots_indicator)

        viewPager2.adapter = PagerAdapter(this)
        dotsIndicator.setViewPager2(viewPager2)
    }
}

class PagerAdapter(fa:FragmentActivity): FragmentStateAdapter(fa) {

    override fun getItemCount(): Int = 3

    override fun createFragment(position: Int): Fragment {
        return when(position){
            0 -> SampleFragment.newInstance("One", "desc 1")
            1 -> SampleFragment.newInstance("Two", "desc 2")
            2 -> SampleFragment.newInstance("Three", "desc 3")
            else -> throw Exception("No such position")
        }
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:gravity="center"
    tools:context=".SampleFragment">
    <TextView
        android:id="@+id/txt_header"
        tools:text="Header 1"
        android:textAlignment="center"
        android:textSize="24sp"
        android:gravity="center"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>

    <TextView
        android:id="@+id/txt_desc"
        tools:text="Desc 1"
        android:textAlignment="center"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>

</LinearLayout>

class SampleFragment : Fragment() {

    private var header: String? = null
    private var desc: String? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        arguments?.let {
            header = it.getString(ARG_Header)
            desc = it.getString(ARG_Desc)
        }
    }

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        val view = inflater.inflate(R.layout.fragment_sample, container, false)
        setView(view)
        return view
    }

    private fun setView(view:View){
        val headerText = view.findViewById<TextView>(R.id.txt_header)
        headerText.text = header
        val descText = view.findViewById<TextView>(R.id.txt_desc)
        descText.text = desc

    }

    companion object {

        @JvmStatic
        fun newInstance(param1: String, param2: String) =
            SampleFragment().apply {
                arguments = Bundle().apply {
                    putString(ARG_Header, param1)
                    putString(ARG_Desc, param2)
                }
            }
    }
}

// For LinearLayoutManager horizontal orientation
recyclerView.setLayoutManager(new LinearLayoutManager(this, RecyclerView.HORIZONTAL, false));

// For GridLayoutManager vertical orientation
recyclerView.setLayoutManager(new GridLayoutManager(this, SPAN_COUNT, RecyclerView.VERTICAL, false));

SnapToBlock snapToBlock = new SnapToBlock(mMaxFlingPages);
snapToBlock.attachToRecyclerView(recyclerView);

snapToBlock.setSnapBlockCallback(new SnapToBlock.SnapBlockCallback() {
    @Override
    public void onBlockSnap(int snapPosition) {
        ...
    }

    @Override
    public void onBlockSnapped(int snapPosition) {
        ...
    }
});

/*  The number of items in the RecyclerView should be a multiple of block size; otherwise, the
    extra item views will not be positioned on a block boundary when the end of the data is reached.
    Pad out with empty item views if needed.

    Updated to accommodate RTL layouts.
 */

public class SnapToBlock extends SnapHelper {
    private RecyclerView mRecyclerView;

    // Total number of items in a block of view in the RecyclerView
    private int mBlocksize;

    // Maximum number of positions to move on a fling.
    private int mMaxPositionsToMove;

    // Width of a RecyclerView item if orientation is horizonal; height of the item if vertical
    private int mItemDimension;

    // Maxim blocks to move during most vigorous fling.
    private final int mMaxFlingBlocks;

    // Callback interface when blocks are snapped.
    private SnapBlockCallback mSnapBlockCallback;

    // When snapping, used to determine direction of snap.
    private int mPriorFirstPosition = RecyclerView.NO_POSITION;

    // Our private scroller
    private Scroller mScroller;

    // Horizontal/vertical layout helper
    private OrientationHelper mOrientationHelper;

    // LTR/RTL helper
    private LayoutDirectionHelper mLayoutDirectionHelper;

    // Borrowed from ViewPager.java
    private static final Interpolator sInterpolator = new Interpolator() {
        public float getInterpolation(float t) {
            // _o(t) = t * t * ((tension + 1) * t + tension)
            // o(t) = _o(t - 1) + 1
            t -= 1.0f;
            return t * t * t + 1.0f;
        }
    };

    SnapToBlock(int maxFlingBlocks) {
        super();
        mMaxFlingBlocks = maxFlingBlocks;
    }

    @Override
    public void attachToRecyclerView(@Nullable final RecyclerView recyclerView)
        throws IllegalStateException {

        if (recyclerView != null) {
            mRecyclerView = recyclerView;
            final LinearLayoutManager layoutManager =
                (LinearLayoutManager) recyclerView.getLayoutManager();
            if (layoutManager.canScrollHorizontally()) {
                mOrientationHelper = OrientationHelper.createHorizontalHelper(layoutManager);
                mLayoutDirectionHelper =
                    new LayoutDirectionHelper(ViewCompat.getLayoutDirection(mRecyclerView));
            } else if (layoutManager.canScrollVertically()) {
                mOrientationHelper = OrientationHelper.createVerticalHelper(layoutManager);
                // RTL doesn't matter for vertical scrolling for this class.
                mLayoutDirectionHelper = new LayoutDirectionHelper(RecyclerView.LAYOUT_DIRECTION_LTR);
            } else {
                throw new IllegalStateException("RecyclerView must be scrollable");
            }
            mScroller = new Scroller(mRecyclerView.getContext(), sInterpolator);
            initItemDimensionIfNeeded(layoutManager);
        }
        super.attachToRecyclerView(recyclerView);
    }

    // Called when the target view is available and we need to know how much more
    // to scroll to get it lined up with the side of the RecyclerView.
    @NonNull
    @Override
    public int[] calculateDistanceToFinalSnap(@NonNull RecyclerView.LayoutManager layoutManager,
                                              @NonNull View targetView) {
        int[] out = new int[2];

        if (layoutManager.canScrollHorizontally()) {
            out[0] = mLayoutDirectionHelper.getScrollToAlignView(targetView);
        }
        if (layoutManager.canScrollVertically()) {
            out[1] = mLayoutDirectionHelper.getScrollToAlignView(targetView);
        }
        if (mSnapBlockCallback != null) {
            if (out[0] == 0 && out[1] == 0) {
                mSnapBlockCallback.onBlockSnapped(layoutManager.getPosition(targetView));
            } else {
                mSnapBlockCallback.onBlockSnap(layoutManager.getPosition(targetView));
            }
        }
        return out;
    }

    // We are flinging and need to know where we are heading.
    @Override
    public int findTargetSnapPosition(RecyclerView.LayoutManager layoutManager,
                                      int velocityX, int velocityY) {
        LinearLayoutManager lm = (LinearLayoutManager) layoutManager;

        initItemDimensionIfNeeded(layoutManager);
        mScroller.fling(0, 0, velocityX, velocityY, Integer.MIN_VALUE, Integer.MAX_VALUE,
                        Integer.MIN_VALUE, Integer.MAX_VALUE);

        if (velocityX != 0) {
            return mLayoutDirectionHelper
                .getPositionsToMove(lm, mScroller.getFinalX(), mItemDimension);
        }

        if (velocityY != 0) {
            return mLayoutDirectionHelper
                .getPositionsToMove(lm, mScroller.getFinalY(), mItemDimension);
        }

        return RecyclerView.NO_POSITION;
    }

    // We have scrolled to the neighborhood where we will snap. Determine the snap position.
    @Override
    public View findSnapView(RecyclerView.LayoutManager layoutManager) {
        // Snap to a view that is either 1) toward the bottom of the data and therefore on screen,
        // or, 2) toward the top of the data and may be off-screen.
        int snapPos = calcTargetPosition((LinearLayoutManager) layoutManager);
        View snapView = (snapPos == RecyclerView.NO_POSITION)
            ? null : layoutManager.findViewByPosition(snapPos);

        if (snapView == null) {
            Log.d(TAG, "<<<<findSnapView is returning null!");
        }
        Log.d(TAG, "<<<<findSnapView snapos=" + snapPos);
        return snapView;
    }

