In Transition when Fragment Shared Element Transitions happen sometimes captureEndValues does not get called and endValues return null?

问题

I wrote a transtion that extends androidx.transition.Transtion which rotates view from start value to end value, this just an example it happens with other classes that extends Transition.

It works fine if i use TransitionManager.beginDelayedTransition() if i use the start and end values as arguments instead of endTransitionValues.

class CustomRotationTransition : Transition {

    private var startRotation: Float = 0f
    private var endRotation: Float = 0f
    var forceValues: Boolean = false

    constructor(startRotation: Float, endRotation: Float, forceValues: Boolean=false) {
        this.startRotation = startRotation
        this.endRotation = endRotation
        this.forceValues = forceValues
    }

    constructor(context: Context, attrs: AttributeSet) : super(context, attrs) {

        val a = context.obtainStyledAttributes(attrs, R.styleable.CustomRotationTransition)
        startRotation =
            a.getFloat(R.styleable.CustomRotationTransition_startRotation, startRotation)
        endRotation = a.getFloat(R.styleable.CustomRotationTransition_startRotation, endRotation)
        a.recycle()

    }

    override fun captureStartValues(transitionValues: TransitionValues) {
        if (forceValues) {
            transitionValues.values[PROPNAME_ROTATION] = startRotation
        } else {
            captureValues(transitionValues)
        }
        println("⚠️ ${this::class.java.simpleName} captureStartValues() view: ${transitionValues.view} ")
        transitionValues.values.forEach { (key, value) ->
            println("Key: $key, value: $value")
        }
    }

    override fun captureEndValues(transitionValues: TransitionValues) {
        if (forceValues) {
            transitionValues.values[PROPNAME_ROTATION] = endRotation
        } else {
            captureValues(transitionValues)
        }
        println("🔥 ${this::class.java.simpleName}  captureEndValues() view: ${transitionValues.view} ")
        transitionValues.values.forEach { (key, value) ->
            println("Key: $key, value: $value")
        }
    }

    private fun captureValues(transitionValues: TransitionValues) {
        transitionValues.values[PROPNAME_ROTATION] = transitionValues.view.rotation
    }

    override fun createAnimator(
        sceneRoot: ViewGroup,
        startValues: TransitionValues?,
        endValues: TransitionValues?
    ): Animator? {

        println("🎃 ${this::class.java.simpleName}  createAnimator() startValues: $startValues endValues: $endValues ")

        if (endValues == null || startValues == null) return null // no values

        val startRotation = startValues.values[PROPNAME_ROTATION] as Float
        val endRotation = endValues.values[PROPNAME_ROTATION] as Float

        if (startRotation == endRotation) return null // no rotation to run

        val view = startValues.view

        val propRotation =
            PropertyValuesHolder.ofFloat(PROPNAME_ROTATION, startRotation, endRotation)

        val valAnim = ValueAnimator.ofPropertyValuesHolder(propRotation)
        valAnim.addUpdateListener { valueAnimator ->
            view.pivotX = view.width / 2f
            view.pivotY = view.height / 2f
            view.rotation = valueAnimator.getAnimatedValue(PROPNAME_ROTATION) as Float
        }
        return valAnim
    }

    companion object {
        private const val PROPNAME_ROTATION = "PROPNAME_ROTATION"
    }
}

When i set this transition for exit transition on a view for instance, when a fragment transition, there is also an image for shared Transition, and other transitions work.

val slide = Slide(Gravity.TOP)
    .apply {
        duration = 3000
    }
val transitionSet = TransitionSet()

val textTransition =
    CustomRotationTransition(-360f,0f, true)
        .apply {
            addTarget(tvExitTransition)
            duration = 800
        }

transitionSet.addTransition(slide)
transitionSet.addTransition(textTransition)

exitTransition = transitionSet


I: ⚠️ CustomRotationTransition captureStartValues() view: com.google.android.material.textview.MaterialTextView{ee699a0 V.ED..... ........ 79,1544-213,1598 #7f08018c app:id/tvExitTransition} 
I: Key: PROPNAME_ROTATION, value: -360.0


I: 🎃 CustomRotationTransition  createAnimator() startValues: TransitionValues@5e18b379:
I:     view = com.google.android.material.textview.MaterialTextView{ee699a0 V.ED..... ........ 79,1544-213,1598 #7f08018c app:id/tvExitTransition}
I:     values:    android:visibilityPropagation:center: [I@e8877ad
I:     android:visibilityPropagation:visibility: 0
I:     PROPNAME_ROTATION: -360.0
I:  endValues: null

i see that captureEndValues not called, i really can't get why it does not called

来源：https://stackoverflow.com/questions/64498661/in-transition-when-fragment-shared-element-transitions-happen-sometimes-capturee

标签

android

shared-element-transition