Styjun

I am trying to perform a custom animation in my RecyclerView using the XML property android:layoutAnimation.

The problem is: When I populate my adapter directly in the activity's onCreate(), the animation triggers normally. However, when I try to populate my recyclerView from the SwipeRefreshLayout.setOnRefreshListener the animation is not triggered correctly.

I have no idea what is wrong.

Dependencies

implementation 'androidx.recyclerview:recyclerview:1.0.0'
implementation 'androidx.cardview:cardview:1.0.0'
implementation 'com.google.android.material:material:1.1.0-alpha04'

XML files

Activity XML:

<androidx.recyclerview.widget.RecyclerView
 android:id="@+id/postListRecyclerView"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:clipToPadding="false"
 android:layoutAnimation="@anim/layout_animation_enter_up"
 android:paddingTop="8dp"
 android:paddingBottom="8dp" />

layout_animation_enter_up.xml:

<layoutAnimation
 xmlns:android="http://schemas.android.com/apk/res/android"
 android:animation="@anim/item_animation_enter_up"
 android:animationOrder="normal"
 android:delay="15%" />

item_animation_enter_up.xml:

<set xmlns:android="http://schemas.android.com/apk/res/android"
 android:duration="600">

 <translate
 android:fromYDelta="50%p"
 android:interpolator="@android:anim/decelerate_interpolator"
 android:toYDelta="0" />

 <alpha
 android:fromAlpha="0"
 android:interpolator="@android:anim/decelerate_interpolator"
 android:toAlpha="1" />

</set>

My Code in simplified version

This code triggers the layout_animation_enter_up animation correctly:

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

 val adapter = PostsAdapter()
 postListRecyclerView.adapter = adapter
 val dummyData = Post(1, "Title", "Body", 1, "Name")
 val postList = listOf(dummyData, dummyData, dummyData, dummyData, dummyData, dummyData, dummyData)

 adapter.submitList(postList)

This code does not trigger the layout_animation_enter_up animation:

override fun onCreate(savedInstanceState: Bundle?) 
 postListSwipeRefreshLayout.setOnRefreshListener 
 val adapter = PostsAdapter()
 postListRecyclerView.adapter = adapter
 val dummyData = Post(1, "Title", "Body", 1, "Name")
 val postList = listOf(dummyData, dummyData, dummyData, dummyData, dummyData, dummyData, dummyData)

 adapter.submitList(postList)
 

In both code snippets (that are basically the same), I am considering that the RecyclerView is going from an empty state to a populated state. Is there any difference on the UI perspective if I populate my adapter inside the setOnRefreshListener callback or inside the onCreate?

Edit: The snippets above are different from the original codebase just to make the explanation easier. I don't want to know about performance in this question. I would like to know why the animation does not work in the second snippet and works fine in the first snippet.

Basically the first snippet only should work if you submit your list inside refresh, i.e:

postListSwipeRefreshLayout.setOnRefreshListener 
 adapter.submitList(postList)

And the second snippet of code should not trigger animation, because every time you refresh layout you create a new adapter instance which make the adapter can't observer the changes.

I don't know why you're creating a new instance every time you refresh your layout, however this consuming memory with useless instances.

In Summary: You should create instances one time only, and reuse it as much as you can instead of creating new one.