    // Does the heavy lifting for findSnapView.
    private int calcTargetPosition(LinearLayoutManager layoutManager) {
        int snapPos;
        int firstVisiblePos = layoutManager.findFirstVisibleItemPosition();

        if (firstVisiblePos == RecyclerView.NO_POSITION) {
            return RecyclerView.NO_POSITION;
        }
        initItemDimensionIfNeeded(layoutManager);
        if (firstVisiblePos >= mPriorFirstPosition) {
            // Scrolling toward bottom of data
            int firstCompletePosition = layoutManager.findFirstCompletelyVisibleItemPosition();
            if (firstCompletePosition != RecyclerView.NO_POSITION
                && firstCompletePosition % mBlocksize == 0) {
                snapPos = firstCompletePosition;
            } else {
                snapPos = roundDownToBlockSize(firstVisiblePos + mBlocksize);
            }
        } else {
            // Scrolling toward top of data
            snapPos = roundDownToBlockSize(firstVisiblePos);
            // Check to see if target view exists. If it doesn't, force a smooth scroll.
            // SnapHelper only snaps to existing views and will not scroll to a non-existant one.
            // If limiting fling to single block, then the following is not needed since the
            // views are likely to be in the RecyclerView pool.
            if (layoutManager.findViewByPosition(snapPos) == null) {
                int[] toScroll = mLayoutDirectionHelper.calculateDistanceToScroll(layoutManager, snapPos);
                mRecyclerView.smoothScrollBy(toScroll[0], toScroll[1], sInterpolator);
            }
        }
        mPriorFirstPosition = firstVisiblePos;

        return snapPos;
    }

    private void initItemDimensionIfNeeded(final RecyclerView.LayoutManager layoutManager) {
        if (mItemDimension != 0) {
            return;
        }

        View child;
        if ((child = layoutManager.getChildAt(0)) == null) {
            return;
        }

        if (layoutManager.canScrollHorizontally()) {
            mItemDimension = child.getWidth();
            mBlocksize = getSpanCount(layoutManager) * (mRecyclerView.getWidth() / mItemDimension);
        } else if (layoutManager.canScrollVertically()) {
            mItemDimension = child.getHeight();
            mBlocksize = getSpanCount(layoutManager) * (mRecyclerView.getHeight() / mItemDimension);
        }
        mMaxPositionsToMove = mBlocksize * mMaxFlingBlocks;
    }

    private int getSpanCount(RecyclerView.LayoutManager layoutManager) {
        return (layoutManager instanceof GridLayoutManager)
            ? ((GridLayoutManager) layoutManager).getSpanCount()
            : 1;
    }

    private int roundDownToBlockSize(int trialPosition) {
        return trialPosition - trialPosition % mBlocksize;
    }

    private int roundUpToBlockSize(int trialPosition) {
        return roundDownToBlockSize(trialPosition + mBlocksize - 1);
    }

    @Nullable
    protected LinearSmoothScroller createScroller(RecyclerView.LayoutManager layoutManager) {
        if (!(layoutManager instanceof RecyclerView.SmoothScroller.ScrollVectorProvider)) {
            return null;
        }
        return new LinearSmoothScroller(mRecyclerView.getContext()) {
            @Override
            protected void onTargetFound(View targetView, RecyclerView.State state, Action action) {
                int[] snapDistances = calculateDistanceToFinalSnap(mRecyclerView.getLayoutManager(),
                                                                   targetView);
                final int dx = snapDistances[0];
                final int dy = snapDistances[1];
                final int time = calculateTimeForDeceleration(Math.max(Math.abs(dx), Math.abs(dy)));
                if (time > 0) {
                    action.update(dx, dy, time, sInterpolator);
                }
            }

            @Override
            protected float calculateSpeedPerPixel(DisplayMetrics displayMetrics) {
                return MILLISECONDS_PER_INCH / displayMetrics.densityDpi;
            }
        };
    }

    public void setSnapBlockCallback(@Nullable SnapBlockCallback callback) {
        mSnapBlockCallback = callback;
    }

    /*
        Helper class that handles calculations for LTR and RTL layouts.
     */
    private class LayoutDirectionHelper {

        // Is the layout an RTL one?
        private final boolean mIsRTL;

        @TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR1)
        LayoutDirectionHelper(int direction) {
            mIsRTL = direction == View.LAYOUT_DIRECTION_RTL;
        }

        /*
            Calculate the amount of scroll needed to align the target view with the layout edge.
         */
        int getScrollToAlignView(View targetView) {
            return (mIsRTL)
                ? mOrientationHelper.getDecoratedEnd(targetView) - mRecyclerView.getWidth()
                : mOrientationHelper.getDecoratedStart(targetView);
        }

        /**
         * Calculate the distance to final snap position when the view corresponding to the snap
         * position is not currently available.
         *
         * @param layoutManager LinearLayoutManager or descendent class
         * @param targetPos     - Adapter position to snap to
         * @return int[2] {x-distance in pixels, y-distance in pixels}
         */
        int[] calculateDistanceToScroll(LinearLayoutManager layoutManager, int targetPos) {
            int[] out = new int[2];

            int firstVisiblePos;

            firstVisiblePos = layoutManager.findFirstVisibleItemPosition();
            if (layoutManager.canScrollHorizontally()) {
                if (targetPos <= firstVisiblePos) { // scrolling toward top of data
                    if (mIsRTL) {
                        View lastView = layoutManager.findViewByPosition(layoutManager.findLastVisibleItemPosition());
                        out[0] = mOrientationHelper.getDecoratedEnd(lastView)
                            + (firstVisiblePos - targetPos) * mItemDimension;
                    } else {
                        View firstView = layoutManager.findViewByPosition(firstVisiblePos);
                        out[0] = mOrientationHelper.getDecoratedStart(firstView)
                            - (firstVisiblePos - targetPos) * mItemDimension;
                    }
                }
            }
            if (layoutManager.canScrollVertically()) {
                if (targetPos <= firstVisiblePos) { // scrolling toward top of data
                    View firstView = layoutManager.findViewByPosition(firstVisiblePos);
                    out[1] = firstView.getTop() - (firstVisiblePos - targetPos) * mItemDimension;
                }
            }

            return out;
        }

        /*
            Calculate the number of positions to move in the RecyclerView given a scroll amount
            and the size of the items to be scrolled. Return integral multiple of mBlockSize not
            equal to zero.
         */
        int getPositionsToMove(LinearLayoutManager llm, int scroll, int itemSize) {
            int positionsToMove;

            positionsToMove = roundUpToBlockSize(Math.abs(scroll) / itemSize);

            if (positionsToMove < mBlocksize) {
                // Must move at least one block
                positionsToMove = mBlocksize;
            } else if (positionsToMove > mMaxPositionsToMove) {
                // Clamp number of positions to move so we don't get wild flinging.
                positionsToMove = mMaxPositionsToMove;
            }

            if (scroll < 0) {
                positionsToMove *= -1;
            }
            if (mIsRTL) {
                positionsToMove *= -1;
            }

            if (mLayoutDirectionHelper.isDirectionToBottom(scroll < 0)) {
                // Scrolling toward the bottom of data.
                return roundDownToBlockSize(llm.findFirstVisibleItemPosition()) + positionsToMove;
            }
            // Scrolling toward the top of the data.
            return roundDownToBlockSize(llm.findLastVisibleItemPosition()) + positionsToMove;
        }

        boolean isDirectionToBottom(boolean velocityNegative) {
            //noinspection SimplifiableConditionalExpression
            return mIsRTL ? velocityNegative : !velocityNegative;
        }
    }

    public interface SnapBlockCallback {
        void onBlockSnap(int snapPosition);

        void onBlockSnapped(int snapPosition);

    }

    private static final float MILLISECONDS_PER_INCH = 100f;
    @SuppressWarnings("unused")
    private static final String TAG = "SnapToBlock";
}

// For LinearLayoutManager horizontal orientation
recyclerView.setLayoutManager(new LinearLayoutManager(this, RecyclerView.HORIZONTAL, false));

// For GridLayoutManager vertical orientation
recyclerView.setLayoutManager(new GridLayoutManager(this, SPAN_COUNT, RecyclerView.VERTICAL, false));

SnapToBlock snapToBlock = new SnapToBlock(mMaxFlingPages);
snapToBlock.attachToRecyclerView(recyclerView);

snapToBlock.setSnapBlockCallback(new SnapToBlock.SnapBlockCallback() {
    @Override
    public void onBlockSnap(int snapPosition) {
        ...
    }

    @Override
    public void onBlockSnapped(int snapPosition) {
        ...
    }
});

/*  The number of items in the RecyclerView should be a multiple of block size; otherwise, the
    extra item views will not be positioned on a block boundary when the end of the data is reached.
    Pad out with empty item views if needed.

