Shared element transition in Jetpack Navigation fr

问题:

I'm trying to make a transition with simple animation of shared element between Fragments. In the first fragment I have elements in RecyclerView, in second - exactly the same element (defined in separate xml layout, in the list elements are also of this type) on top and details in the rest of the view. I'm giving various transitionNames for all elements in bindViewHolder and in onCreateView of target fragment I'm reading them and set them to element I want make transition. Anyway animation is not happening and I don't have any other ideas. Here below I'm putting my code snippets from source and target fragments and list adapter:

ListAdapter:

override fun onBindViewHolder(holder: ViewHolder, position: Int) {
    val item = list[position]
    ViewCompat.setTransitionName(holder.view, item.id)
    holder.view.setOnClickListener {
        listener?.onItemSelected(item, holder.view)
    }
    ...
}

interface interactionListener {
    fun onItemSelected(item: ItemData, view: View)
}

ListFragment (Source):

override fun onItemSelected(item: ItemData, view: View) {
    val action = ListFragmentDirections.itemDetailAction(item.id)
    val extras = FragmentNavigatorExtras(view to view.transitionName)
    val data = Bundle()
    data.putString("itemId", item.id)
    findNavController().navigate(action.actionId, data, null, extras)
}

SourceFragmentLayout:

<androidx.swiperefreshlayout.widget.SwipeRefreshLayout
    android:id="@+id/pullToRefresh"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recyclerView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:listitem="@layout/item_overview_row" />
</androidx.swiperefreshlayout.widget.SwipeRefreshLayout>

DetailFragment (Target):

override fun onCreateView(
    inflater: LayoutInflater,
    container: ViewGroup?,
    savedInstanceState: Bundle?
): View? {
    val rootView = inflater.inflate(R.layout.fragment_detail, container, false)

    val itemId = ItemDetailFragmentArgs.fromBundle(arguments).itemId

    (rootView.findViewById(R.id.includeDetails) as View).transitionName = itemId

    sharedElementEnterTransition = ChangeBounds().apply {
        duration = 750
    }
    sharedElementReturnTransition= ChangeBounds().apply {
        duration = 750
    }
    return rootView
}

DetailFragmentLayout:

<include
android:id="@+id/includeDetails"
layout="@layout/item_overview_row"
android:layout_width="match_parent"
android:layout_height="wrap_content" />

ItemOverviewRowLayout (this one included as item in recyclerView and in target fragment as header):

<androidx.cardview.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:clickable="true"
android:focusable="true"
android:foreground="?android:attr/selectableItemBackground"
android:orientation="vertical" >

I made also another application using Jetpack navigation, shared elements and elements described by the same layout.xml and it's working since I'm not making transition from recyclerView to target fragment. Maybe I'm wrong here, setting the transitionName to found view in target fragment? I don't know how to make it another way, because the IDs of target included layout should be unique because of recyclerView items.

回答1:

Okay, I found that how should it looks like to have enter animation with shared element: In DetailFragment (Target) you should run postponeEnterTransition() on start onViewCreated (my code from onCreateView can be moved to onViewCreated). Now you have time to sign target view element with transitionName. After you end with loading data and view, you HAVE TO run startPostponedEnterTransition(). If you don't do it, ui would freeze, so you can't do time consuming operations between postponeEnterTransition and startPostponedEnterTransition.

Anyway, now the problem is with return transition. Because of course it's the same situation - you have to reload recyclerView before you release animation. Of course you can also use postponeEnterTransition (even if it's return transition). In my case, I have list wrapped by LiveData. In source fragment lifecycle observer is checking data. There is another challenge - how to determine if data is loaded. Theoretically with recyclerView you can use helpful inline function:

inline fun <T : View> T.afterMeasure(crossinline f: T.() -> Unit) {
viewTreeObserver.addOnGlobalLayoutListener(object : ViewTreeObserver.OnGlobalLayoutListener {
    override fun onGlobalLayout() {
        if (measuredWidth > 0 && measuredHeight > 0) {
            viewTreeObserver.removeOnGlobalLayoutListener(this)
            f()
        }
    }
})

}

...and in code where you are applying your layout manager and adapter you can use it like this:

recyclerView.afterMeasure { startPostponedEnterTransition() }

it should do the work with determine time when return animation should start (you have to be sure if transitionNames are correct in recyclerView items so transition can have target view item)