SlideActivity | A iOS like slide back Activity framework | iOS library

I have a main_activity with 3 different Fragment and a SlideActivity. I could make transactions among 3 fragments successfully in my MainActivity.

Now I add 1 button in the MainActivity and it will open the SlideActivity. On the SlideActivity, there are 3 buttons in the navigation bar to switch to each different fragments which I already created.

The problem is when I click the list button in the navigation, an error comes out shows that

No view found for id 0x7f080052 (com.example.learnfragment:id/fragment_container) for fragment fragment_main{e1acaf7 #0 id=0x7f080052}

It seems that it cannot find the FrameLayout ID by R.id. and I believe because the navigation buttons are in the SlideActivity and it cannot find the ID which is in the MainActivity.

But how should I do for switching back to the MainActivity as well as changing different fragment?

Here's the navigation_slide_activity.xml

So I am very new to both Java and Android and am working on an app for a project. Within the app I would like to have my own image gallery / viewer specifically for the images we will be saving with the app. As such I want to use a ViewPager to slide through the images, and have created a custom pager adapter. Here are the relevant files:

I'm trying to hide and show part of my view in my PagerAdapter item but it doesn't do anything, not GONE, VISIBLE, or INVISIBLE.