    Updated to accommodate RTL layouts.
 */

public class SnapToBlock extends SnapHelper {
    private RecyclerView mRecyclerView;

    // Total number of items in a block of view in the RecyclerView
    private int mBlocksize;

    // Maximum number of positions to move on a fling.
    private int mMaxPositionsToMove;

    // Width of a RecyclerView item if orientation is horizonal; height of the item if vertical
    private int mItemDimension;

    // Maxim blocks to move during most vigorous fling.
    private final int mMaxFlingBlocks;

    // Callback interface when blocks are snapped.
    private SnapBlockCallback mSnapBlockCallback;

    // When snapping, used to determine direction of snap.
    private int mPriorFirstPosition = RecyclerView.NO_POSITION;

    // Our private scroller
    private Scroller mScroller;

    // Horizontal/vertical layout helper
    private OrientationHelper mOrientationHelper;

    // LTR/RTL helper
    private LayoutDirectionHelper mLayoutDirectionHelper;

    // Borrowed from ViewPager.java
    private static final Interpolator sInterpolator = new Interpolator() {
        public float getInterpolation(float t) {
            // _o(t) = t * t * ((tension + 1) * t + tension)
            // o(t) = _o(t - 1) + 1
            t -= 1.0f;
            return t * t * t + 1.0f;
        }
    };

    SnapToBlock(int maxFlingBlocks) {
        super();
        mMaxFlingBlocks = maxFlingBlocks;
    }

    @Override
    public void attachToRecyclerView(@Nullable final RecyclerView recyclerView)
        throws IllegalStateException {

        if (recyclerView != null) {
            mRecyclerView = recyclerView;
            final LinearLayoutManager layoutManager =
                (LinearLayoutManager) recyclerView.getLayoutManager();
            if (layoutManager.canScrollHorizontally()) {
                mOrientationHelper = OrientationHelper.createHorizontalHelper(layoutManager);
                mLayoutDirectionHelper =
                    new LayoutDirectionHelper(ViewCompat.getLayoutDirection(mRecyclerView));
            } else if (layoutManager.canScrollVertically()) {
                mOrientationHelper = OrientationHelper.createVerticalHelper(layoutManager);
                // RTL doesn't matter for vertical scrolling for this class.
                mLayoutDirectionHelper = new LayoutDirectionHelper(RecyclerView.LAYOUT_DIRECTION_LTR);
            } else {
                throw new IllegalStateException("RecyclerView must be scrollable");
            }
            mScroller = new Scroller(mRecyclerView.getContext(), sInterpolator);
            initItemDimensionIfNeeded(layoutManager);
        }
        super.attachToRecyclerView(recyclerView);
    }

    // Called when the target view is available and we need to know how much more
    // to scroll to get it lined up with the side of the RecyclerView.
    @NonNull
    @Override
    public int[] calculateDistanceToFinalSnap(@NonNull RecyclerView.LayoutManager layoutManager,
                                              @NonNull View targetView) {
        int[] out = new int[2];

        if (layoutManager.canScrollHorizontally()) {
            out[0] = mLayoutDirectionHelper.getScrollToAlignView(targetView);
        }
        if (layoutManager.canScrollVertically()) {
            out[1] = mLayoutDirectionHelper.getScrollToAlignView(targetView);
        }
        if (mSnapBlockCallback != null) {
            if (out[0] == 0 && out[1] == 0) {
                mSnapBlockCallback.onBlockSnapped(layoutManager.getPosition(targetView));
            } else {
                mSnapBlockCallback.onBlockSnap(layoutManager.getPosition(targetView));
            }
        }
        return out;
    }

    // We are flinging and need to know where we are heading.
    @Override
    public int findTargetSnapPosition(RecyclerView.LayoutManager layoutManager,
                                      int velocityX, int velocityY) {
        LinearLayoutManager lm = (LinearLayoutManager) layoutManager;

        initItemDimensionIfNeeded(layoutManager);
        mScroller.fling(0, 0, velocityX, velocityY, Integer.MIN_VALUE, Integer.MAX_VALUE,
                        Integer.MIN_VALUE, Integer.MAX_VALUE);

        if (velocityX != 0) {
            return mLayoutDirectionHelper
                .getPositionsToMove(lm, mScroller.getFinalX(), mItemDimension);
        }

        if (velocityY != 0) {
            return mLayoutDirectionHelper
                .getPositionsToMove(lm, mScroller.getFinalY(), mItemDimension);
        }

        return RecyclerView.NO_POSITION;
    }

    // We have scrolled to the neighborhood where we will snap. Determine the snap position.
    @Override
    public View findSnapView(RecyclerView.LayoutManager layoutManager) {
        // Snap to a view that is either 1) toward the bottom of the data and therefore on screen,
        // or, 2) toward the top of the data and may be off-screen.
        int snapPos = calcTargetPosition((LinearLayoutManager) layoutManager);
        View snapView = (snapPos == RecyclerView.NO_POSITION)
            ? null : layoutManager.findViewByPosition(snapPos);

        if (snapView == null) {
            Log.d(TAG, "<<<<findSnapView is returning null!");
        }
        Log.d(TAG, "<<<<findSnapView snapos=" + snapPos);
        return snapView;
    }

    // Does the heavy lifting for findSnapView.
    private int calcTargetPosition(LinearLayoutManager layoutManager) {
        int snapPos;
        int firstVisiblePos = layoutManager.findFirstVisibleItemPosition();

        if (firstVisiblePos == RecyclerView.NO_POSITION) {
            return RecyclerView.NO_POSITION;
        }
        initItemDimensionIfNeeded(layoutManager);
        if (firstVisiblePos >= mPriorFirstPosition) {
            // Scrolling toward bottom of data
            int firstCompletePosition = layoutManager.findFirstCompletelyVisibleItemPosition();
            if (firstCompletePosition != RecyclerView.NO_POSITION
                && firstCompletePosition % mBlocksize == 0) {
                snapPos = firstCompletePosition;
            } else {
                snapPos = roundDownToBlockSize(firstVisiblePos + mBlocksize);
            }
        } else {
            // Scrolling toward top of data
            snapPos = roundDownToBlockSize(firstVisiblePos);
            // Check to see if target view exists. If it doesn't, force a smooth scroll.
            // SnapHelper only snaps to existing views and will not scroll to a non-existant one.
            // If limiting fling to single block, then the following is not needed since the
            // views are likely to be in the RecyclerView pool.
            if (layoutManager.findViewByPosition(snapPos) == null) {
                int[] toScroll = mLayoutDirectionHelper.calculateDistanceToScroll(layoutManager, snapPos);
                mRecyclerView.smoothScrollBy(toScroll[0], toScroll[1], sInterpolator);
            }
        }
        mPriorFirstPosition = firstVisiblePos;

        return snapPos;
    }

    private void initItemDimensionIfNeeded(final RecyclerView.LayoutManager layoutManager) {
        if (mItemDimension != 0) {
            return;
        }

        View child;
        if ((child = layoutManager.getChildAt(0)) == null) {
            return;
        }

        if (layoutManager.canScrollHorizontally()) {
            mItemDimension = child.getWidth();
            mBlocksize = getSpanCount(layoutManager) * (mRecyclerView.getWidth() / mItemDimension);
        } else if (layoutManager.canScrollVertically()) {
            mItemDimension = child.getHeight();
            mBlocksize = getSpanCount(layoutManager) * (mRecyclerView.getHeight() / mItemDimension);
        }
        mMaxPositionsToMove = mBlocksize * mMaxFlingBlocks;
    }

    private int getSpanCount(RecyclerView.LayoutManager layoutManager) {
        return (layoutManager instanceof GridLayoutManager)
            ? ((GridLayoutManager) layoutManager).getSpanCount()
            : 1;
    }

    private int roundDownToBlockSize(int trialPosition) {
        return trialPosition - trialPosition % mBlocksize;
    }

    private int roundUpToBlockSize(int trialPosition) {
        return roundDownToBlockSize(trialPosition + mBlocksize - 1);
    }

    @Nullable
    protected LinearSmoothScroller createScroller(RecyclerView.LayoutManager layoutManager) {
        if (!(layoutManager instanceof RecyclerView.SmoothScroller.ScrollVectorProvider)) {
            return null;
        }
        return new LinearSmoothScroller(mRecyclerView.getContext()) {
            @Override
            protected void onTargetFound(View targetView, RecyclerView.State state, Action action) {
                int[] snapDistances = calculateDistanceToFinalSnap(mRecyclerView.getLayoutManager(),
                                                                   targetView);
                final int dx = snapDistances[0];
                final int dy = snapDistances[1];
                final int time = calculateTimeForDeceleration(Math.max(Math.abs(dx), Math.abs(dy)));
                if (time > 0) {
                    action.update(dx, dy, time, sInterpolator);
                }
            }

            @Override
            protected float calculateSpeedPerPixel(DisplayMetrics displayMetrics) {
                return MILLISECONDS_PER_INCH / displayMetrics.densityDpi;
            }
        };
    }

    public void setSnapBlockCallback(@Nullable SnapBlockCallback callback) {
        mSnapBlockCallback = callback;
    }

    /*
        Helper class that handles calculations for LTR and RTL layouts.
     */
    private class LayoutDirectionHelper {

        // Is the layout an RTL one?
        private final boolean mIsRTL;

