Aggiunta del supporto per animazioni d'indietro predittive integrate e personalizzate

If you've already migrated your app to the new system back APIs, you can opt in to predictive back to automatically receive in-app animations and also support custom transitions.

Add support for built-in in-app animations

Video: Predictive back animations

After opting in, your app displays animations for back-to-home, cross-activity, and cross-task.

You can also upgrade your material component dependency to v1.10.0 of MDC Android to receive material component animations like the following:

See the material component developer guidance on GitHub for more information.

The video shows a brief example of predictive back animations for cross-activity and back-to-home using the Android Settings app.

  1. In the animation, the user swipes back to return to the previous settings screen—an example of a cross-activity animation.
  2. Now on the previous screen, the user begins swiping back a second time, showing a preview of the home screen with its wallpaper—an example of the back-to-home animation.
  3. The user continues to swipe right, showing an animation of the window shrinking down to the icon on the home screen.
  4. The user has now fully returned to the home screen.

Read more about supporting predictive back.

Add custom in-app transitions and animations

You can create custom in-app property animations and transitions using the Progress API and custom cross-activity animations method overrideActivityTransition.

Add custom transitions using the Progress API

With AndroidX Activity 1.8.0-alpha01 or higher, you can use the Predictive Back Progress APIs to develop custom animations for the predictive back gesture in your app. Within OnBackPressedCallback we've introduced the handleOnBackProgressed, handleOnBackCancelled and handleOnBackStarted methods to animate objects while the user swipes back. Use these methods if you need something more custom than the default animations provided by the new system animations or the Material Component animations.

We expect most apps to use the backward compatible AndroidX APIs, but there are also similar platform APIs within the OnBackAnimationCallback interface available to test in Android 14 Developer Preview 1 and higher.

Use the Progress APIs with AndroidX Transitions

The Progress APIs can be used with AndroidX Transitions 1.5.0-alpha01 or higher on Android 14 and above to create Predictive Back transitions.

  1. Use TransitionManager#controlDelayedTransition instead of beginDelayedTransition to play transitions as the user swipes back.
  2. Create the transition within handleOnBackStarted.
  3. Play the transition with the back event within handleOnBackProgressed by relating currentFraction to BackEvent.progress which exposes how far the user has swiped back.
  4. Finish the transition after the user has committed the back gesture in handleOnBackPressed.
  5. Finally, reset the state of the transition within handleOnBackCancelled.

The following video, Kotlin code, and XML demonstrate a custom transition between two boxes implemented with OnBackPressedCallback:

class MyFragment : Fragment() {

    val transitionSet = TransitionSet().apply {
        addTransition(Fade(Fade.MODE_OUT))
        addTransition(ChangeBounds())
        addTransition(Fade(Fade.MODE_IN))
    }
    ...
    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)

        val callback = object : OnBackPressedCallback(enabled = false) {

            var controller: TransitionSeekController? = null

            @RequiresApi(34)
            override fun handleOnBackStarted(backEvent: BackEvent) {
                // Create the transition
                controller = TransitionManager.controlDelayedTransition(
                    binding.card,
                    transitionSet
                )
                changeTextVisibility(ShowText.SHORT)
            }

            @RequiresApi(34)
            override fun handleOnBackProgressed(backEvent: BackEvent) {
                // Play the transition as the user swipes back
                if (controller?.isReady == true) {
                    controller?.currentFraction = backEvent.progress
                }
            }

            override fun handleOnBackPressed() {
                // Finish playing the transition when the user commits back
                controller?.animateToEnd()
                this.isEnabled = false
            }

            @RequiresApi(34)
            override fun handleOnBackCancelled() {
                // If the user cancels the back gesture, reset the state
                transition(ShowText.LONG)
            }
        }

        binding.shortText.setOnClickListener {
            transition(ShowText.LONG)
            callback.isEnabled = true
        }

        this.requireActivity().onBackPressedDispatcher.addCallback(callback)
    }

    private fun transition(showText: ShowText) {
        TransitionManager.beginDelayedTransition(
            binding.card,
            transitionSet
        )
        changeTextVisibility(showText)
    }

    enum class ShowText { SHORT, LONG }
    private fun changeTextVisibility(showText: ShowText) {
        when (showText) {
            ShowText.SHORT -> {
                binding.shortText.isVisible = true
                binding.longText.isVisible = false
            }
            ShowText.LONG -> {
                binding.shortText.isVisible = false
                binding.longText.isVisible = true
            }
        }
    }
}

<?xml version="1.0" encoding="utf-8"?>
...
    <androidx.constraintlayout.widget.ConstraintLayout
        android:id="@+id/card"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        ...>

        <TextView
            android:id="@+id/short_text"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            ... />

        <TextView
            android:id="@+id/long_text"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:visibility="gone"
            .../>

    </androidx.constraintlayout.widget.ConstraintLayout>

Note the following when working with Predictive Back transitions:

  • Use isSeekingSupported to check if the transition supports Predictive Back.
  • Override isSeekingSupported to return true for your custom transitions.
  • Create one controller per animation.
  • Predictive Back transitions are supported with AndroidX transitions, but not with framework transitions. We recommend migrating away from framework transitions.
  • Predictive Back transitions are supported on Android 14+ devices and are not backward compatible.
  • Transitions created with XML scenes are also supported. In handleOnBackStarted, set your TransitionSeekController to the result of TransitionManager.createSeekController instead of the result of controlDelayedTransition.

Add custom activity transitions on Android 14 and higher

To ensure that custom Activity transitions support predictive back on Android 14 and higher, you can use overrideActivityTransition instead of overridePendingTransition. This means that the transition animation plays as the user swipes back.

To provide an example of how this might work, imagine a scenario in which Activity B is on top of Activity A in the back stack. You would handle custom Activity animations in the following way:

  • Call either opening or closing transitions within Activity B's onCreate method.
  • When the user navigates to Activity B, use OVERRIDE_TRANSITION_OPEN. When the user swipes to navigate back to Activity A, use OVERRIDE_TRANSITION_CLOSE.

  • When specifying OVERRIDE_TRANSITION_CLOSE, the enterAnim is Activity A's enter animation and the exitAnim is Activity B's exit animation.