How to implement shared transition element from Re

问题:

I have a pretty straightforward case. I want to implement shared element transition between an item in recyclerView and fragment. I'm using android navigation component in my app.

There is an article about shared transition on developer.android and topic on stackoverflow but this solution works only for view that located in fragment layout that starts transition and doesn't work for items from RecyclerView. Also there is a lib on github but i don't want to rely on 3rd party libs and do it by myself.

Is there some solution for this? Maybe it should work and this is just a bug? But I haven't found any information about it.

code sample:

transition start

class TransitionStartFragment: Fragment() {

override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
    return inflater.inflate(R.layout.fragment_transition_start, container, false)
    }

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    super.onViewCreated(view, savedInstanceState)
    val testData = listOf("one", "two", "three")
    val adapter = TestAdapter(testData, View.OnClickListener { transitionWithTextViewInRecyclerViewItem(it) })
    val recyclerView = view.findViewById<RecyclerView>(R.id.test_list)
    recyclerView.adapter = adapter
    val button = view.findViewById<Button>(R.id.open_transition_end_fragment)
    button.setOnClickListener { transitionWithTextViewInFragment() }
    }

private fun transitionWithTextViewInFragment(){
    val destination = TransitionStartFragmentDirections.openTransitionEndFragment()
    val extras = FragmentNavigatorExtras(transition_start_text to "transitionTextEnd")
    findNavController().navigate(destination, extras)
    }

private fun transitionWithTextViewInRecyclerViewItem(view: View){
    val destination = TransitionStartFragmentDirections.openTransitionEndFragment()
    val extras = FragmentNavigatorExtras(view to "transitionTextEnd")
    findNavController().navigate(destination, extras)
   }

}

layout

<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">

<TextView
    android:id="@+id/transition_start_text"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="transition"
    android:transitionName="transitionTextStart"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent" />

<Button
    android:id="@+id/open_transition_end_fragment"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintTop_toBottomOf="@id/transition_start_text"
    android:text="open transition end fragment" />

<androidx.recyclerview.widget.RecyclerView
    android:id="@+id/test_list"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    app:layout_constraintTop_toBottomOf="@id/open_transition_end_fragment"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager" />

adapter for recyclerView

class TestAdapter(
    private val items: List<String>,
    private val onItemClickListener: View.OnClickListener
) : RecyclerView.Adapter<TestAdapter.ViewHodler>() {

override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHodler {
    return ViewHodler(LayoutInflater.from(parent.context).inflate(R.layout.item_test, parent, false))
    }

override fun getItemCount(): Int {
    return items.size
    }

override fun onBindViewHolder(holder: ViewHodler, position: Int) {
    val item = items[position]
    holder.transitionText.text = item
    holder.itemView.setOnClickListener { onItemClickListener.onClick(holder.transitionText) }

    }

class ViewHodler(itemView: View) : RecyclerView.ViewHolder(itemView) {
    val transitionText = itemView.findViewById<TextView>(R.id.item_test_text)
    }
}

in onItemClick I pass the textView form item in recyclerView for transition

transition end

class TransitionEndFragment : Fragment() {

override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
    setUpTransition()
    return inflater.inflate(R.layout.fragment_transition_end, container, false)
    }

private fun setUpTransition(){
    sharedElementEnterTransition = TransitionInflater.from(context).inflateTransition(android.R.transition.move)

    }
}

layout

<androidx.constraintlayout.widget.ConstraintLayout 
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="match_parent"
android:orientation="vertical">

<TextView
    android:id="@+id/transition_end_text"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="transition"
    android:transitionName="transitionTextEnd"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

fun transitionWithTextViewInFragment() - has transition.

fun transitionWithTextViewInRecyclerViewItem(view: View) - no transition.

回答1:

To solve the return transition problem you need to add this lines on the Source Fragment (the fragment with the recycler view) where you initialize your recycler view

// your recyclerView
recyclerView.apply {
                ...
                adapter = myAdapter
                postponeEnterTransition()
                viewTreeObserver
                    .addOnPreDrawListener {
                        startPostponedEnterTransition()
                        true
                    }
}

回答2:

Here is my example with RecyclerView that have fragment shared transition. In my adapter i am setting different transition name for each item based on position(In my example it is ImageView).

override fun onBindViewHolder(holder: ViewHolder, position: Int) {
    val item = items[position]
    holder.itemView.txtView.text=item
    ViewCompat.setTransitionName(holder.itemView.imgViewIcon, "Test_$position")
    holder.setClickListener(object : ViewHolder.ClickListener {
        override fun onClick(v: View, position: Int) {
            when (v.id) {
                R.id.linearLayout -> listener.onClick(item, holder.itemView.imgViewIcon, position)
            }
        }
    })

}

And when clicking on item, my interface that implemented in source fragment:

override fun onClick(text: String, img: ImageView, position: Int) {
    val action = MainFragmentDirections.actionMainFragmentToSecondFragment(text, position)
    val extras = FragmentNavigator.Extras.Builder()
            .addSharedElement(img, ViewCompat.getTransitionName(img)!!)
            .build()
    NavHostFragment.findNavController(this@MainFragment).navigate(action, extras)
}

And in my destination fragment:

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    info("onCreate")
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
        sharedElementEnterTransition = TransitionInflater.from(context).inflateTransition(android.R.transition.move)
    }
}

override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
    info("onCreateView")
    return inflater.inflate(R.layout.fragment_second, container, false)
}

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    super.onViewCreated(view, savedInstanceState)
    info("onViewCreated")
    val name=SecondFragmentArgs.fromBundle(arguments).name
    val position=SecondFragmentArgs.fromBundle(arguments).position
    txtViewName.text=name
    ViewCompat.setTransitionName(imgViewSecond, "Test_$position")
}

回答3:

Faced the same issue as many on SO with the return transition but for me the root cause of the problem was that Navigation currently only uses replace for fragment transactions and it caused my recycler in the start fragment to reload every time you hit back which was a problem by itself.

So by solving the second (root) problem the return transition started to work without delayed animations. For those of you who are looking to keep the initial state when hitting back here is what I did :

just adding a simple check in onCreateView as so

private lateinit var binding: FragmentSearchResultsBinding

override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        return if (::binding.isInitialized) {
            binding.root
        } else {
            binding = DataBindingUtil.inflate(inflater, R.layout.fragment_search_results, container, false)

            with(binding) {
                //doing some stuff here
                root
            }
        }

So triple win here: recycler is not redrawn, no refetching from server and also return transitions are working as expected.