        @TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR1)
        LayoutDirectionHelper(int direction) {
            mIsRTL = direction == View.LAYOUT_DIRECTION_RTL;
        }

        /*
            Calculate the amount of scroll needed to align the target view with the layout edge.
         */
        int getScrollToAlignView(View targetView) {
            return (mIsRTL)
                ? mOrientationHelper.getDecoratedEnd(targetView) - mRecyclerView.getWidth()
                : mOrientationHelper.getDecoratedStart(targetView);
        }

        /**
         * Calculate the distance to final snap position when the view corresponding to the snap
         * position is not currently available.
         *
         * @param layoutManager LinearLayoutManager or descendent class
         * @param targetPos     - Adapter position to snap to
         * @return int[2] {x-distance in pixels, y-distance in pixels}
         */
        int[] calculateDistanceToScroll(LinearLayoutManager layoutManager, int targetPos) {
            int[] out = new int[2];

            int firstVisiblePos;

            firstVisiblePos = layoutManager.findFirstVisibleItemPosition();
            if (layoutManager.canScrollHorizontally()) {
                if (targetPos <= firstVisiblePos) { // scrolling toward top of data
                    if (mIsRTL) {
                        View lastView = layoutManager.findViewByPosition(layoutManager.findLastVisibleItemPosition());
                        out[0] = mOrientationHelper.getDecoratedEnd(lastView)
                            + (firstVisiblePos - targetPos) * mItemDimension;
                    } else {
                        View firstView = layoutManager.findViewByPosition(firstVisiblePos);
                        out[0] = mOrientationHelper.getDecoratedStart(firstView)
                            - (firstVisiblePos - targetPos) * mItemDimension;
                    }
                }
            }
            if (layoutManager.canScrollVertically()) {
                if (targetPos <= firstVisiblePos) { // scrolling toward top of data
                    View firstView = layoutManager.findViewByPosition(firstVisiblePos);
                    out[1] = firstView.getTop() - (firstVisiblePos - targetPos) * mItemDimension;
                }
            }

            return out;
        }

        /*
            Calculate the number of positions to move in the RecyclerView given a scroll amount
            and the size of the items to be scrolled. Return integral multiple of mBlockSize not
            equal to zero.
         */
        int getPositionsToMove(LinearLayoutManager llm, int scroll, int itemSize) {
            int positionsToMove;

            positionsToMove = roundUpToBlockSize(Math.abs(scroll) / itemSize);

            if (positionsToMove < mBlocksize) {
                // Must move at least one block
                positionsToMove = mBlocksize;
            } else if (positionsToMove > mMaxPositionsToMove) {
                // Clamp number of positions to move so we don't get wild flinging.
                positionsToMove = mMaxPositionsToMove;
            }

            if (scroll < 0) {
                positionsToMove *= -1;
            }
            if (mIsRTL) {
                positionsToMove *= -1;
            }

            if (mLayoutDirectionHelper.isDirectionToBottom(scroll < 0)) {
                // Scrolling toward the bottom of data.
                return roundDownToBlockSize(llm.findFirstVisibleItemPosition()) + positionsToMove;
            }
            // Scrolling toward the top of the data.
            return roundDownToBlockSize(llm.findLastVisibleItemPosition()) + positionsToMove;
        }

        boolean isDirectionToBottom(boolean velocityNegative) {
            //noinspection SimplifiableConditionalExpression
            return mIsRTL ? velocityNegative : !velocityNegative;
        }
    }

    public interface SnapBlockCallback {
        void onBlockSnap(int snapPosition);

        void onBlockSnapped(int snapPosition);

    }

    private static final float MILLISECONDS_PER_INCH = 100f;
    @SuppressWarnings("unused")
    private static final String TAG = "SnapToBlock";
}

// For LinearLayoutManager horizontal orientation
recyclerView.setLayoutManager(new LinearLayoutManager(this, RecyclerView.HORIZONTAL, false));

// For GridLayoutManager vertical orientation
recyclerView.setLayoutManager(new GridLayoutManager(this, SPAN_COUNT, RecyclerView.VERTICAL, false));

SnapToBlock snapToBlock = new SnapToBlock(mMaxFlingPages);
snapToBlock.attachToRecyclerView(recyclerView);

snapToBlock.setSnapBlockCallback(new SnapToBlock.SnapBlockCallback() {
    @Override
    public void onBlockSnap(int snapPosition) {
        ...
    }

    @Override
    public void onBlockSnapped(int snapPosition) {
        ...
    }
});

/*  The number of items in the RecyclerView should be a multiple of block size; otherwise, the
    extra item views will not be positioned on a block boundary when the end of the data is reached.
    Pad out with empty item views if needed.

    Updated to accommodate RTL layouts.
 */

public class SnapToBlock extends SnapHelper {
    private RecyclerView mRecyclerView;

    // Total number of items in a block of view in the RecyclerView
    private int mBlocksize;

    // Maximum number of positions to move on a fling.
    private int mMaxPositionsToMove;

    // Width of a RecyclerView item if orientation is horizonal; height of the item if vertical
    private int mItemDimension;

    // Maxim blocks to move during most vigorous fling.
    private final int mMaxFlingBlocks;

    // Callback interface when blocks are snapped.
    private SnapBlockCallback mSnapBlockCallback;

    // When snapping, used to determine direction of snap.
    private int mPriorFirstPosition = RecyclerView.NO_POSITION;

    // Our private scroller
    private Scroller mScroller;

    // Horizontal/vertical layout helper
    private OrientationHelper mOrientationHelper;

    // LTR/RTL helper
    private LayoutDirectionHelper mLayoutDirectionHelper;

    // Borrowed from ViewPager.java
    private static final Interpolator sInterpolator = new Interpolator() {
        public float getInterpolation(float t) {
            // _o(t) = t * t * ((tension + 1) * t + tension)
            // o(t) = _o(t - 1) + 1
            t -= 1.0f;
            return t * t * t + 1.0f;
        }
    };

    SnapToBlock(int maxFlingBlocks) {
        super();
        mMaxFlingBlocks = maxFlingBlocks;
    }

    @Override
    public void attachToRecyclerView(@Nullable final RecyclerView recyclerView)
        throws IllegalStateException {

        if (recyclerView != null) {
            mRecyclerView = recyclerView;
            final LinearLayoutManager layoutManager =
                (LinearLayoutManager) recyclerView.getLayoutManager();
            if (layoutManager.canScrollHorizontally()) {
                mOrientationHelper = OrientationHelper.createHorizontalHelper(layoutManager);
                mLayoutDirectionHelper =
                    new LayoutDirectionHelper(ViewCompat.getLayoutDirection(mRecyclerView));
            } else if (layoutManager.canScrollVertically()) {
                mOrientationHelper = OrientationHelper.createVerticalHelper(layoutManager);
                // RTL doesn't matter for vertical scrolling for this class.
                mLayoutDirectionHelper = new LayoutDirectionHelper(RecyclerView.LAYOUT_DIRECTION_LTR);
            } else {
                throw new IllegalStateException("RecyclerView must be scrollable");
            }
            mScroller = new Scroller(mRecyclerView.getContext(), sInterpolator);
            initItemDimensionIfNeeded(layoutManager);
        }
        super.attachToRecyclerView(recyclerView);
    }

    // Called when the target view is available and we need to know how much more
    // to scroll to get it lined up with the side of the RecyclerView.
    @NonNull
    @Override
    public int[] calculateDistanceToFinalSnap(@NonNull RecyclerView.LayoutManager layoutManager,
                                              @NonNull View targetView) {
        int[] out = new int[2];

        if (layoutManager.canScrollHorizontally()) {
            out[0] = mLayoutDirectionHelper.getScrollToAlignView(targetView);
        }
        if (layoutManager.canScrollVertically()) {
            out[1] = mLayoutDirectionHelper.getScrollToAlignView(targetView);
        }
        if (mSnapBlockCallback != null) {
            if (out[0] == 0 && out[1] == 0) {
                mSnapBlockCallback.onBlockSnapped(layoutManager.getPosition(targetView));
            } else {
                mSnapBlockCallback.onBlockSnap(layoutManager.getPosition(targetView));
            }
        }
        return out;
    }

