architecture-components-samples | Samples for Android Architecture Components | Architecture library

Using the newest Navigation Component with the BottomNavigationView, the NavController now saves and restores the states of tabs by default:

As part of this change, the NavigationUI methods of onNavDestinationSelected(), BottomNavigationView.setupWithNavController() and NavigationView.setupWithNavController() now automatically save and restore the state of popped destinations, enabling support for multiple back stacks without any code changes. When using Navigation with Fragments, this is the recommended way to integrate with multiple back stacks.

This is great! Now switching tabs gives you the last viewed stack.

But, if the user reselects a tab, say they've gone Home -> Detail Page A -> Detail Page B, then they select the Home tab expecting to go back to the default view, they still see Detail Page B.

It seems like part of the discussion was to handle the "reselecting a tab" behavior as mentioned in the issue tracker, but I can't figure out the recommended way for implementing this.

All that's included in the NavigationAdvancedSample is:

The Problem

I have locally-generated data that I need to display in a RecyclerView. I tried to use a custom PagingSource with PagingDataAdapter to reduce the amount of data in memory, but I get visual effects when I invalidate the data, for example if I insert or delete one item:

• when the visible items belong to 2 different "pages", many unchanged items flash as if they had been modified
• if all the visible items belong to the same page, everything is fine. Only the inserted / deleted item shows an animation.

I took an example application referenced by Google's doc (PagingSample) to test the concept. The original with Room does not show artefacts, but my modified version with custom PagingSource does.

The code generated and used by Room is too complicated to see any difference that would explain the issue.

My data must be locally-generated, I can't use Room as a work-around to display them.

My question

How can I properly define a PagingSource for my local data, and use it with PagingDataAdapter without visual glitches?

Optionally, how can I know when data is discarded (so I can discard my local data as well)?

Code excerpts and details

The full example project is hosted here: https://github.com/blueglyph/PagingSampleModified

Here is the data:

I've downloaded a repository from github and in the dependencies I've founded this

I'm using a BottomNavigationView to switch between a Home and Meetings fragment. Each time I switch between them, each Fragment is recreated. I'm using a SharedViewModel between them for a shared "meetingID" variable, but that's being destroyed and recreated along with the Fragments (aggravatingly so). I'm using Jetpack Navigation Component; I almost completely copied the Google example here. It's still not working, however.

Here's a look at my onCreate and onSupportNavigateUp:

I would like to implement a navigation logic based in the Android Navigation Component in it's more updated version (2.4.0-beta02) but I'm facing some kind of issues (or non expected behaviors) related with the Android lifeycle.

My main problem is that each time you change a tab, fragments are totally recreated which means that onCreate() method it's called every time the tab is changed. I understand that for performance reasons, fragments call onDestroyView() method each time you left the tab associated with it and then when you came back to that tab onCreateView() method will be called. Actually I don't know if my implementation of the Navigation Component and it's behavior it's correct or not and I would like to know how correctly implement it.

My actual implementation looks like this:

Gradle file:

I want to implement my custom PagedList.BoundaryCallback with coroutines, liveData and repository pattern using Paging Library 2, but I couldn't find a good example of integration of these libraries.

Even in Android official samples, they use enqueue and callbacks to perform the API request with paging 2...

I read this Medium post also but it use a coroutines scope inside the boundary callback and I think that is not a good practice.

Is there any way to achieve it? Or should I migrate to Paging 3?

I want to UnitTest my AuthRepository which is using this "flow-version" of NetworkBoundResource (find the code for that below)

My current UnitTest is green when writing it like this:

While working on my android app, I found this example on the android developer site. Specifically, I don't understand the interface UserDataSource ( in /observability) and its corresponding localUserDataSource implementation class (in /observability/persistence). This doesn't look like a repository to me, but it contains an instance to a DAO like a repository would.

1. Does this approach/pattern have a name?
2. Are there advantages and disadvantages to doing this over a repository? (It seems like its a lot of redundant code, but I don't know what I'm doing yet)
3. Should I have a repository in addition to this?

I think I'm being confused by the different ways of doing things, and seeing a different approach to what I was expecting made me wonder what I really needed (or what is correct, more extensible, etc.). Thank you so much for any light you can shine on this for me.

I am using Navigation component in my App, using google Advanced Sample(here). my problem is when going back to a fragment, the scrolling position does not lost but it rearranges items and moves highest visible items so that top of those item align to top of recyclerview. please see this:

before going to next fragment:

and after back to fragment:

this problem is matter because some times clicked item goes down and not seen until scroll down. how to prevent this behavior?

please consider:

• this problem exist if using navigation component to change fragment. if start fragment using supportFragmentManager.beginTransaction() or start another activity and then go to this fragment it is OK. but if I navigate to another fragment using navigation component this problem is exist.(maybe because of recreating fragment)

• also this problem exist if using fragment in ViewPager. i.e recyclerView is in a fragment that handle with ViewPagerAdapter and viewPager is in HomeFragment that opened with Navigation component. if recyclerView is in HomeFragment there is no problem.

• no problem with LinearLayoutManager. only with StaggeredGridLayoutManager.

• there is not difference if using ViewPager2 and also FragmentStatePagerAdapter

• I try to prevent recreate of fragment(by this solution) but not solved.

UPDATE: you can clone project with this problem from here