    // We are flinging and need to know where we are heading.
    @Override
    public int findTargetSnapPosition(RecyclerView.LayoutManager layoutManager,
                                      int velocityX, int velocityY) {
        LinearLayoutManager lm = (LinearLayoutManager) layoutManager;

        initItemDimensionIfNeeded(layoutManager);
        mScroller.fling(0, 0, velocityX, velocityY, Integer.MIN_VALUE, Integer.MAX_VALUE,
                        Integer.MIN_VALUE, Integer.MAX_VALUE);

        if (velocityX != 0) {
            return mLayoutDirectionHelper
                .getPositionsToMove(lm, mScroller.getFinalX(), mItemDimension);
        }

        if (velocityY != 0) {
            return mLayoutDirectionHelper
                .getPositionsToMove(lm, mScroller.getFinalY(), mItemDimension);
        }

        return RecyclerView.NO_POSITION;
    }

    // We have scrolled to the neighborhood where we will snap. Determine the snap position.
    @Override
    public View findSnapView(RecyclerView.LayoutManager layoutManager) {
        // Snap to a view that is either 1) toward the bottom of the data and therefore on screen,
        // or, 2) toward the top of the data and may be off-screen.
        int snapPos = calcTargetPosition((LinearLayoutManager) layoutManager);
        View snapView = (snapPos == RecyclerView.NO_POSITION)
            ? null : layoutManager.findViewByPosition(snapPos);

        if (snapView == null) {
            Log.d(TAG, "<<<<findSnapView is returning null!");
        }
        Log.d(TAG, "<<<<findSnapView snapos=" + snapPos);
        return snapView;
    }

    // Does the heavy lifting for findSnapView.
    private int calcTargetPosition(LinearLayoutManager layoutManager) {
        int snapPos;
        int firstVisiblePos = layoutManager.findFirstVisibleItemPosition();

        if (firstVisiblePos == RecyclerView.NO_POSITION) {
            return RecyclerView.NO_POSITION;
        }
        initItemDimensionIfNeeded(layoutManager);
        if (firstVisiblePos >= mPriorFirstPosition) {
            // Scrolling toward bottom of data
            int firstCompletePosition = layoutManager.findFirstCompletelyVisibleItemPosition();
            if (firstCompletePosition != RecyclerView.NO_POSITION
                && firstCompletePosition % mBlocksize == 0) {
                snapPos = firstCompletePosition;
            } else {
                snapPos = roundDownToBlockSize(firstVisiblePos + mBlocksize);
            }
        } else {
            // Scrolling toward top of data
            snapPos = roundDownToBlockSize(firstVisiblePos);
            // Check to see if target view exists. If it doesn't, force a smooth scroll.
            // SnapHelper only snaps to existing views and will not scroll to a non-existant one.
            // If limiting fling to single block, then the following is not needed since the
            // views are likely to be in the RecyclerView pool.
            if (layoutManager.findViewByPosition(snapPos) == null) {
                int[] toScroll = mLayoutDirectionHelper.calculateDistanceToScroll(layoutManager, snapPos);
                mRecyclerView.smoothScrollBy(toScroll[0], toScroll[1], sInterpolator);
            }
        }
        mPriorFirstPosition = firstVisiblePos;

        return snapPos;
    }

    private void initItemDimensionIfNeeded(final RecyclerView.LayoutManager layoutManager) {
        if (mItemDimension != 0) {
            return;
        }

        View child;
        if ((child = layoutManager.getChildAt(0)) == null) {
            return;
        }

        if (layoutManager.canScrollHorizontally()) {
            mItemDimension = child.getWidth();
            mBlocksize = getSpanCount(layoutManager) * (mRecyclerView.getWidth() / mItemDimension);
        } else if (layoutManager.canScrollVertically()) {
            mItemDimension = child.getHeight();
            mBlocksize = getSpanCount(layoutManager) * (mRecyclerView.getHeight() / mItemDimension);
        }
        mMaxPositionsToMove = mBlocksize * mMaxFlingBlocks;
    }

    private int getSpanCount(RecyclerView.LayoutManager layoutManager) {
        return (layoutManager instanceof GridLayoutManager)
            ? ((GridLayoutManager) layoutManager).getSpanCount()
            : 1;
    }

    private int roundDownToBlockSize(int trialPosition) {
        return trialPosition - trialPosition % mBlocksize;
    }

    private int roundUpToBlockSize(int trialPosition) {
        return roundDownToBlockSize(trialPosition + mBlocksize - 1);
    }

    @Nullable
    protected LinearSmoothScroller createScroller(RecyclerView.LayoutManager layoutManager) {
        if (!(layoutManager instanceof RecyclerView.SmoothScroller.ScrollVectorProvider)) {
            return null;
        }
        return new LinearSmoothScroller(mRecyclerView.getContext()) {
            @Override
            protected void onTargetFound(View targetView, RecyclerView.State state, Action action) {
                int[] snapDistances = calculateDistanceToFinalSnap(mRecyclerView.getLayoutManager(),
                                                                   targetView);
                final int dx = snapDistances[0];
                final int dy = snapDistances[1];
                final int time = calculateTimeForDeceleration(Math.max(Math.abs(dx), Math.abs(dy)));
                if (time > 0) {
                    action.update(dx, dy, time, sInterpolator);
                }
            }

            @Override
            protected float calculateSpeedPerPixel(DisplayMetrics displayMetrics) {
                return MILLISECONDS_PER_INCH / displayMetrics.densityDpi;
            }
        };
    }

    public void setSnapBlockCallback(@Nullable SnapBlockCallback callback) {
        mSnapBlockCallback = callback;
    }

    /*
        Helper class that handles calculations for LTR and RTL layouts.
     */
    private class LayoutDirectionHelper {

        // Is the layout an RTL one?
        private final boolean mIsRTL;

        @TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR1)
        LayoutDirectionHelper(int direction) {
            mIsRTL = direction == View.LAYOUT_DIRECTION_RTL;
        }

        /*
            Calculate the amount of scroll needed to align the target view with the layout edge.
         */
        int getScrollToAlignView(View targetView) {
            return (mIsRTL)
                ? mOrientationHelper.getDecoratedEnd(targetView) - mRecyclerView.getWidth()
                : mOrientationHelper.getDecoratedStart(targetView);
        }

        /**
         * Calculate the distance to final snap position when the view corresponding to the snap
         * position is not currently available.
         *
         * @param layoutManager LinearLayoutManager or descendent class
         * @param targetPos     - Adapter position to snap to
         * @return int[2] {x-distance in pixels, y-distance in pixels}
         */
        int[] calculateDistanceToScroll(LinearLayoutManager layoutManager, int targetPos) {
            int[] out = new int[2];

            int firstVisiblePos;

            firstVisiblePos = layoutManager.findFirstVisibleItemPosition();
            if (layoutManager.canScrollHorizontally()) {
                if (targetPos <= firstVisiblePos) { // scrolling toward top of data
                    if (mIsRTL) {
                        View lastView = layoutManager.findViewByPosition(layoutManager.findLastVisibleItemPosition());
                        out[0] = mOrientationHelper.getDecoratedEnd(lastView)
                            + (firstVisiblePos - targetPos) * mItemDimension;
                    } else {
                        View firstView = layoutManager.findViewByPosition(firstVisiblePos);
                        out[0] = mOrientationHelper.getDecoratedStart(firstView)
                            - (firstVisiblePos - targetPos) * mItemDimension;
                    }
                }
            }
            if (layoutManager.canScrollVertically()) {
                if (targetPos <= firstVisiblePos) { // scrolling toward top of data
                    View firstView = layoutManager.findViewByPosition(firstVisiblePos);
                    out[1] = firstView.getTop() - (firstVisiblePos - targetPos) * mItemDimension;
                }
            }

            return out;
        }

        /*
            Calculate the number of positions to move in the RecyclerView given a scroll amount
            and the size of the items to be scrolled. Return integral multiple of mBlockSize not
            equal to zero.
         */
        int getPositionsToMove(LinearLayoutManager llm, int scroll, int itemSize) {
            int positionsToMove;

            positionsToMove = roundUpToBlockSize(Math.abs(scroll) / itemSize);

            if (positionsToMove < mBlocksize) {
                // Must move at least one block
                positionsToMove = mBlocksize;
            } else if (positionsToMove > mMaxPositionsToMove) {
                // Clamp number of positions to move so we don't get wild flinging.
                positionsToMove = mMaxPositionsToMove;
            }

            if (scroll < 0) {
                positionsToMove *= -1;
            }
            if (mIsRTL) {
                positionsToMove *= -1;
            }

            if (mLayoutDirectionHelper.isDirectionToBottom(scroll < 0)) {
                // Scrolling toward the bottom of data.
                return roundDownToBlockSize(llm.findFirstVisibleItemPosition()) + positionsToMove;
            }
            // Scrolling toward the top of the data.
            return roundDownToBlockSize(llm.findLastVisibleItemPosition()) + positionsToMove;
        }

        boolean isDirectionToBottom(boolean velocityNegative) {
            //noinspection SimplifiableConditionalExpression
            return mIsRTL ? velocityNegative : !velocityNegative;
        }
    }

    public interface SnapBlockCallback {
        void onBlockSnap(int snapPosition);

        void onBlockSnapped(int snapPosition);

    }

    private static final float MILLISECONDS_PER_INCH = 100f;
    @SuppressWarnings("unused")
    private static final String TAG = "SnapToBlock";
}

// For LinearLayoutManager horizontal orientation
recyclerView.setLayoutManager(new LinearLayoutManager(this, RecyclerView.HORIZONTAL, false));

// For GridLayoutManager vertical orientation
recyclerView.setLayoutManager(new GridLayoutManager(this, SPAN_COUNT, RecyclerView.VERTICAL, false));

SnapToBlock snapToBlock = new SnapToBlock(mMaxFlingPages);
snapToBlock.attachToRecyclerView(recyclerView);

snapToBlock.setSnapBlockCallback(new SnapToBlock.SnapBlockCallback() {
    @Override
    public void onBlockSnap(int snapPosition) {
        ...
    }

    @Override
    public void onBlockSnapped(int snapPosition) {
        ...
    }
});

/*  The number of items in the RecyclerView should be a multiple of block size; otherwise, the
    extra item views will not be positioned on a block boundary when the end of the data is reached.
    Pad out with empty item views if needed.

    Updated to accommodate RTL layouts.
 */

public class SnapToBlock extends SnapHelper {
    private RecyclerView mRecyclerView;

    // Total number of items in a block of view in the RecyclerView
    private int mBlocksize;

    // Maximum number of positions to move on a fling.
    private int mMaxPositionsToMove;

    // Width of a RecyclerView item if orientation is horizonal; height of the item if vertical
    private int mItemDimension;

    // Maxim blocks to move during most vigorous fling.
    private final int mMaxFlingBlocks;

    // Callback interface when blocks are snapped.
    private SnapBlockCallback mSnapBlockCallback;

    // When snapping, used to determine direction of snap.
    private int mPriorFirstPosition = RecyclerView.NO_POSITION;

    // Our private scroller
    private Scroller mScroller;

    // Horizontal/vertical layout helper
    private OrientationHelper mOrientationHelper;

    // LTR/RTL helper
    private LayoutDirectionHelper mLayoutDirectionHelper;

    // Borrowed from ViewPager.java
    private static final Interpolator sInterpolator = new Interpolator() {
        public float getInterpolation(float t) {
            // _o(t) = t * t * ((tension + 1) * t + tension)
            // o(t) = _o(t - 1) + 1
            t -= 1.0f;
            return t * t * t + 1.0f;
        }
    };

    SnapToBlock(int maxFlingBlocks) {
        super();
        mMaxFlingBlocks = maxFlingBlocks;
    }

    @Override
    public void attachToRecyclerView(@Nullable final RecyclerView recyclerView)
        throws IllegalStateException {

        if (recyclerView != null) {
            mRecyclerView = recyclerView;
            final LinearLayoutManager layoutManager =
                (LinearLayoutManager) recyclerView.getLayoutManager();
            if (layoutManager.canScrollHorizontally()) {
                mOrientationHelper = OrientationHelper.createHorizontalHelper(layoutManager);
                mLayoutDirectionHelper =
                    new LayoutDirectionHelper(ViewCompat.getLayoutDirection(mRecyclerView));
            } else if (layoutManager.canScrollVertically()) {
                mOrientationHelper = OrientationHelper.createVerticalHelper(layoutManager);
                // RTL doesn't matter for vertical scrolling for this class.
                mLayoutDirectionHelper = new LayoutDirectionHelper(RecyclerView.LAYOUT_DIRECTION_LTR);
            } else {
                throw new IllegalStateException("RecyclerView must be scrollable");
            }
            mScroller = new Scroller(mRecyclerView.getContext(), sInterpolator);
            initItemDimensionIfNeeded(layoutManager);
        }
        super.attachToRecyclerView(recyclerView);
    }

    // Called when the target view is available and we need to know how much more
    // to scroll to get it lined up with the side of the RecyclerView.
    @NonNull
    @Override
    public int[] calculateDistanceToFinalSnap(@NonNull RecyclerView.LayoutManager layoutManager,
                                              @NonNull View targetView) {
        int[] out = new int[2];

        if (layoutManager.canScrollHorizontally()) {
            out[0] = mLayoutDirectionHelper.getScrollToAlignView(targetView);
        }
        if (layoutManager.canScrollVertically()) {
            out[1] = mLayoutDirectionHelper.getScrollToAlignView(targetView);
        }
        if (mSnapBlockCallback != null) {
            if (out[0] == 0 && out[1] == 0) {
                mSnapBlockCallback.onBlockSnapped(layoutManager.getPosition(targetView));
            } else {
                mSnapBlockCallback.onBlockSnap(layoutManager.getPosition(targetView));
            }
        }
        return out;
    }

    // We are flinging and need to know where we are heading.
    @Override
    public int findTargetSnapPosition(RecyclerView.LayoutManager layoutManager,
                                      int velocityX, int velocityY) {
        LinearLayoutManager lm = (LinearLayoutManager) layoutManager;

        initItemDimensionIfNeeded(layoutManager);
        mScroller.fling(0, 0, velocityX, velocityY, Integer.MIN_VALUE, Integer.MAX_VALUE,
                        Integer.MIN_VALUE, Integer.MAX_VALUE);

        if (velocityX != 0) {
            return mLayoutDirectionHelper
                .getPositionsToMove(lm, mScroller.getFinalX(), mItemDimension);
        }

        if (velocityY != 0) {
            return mLayoutDirectionHelper
                .getPositionsToMove(lm, mScroller.getFinalY(), mItemDimension);
        }

        return RecyclerView.NO_POSITION;
    }

    // We have scrolled to the neighborhood where we will snap. Determine the snap position.
    @Override
    public View findSnapView(RecyclerView.LayoutManager layoutManager) {
        // Snap to a view that is either 1) toward the bottom of the data and therefore on screen,
        // or, 2) toward the top of the data and may be off-screen.
        int snapPos = calcTargetPosition((LinearLayoutManager) layoutManager);
        View snapView = (snapPos == RecyclerView.NO_POSITION)
            ? null : layoutManager.findViewByPosition(snapPos);

        if (snapView == null) {
            Log.d(TAG, "<<<<findSnapView is returning null!");
        }
        Log.d(TAG, "<<<<findSnapView snapos=" + snapPos);
        return snapView;
    }

    // Does the heavy lifting for findSnapView.
    private int calcTargetPosition(LinearLayoutManager layoutManager) {
        int snapPos;
        int firstVisiblePos = layoutManager.findFirstVisibleItemPosition();

        if (firstVisiblePos == RecyclerView.NO_POSITION) {
            return RecyclerView.NO_POSITION;
        }
        initItemDimensionIfNeeded(layoutManager);
        if (firstVisiblePos >= mPriorFirstPosition) {
            // Scrolling toward bottom of data
            int firstCompletePosition = layoutManager.findFirstCompletelyVisibleItemPosition();
            if (firstCompletePosition != RecyclerView.NO_POSITION
                && firstCompletePosition % mBlocksize == 0) {
                snapPos = firstCompletePosition;
            } else {
                snapPos = roundDownToBlockSize(firstVisiblePos + mBlocksize);
            }
        } else {
            // Scrolling toward top of data
            snapPos = roundDownToBlockSize(firstVisiblePos);
            // Check to see if target view exists. If it doesn't, force a smooth scroll.
            // SnapHelper only snaps to existing views and will not scroll to a non-existant one.
            // If limiting fling to single block, then the following is not needed since the
            // views are likely to be in the RecyclerView pool.
            if (layoutManager.findViewByPosition(snapPos) == null) {
                int[] toScroll = mLayoutDirectionHelper.calculateDistanceToScroll(layoutManager, snapPos);
                mRecyclerView.smoothScrollBy(toScroll[0], toScroll[1], sInterpolator);
            }
        }
        mPriorFirstPosition = firstVisiblePos;

        return snapPos;
    }

    private void initItemDimensionIfNeeded(final RecyclerView.LayoutManager layoutManager) {
        if (mItemDimension != 0) {
            return;
        }

        View child;
        if ((child = layoutManager.getChildAt(0)) == null) {
            return;
        }

        if (layoutManager.canScrollHorizontally()) {
            mItemDimension = child.getWidth();
            mBlocksize = getSpanCount(layoutManager) * (mRecyclerView.getWidth() / mItemDimension);
        } else if (layoutManager.canScrollVertically()) {
            mItemDimension = child.getHeight();
            mBlocksize = getSpanCount(layoutManager) * (mRecyclerView.getHeight() / mItemDimension);
        }
        mMaxPositionsToMove = mBlocksize * mMaxFlingBlocks;
    }

    private int getSpanCount(RecyclerView.LayoutManager layoutManager) {
        return (layoutManager instanceof GridLayoutManager)
            ? ((GridLayoutManager) layoutManager).getSpanCount()
            : 1;
    }

    private int roundDownToBlockSize(int trialPosition) {
        return trialPosition - trialPosition % mBlocksize;
    }

    private int roundUpToBlockSize(int trialPosition) {
        return roundDownToBlockSize(trialPosition + mBlocksize - 1);
    }

    @Nullable
    protected LinearSmoothScroller createScroller(RecyclerView.LayoutManager layoutManager) {
        if (!(layoutManager instanceof RecyclerView.SmoothScroller.ScrollVectorProvider)) {
            return null;
        }
        return new LinearSmoothScroller(mRecyclerView.getContext()) {
            @Override
            protected void onTargetFound(View targetView, RecyclerView.State state, Action action) {
                int[] snapDistances = calculateDistanceToFinalSnap(mRecyclerView.getLayoutManager(),
                                                                   targetView);
                final int dx = snapDistances[0];
                final int dy = snapDistances[1];
                final int time = calculateTimeForDeceleration(Math.max(Math.abs(dx), Math.abs(dy)));
                if (time > 0) {
                    action.update(dx, dy, time, sInterpolator);
                }
            }

            @Override
            protected float calculateSpeedPerPixel(DisplayMetrics displayMetrics) {
                return MILLISECONDS_PER_INCH / displayMetrics.densityDpi;
            }
        };
    }

    public void setSnapBlockCallback(@Nullable SnapBlockCallback callback) {
        mSnapBlockCallback = callback;
    }

    /*
        Helper class that handles calculations for LTR and RTL layouts.
     */
    private class LayoutDirectionHelper {

        // Is the layout an RTL one?
        private final boolean mIsRTL;

        @TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR1)
        LayoutDirectionHelper(int direction) {
            mIsRTL = direction == View.LAYOUT_DIRECTION_RTL;
        }

        /*
            Calculate the amount of scroll needed to align the target view with the layout edge.
         */
        int getScrollToAlignView(View targetView) {
            return (mIsRTL)
                ? mOrientationHelper.getDecoratedEnd(targetView) - mRecyclerView.getWidth()
                : mOrientationHelper.getDecoratedStart(targetView);
        }

        /**
         * Calculate the distance to final snap position when the view corresponding to the snap
         * position is not currently available.
         *
         * @param layoutManager LinearLayoutManager or descendent class
         * @param targetPos     - Adapter position to snap to
         * @return int[2] {x-distance in pixels, y-distance in pixels}
         */
        int[] calculateDistanceToScroll(LinearLayoutManager layoutManager, int targetPos) {
            int[] out = new int[2];

            int firstVisiblePos;

            firstVisiblePos = layoutManager.findFirstVisibleItemPosition();
            if (layoutManager.canScrollHorizontally()) {
                if (targetPos <= firstVisiblePos) { // scrolling toward top of data
                    if (mIsRTL) {
                        View lastView = layoutManager.findViewByPosition(layoutManager.findLastVisibleItemPosition());
                        out[0] = mOrientationHelper.getDecoratedEnd(lastView)
                            + (firstVisiblePos - targetPos) * mItemDimension;
                    } else {
                        View firstView = layoutManager.findViewByPosition(firstVisiblePos);
                        out[0] = mOrientationHelper.getDecoratedStart(firstView)
                            - (firstVisiblePos - targetPos) * mItemDimension;
                    }
                }
            }
            if (layoutManager.canScrollVertically()) {
                if (targetPos <= firstVisiblePos) { // scrolling toward top of data
                    View firstView = layoutManager.findViewByPosition(firstVisiblePos);
                    out[1] = firstView.getTop() - (firstVisiblePos - targetPos) * mItemDimension;
                }
            }

            return out;
        }

        /*
            Calculate the number of positions to move in the RecyclerView given a scroll amount
            and the size of the items to be scrolled. Return integral multiple of mBlockSize not
            equal to zero.
         */
        int getPositionsToMove(LinearLayoutManager llm, int scroll, int itemSize) {
            int positionsToMove;

            positionsToMove = roundUpToBlockSize(Math.abs(scroll) / itemSize);

            if (positionsToMove < mBlocksize) {
                // Must move at least one block
                positionsToMove = mBlocksize;
            } else if (positionsToMove > mMaxPositionsToMove) {
                // Clamp number of positions to move so we don't get wild flinging.
                positionsToMove = mMaxPositionsToMove;
            }

            if (scroll < 0) {
                positionsToMove *= -1;
            }
            if (mIsRTL) {
                positionsToMove *= -1;
            }

            if (mLayoutDirectionHelper.isDirectionToBottom(scroll < 0)) {
                // Scrolling toward the bottom of data.
                return roundDownToBlockSize(llm.findFirstVisibleItemPosition()) + positionsToMove;
            }
            // Scrolling toward the top of the data.
            return roundDownToBlockSize(llm.findLastVisibleItemPosition()) + positionsToMove;
        }

        boolean isDirectionToBottom(boolean velocityNegative) {
            //noinspection SimplifiableConditionalExpression
            return mIsRTL ? velocityNegative : !velocityNegative;
        }
    }

    public interface SnapBlockCallback {
        void onBlockSnap(int snapPosition);

        void onBlockSnapped(int snapPosition);

    }

    private static final float MILLISECONDS_PER_INCH = 100f;
    @SuppressWarnings("unused")
    private static final String TAG = "SnapToBlock";
}

<com.takusemba.multisnaprecyclerview.MultiSnapRecyclerView
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    app:msrv_gravity="start"
    app:msrv_snap_count="3" />

    val inflater = LayoutInflater.from(this)
    val viewPagerHolders = HashMap<Int, ViewPagerViewHolder>()
    viewPager.adapter = object : RecyclerPagerAdapter<ViewPagerViewHolder>() {

        override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewPagerViewHolder {
            return ViewPagerViewHolder(inflater.inflate(R.layout.cell, parent, false))
        }

        override fun getItemCount(): Int = 100

        override fun onBindViewHolder(holder: ViewPagerViewHolder, position: Int) {
            holder.textView.text = position.toString()
            viewPagerHolders.remove(holder.adapterPosition)
            holder.adapterPosition = position
            viewPagerHolders[position] = holder

        }
    }
    viewPager.addOnPageChangeListener(object : ViewPager.OnPageChangeListener {
        var selectedHolder: ViewPagerViewHolder? = null

        override fun onPageScrollStateChanged(state: Int) {}
        override fun onPageScrolled(position: Int, positionOffset: Float, positionOffsetPixels: Int) {}

        override fun onPageSelected(position: Int) {
            val holder = viewPagerHolders[position]
            if (holder != null) {
                if (selectedHolder != null && selectedHolder != holder)
                    selectedHolder!!.textView.text = selectedHolder!!.adapterPosition.toString()
                holder.textView.text = "selected:${position.toString()}"
                selectedHolder = holder
            }
        }
    })

class ViewPagerViewHolder(itemView: View) : RecyclerPagerAdapter.ViewHolder(itemView) {
    val textView: TextView = itemView.findViewById(android.R.id.text1)
    var adapterPosition: Int = Int.MIN_VALUE
}

    val inflater = LayoutInflater.from(this)
    val viewPagerHolders = HashMap<Int, ViewPagerViewHolder>()
    viewPager.adapter = object : RecyclerPagerAdapter<ViewPagerViewHolder>() {

        override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewPagerViewHolder {
            return ViewPagerViewHolder(inflater.inflate(R.layout.cell, parent, false))
        }

        override fun getItemCount(): Int = 100

        override fun onBindViewHolder(holder: ViewPagerViewHolder, position: Int) {
            holder.textView.text = position.toString()
            viewPagerHolders.remove(holder.adapterPosition)
            holder.adapterPosition = position
            viewPagerHolders[position] = holder

        }
    }
    viewPager.addOnPageChangeListener(object : ViewPager.OnPageChangeListener {
        var selectedHolder: ViewPagerViewHolder? = null

        override fun onPageScrollStateChanged(state: Int) {}
        override fun onPageScrolled(position: Int, positionOffset: Float, positionOffsetPixels: Int) {}

        override fun onPageSelected(position: Int) {
            val holder = viewPagerHolders[position]
            if (holder != null) {
                if (selectedHolder != null && selectedHolder != holder)
                    selectedHolder!!.textView.text = selectedHolder!!.adapterPosition.toString()
                holder.textView.text = "selected:${position.toString()}"
                selectedHolder = holder
            }
        }
    })

class ViewPagerViewHolder(itemView: View) : RecyclerPagerAdapter.ViewHolder(itemView) {
    val textView: TextView = itemView.findViewById(android.R.id.text1)
    var adapterPosition: Int = Int.MIN_VALUE
}

youTubePlayerView.initialize("YOUR API KEY",
            new YouTubePlayer.OnInitializedListener() {
                @Override
                public void onInitializationSuccess(YouTubePlayer.Provider provider,
                        YouTubePlayer youTubePlayer, boolean b) {


                    youTubePlayer.loadVideo("VIDEO_ID_HERE");
                }
                @Override
                public void onInitializationFailure(YouTubePlayer.Provider provider,
                        YouTubeInitializationResult youTubeInitializationResult) {

                }
    });

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/fragment_container"
android:layout_width="match_parent"
android:layout_height="wrap_content"/>

public RecyclerViewConstructor(Activity hostActivity) {
    super();
    this.hostActivity = hostActivity;
    lastClickTime = 0;
}

Activity host
@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    View rootView = LayoutInflater.from(mContext).inflate(R.layout.item_fragment, null);
    return new ViewHolder(rootView);
}

@Override
public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
    YourFragment yourFragment = YourFragment.newInstance();
    FragmentManager fm = hostActivity.getSupportFragmentManager();
    fm.addOnBackStackChangedListener(this);
    FragmentTransaction ft = fm.beginTransaction();
    ft.add(R.id.fragment_container, fragment, tag);
}

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/fragment_container"
android:layout_width="match_parent"
android:layout_height="wrap_content"/>

public RecyclerViewConstructor(Activity hostActivity) {
    super();
    this.hostActivity = hostActivity;
    lastClickTime = 0;
}

Activity host
@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    View rootView = LayoutInflater.from(mContext).inflate(R.layout.item_fragment, null);
    return new ViewHolder(rootView);
}

@Override
public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
    YourFragment yourFragment = YourFragment.newInstance();
    FragmentManager fm = hostActivity.getSupportFragmentManager();
    fm.addOnBackStackChangedListener(this);
    FragmentTransaction ft = fm.beginTransaction();
    ft.add(R.id.fragment_container, fragment, tag);
}

public class ViewHolderInds extends RecyclerView.ViewHolder {
...
    public final int frameId; //Unique identifier for ValueFrame
...
    public ViewHolderInds(View view) {
        super(view);
...
        frameId = view.generateViewId();
        ((FrameLayout) view.findViewById(R.id.valueFrame)).setId(frameId);
...
    }
}

    @Override
    public void onBindViewHolder(@NonNull ViewHolderInds holder, int position) {
        getActivity().getSupportFragmentManager().
                beginTransaction().
                replace(holder.frameId, EditFragment.newInstance(...)).
                commit();
...

public class ViewHolderInds extends RecyclerView.ViewHolder {
...
    public final int frameId; //Unique identifier for ValueFrame
...
    public ViewHolderInds(View view) {
        super(view);
...
        frameId = view.generateViewId();
        ((FrameLayout) view.findViewById(R.id.valueFrame)).setId(frameId);
...
    }
}

    @Override
    public void onBindViewHolder(@NonNull ViewHolderInds holder, int position) {
        getActivity().getSupportFragmentManager().
                beginTransaction().
                replace(holder.frameId, EditFragment.newInstance(...)).
                commit();
...

compile 'com.squareup.okhttp3:okhttp:3.8.1'
compile 'com.squareup.picasso:picasso:2.5.2'

android {
  configurations{
     all*.exclude module: 'okhttp'
     all*.exclude module: 'okio'
   }
}

compile 'com.squareup.okhttp3:okhttp:3.8.1'
compile 'com.squareup.picasso:picasso:2.5.2'

android {
  configurations{
     all*.exclude module: 'okhttp'
     all*.exclude module: 'okio'
   }
}

compile 'com.squareup.okhttp:okhttp:2.4.0'
compile 'com.squareup.okhttp:okhttp-urlconnection:2.2.0'

compileOptions {
    sourceCompatibility JavaVersion.VERSION_1_8
    targetCompatibility JavaVersion.VERSION_1_8
}

<ScrollView
    android:id="@+id/scrollViewDashboard"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

 new GetPlaylistAsyncTask(mYouTubeDataApi,getContext()) {
            @Override
            public void onPostExecute(Pair<String, List<Video>> result) {
                handleGetPlaylistResult(playlistVideos, result);
            }
        }.execute(playlistVideos.playlistId, playlistVideos.getNextPageToken());

 new GetPlaylistAsyncTask(mYouTubeDataApi,getContext(),YouTubeRecyclerViewFragment.this)
          .execute(playlistVideos.playlistId, playlistVideos.getNextPageToken());

    @Override
    public void handleGetPlaylistResult(PlaylistVideos playlistVideos, Pair<String, List<Video>> result) {
        if (result == null) return;
        if (playlistVideos == null){
             playlistVideos = mPlaylistVideos;
        }
        final int positionStart = playlistVideos.size();
        playlistVideos.setNextPageToken(result.first);
        playlistVideos.addAll(result.second);
        mPlaylistCardAdapter.notifyItemRangeInserted(positionStart, result.second.size());
    }

 public class GetPlaylistAsyncTask{

 private AsyncResponse theListener;

 public GetPlaylistAsyncTask(YouTube api, Context context, YouTubeRecyclerViewFragment frag ) {
    mYouTubeDataApi = api;
    mContext = context;
    theListener = (AsyncResponse)frag;
 }

 @Override
       public void onPostExecute(Pair<String, List<Video>> result) {
          progressBar.dismiss();
          theListener.handleGetPlaylistResult(null,result);
      }
}

 new GetPlaylistAsyncTask(mYouTubeDataApi,getContext()) {
            @Override
            public void onPostExecute(Pair<String, List<Video>> result) {
                handleGetPlaylistResult(playlistVideos, result);
            }
        }.execute(playlistVideos.playlistId, playlistVideos.getNextPageToken());

 new GetPlaylistAsyncTask(mYouTubeDataApi,getContext(),YouTubeRecyclerViewFragment.this)
          .execute(playlistVideos.playlistId, playlistVideos.getNextPageToken());

    @Override
    public void handleGetPlaylistResult(PlaylistVideos playlistVideos, Pair<String, List<Video>> result) {
        if (result == null) return;
        if (playlistVideos == null){
             playlistVideos = mPlaylistVideos;
        }
        final int positionStart = playlistVideos.size();
        playlistVideos.setNextPageToken(result.first);
        playlistVideos.addAll(result.second);
        mPlaylistCardAdapter.notifyItemRangeInserted(positionStart, result.second.size());
    }

 public class GetPlaylistAsyncTask{

 private AsyncResponse theListener;

 public GetPlaylistAsyncTask(YouTube api, Context context, YouTubeRecyclerViewFragment frag ) {
    mYouTubeDataApi = api;
    mContext = context;
    theListener = (AsyncResponse)frag;
 }

 @Override
       public void onPostExecute(Pair<String, List<Video>> result) {
          progressBar.dismiss();
          theListener.handleGetPlaylistResult(null,result);
      }
}

 new GetPlaylistAsyncTask(mYouTubeDataApi,getContext()) {
            @Override
            public void onPostExecute(Pair<String, List<Video>> result) {
                handleGetPlaylistResult(playlistVideos, result);
            }
        }.execute(playlistVideos.playlistId, playlistVideos.getNextPageToken());

 new GetPlaylistAsyncTask(mYouTubeDataApi,getContext(),YouTubeRecyclerViewFragment.this)
          .execute(playlistVideos.playlistId, playlistVideos.getNextPageToken());

    @Override
    public void handleGetPlaylistResult(PlaylistVideos playlistVideos, Pair<String, List<Video>> result) {
        if (result == null) return;
        if (playlistVideos == null){
             playlistVideos = mPlaylistVideos;
        }
        final int positionStart = playlistVideos.size();
        playlistVideos.setNextPageToken(result.first);
        playlistVideos.addAll(result.second);
        mPlaylistCardAdapter.notifyItemRangeInserted(positionStart, result.second.size());
    }

 public class GetPlaylistAsyncTask{

 private AsyncResponse theListener;

 public GetPlaylistAsyncTask(YouTube api, Context context, YouTubeRecyclerViewFragment frag ) {
    mYouTubeDataApi = api;
    mContext = context;
    theListener = (AsyncResponse)frag;
 }

 @Override
       public void onPostExecute(Pair<String, List<Video>> result) {
          progressBar.dismiss();
          theListener.handleGetPlaylistResult(null,result);
      }
}