AutoTransition not working in Motion layout

Question

I currently learning motionlayout. I created a small app in which the image in the center rotates for 5 seconds. onClick and onSwipe attributes are working fine on the device but with autotransition = animateToEnd nothing is happening when I run the app on the device. Basically I want my transition to happen automatically as the activity starts. Here is my motion layout file:

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.motion.widget.MotionLayout 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"
    app:layoutDescription="@xml/activity_main_scene">

    <ImageView
        android:id="@+id/back"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:contentDescription="TODO"
        android:src="@drawable/background" />

    <ImageView
        android:id="@+id/moon"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:scaleType="centerCrop"
        android:src="@drawable/ic_moon"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.motion.widget.MotionLayout>

Here is my motionScene:

<?xml version="1.0" encoding="utf-8"?>
<MotionScene 
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:motion="http://schemas.android.com/apk/res-auto">

    <Transition
        motion:constraintSetEnd="@+id/end"
        motion:constraintSetStart="@id/start"
        motion:duration="5000"
        motion:autoTransition="animateToEnd">
       <KeyFrameSet>
           <KeyCycle
               motion:motionTarget="@+id/moon"
               motion:framePosition="0"
               motion:wavePeriod="2"
               motion:waveShape="sawtooth"
               android:rotation="180"
               motion:waveOffset="0" />
       </KeyFrameSet>
    </Transition>

    <ConstraintSet android:id="@+id/start">
    </ConstraintSet>

    <ConstraintSet android:id="@+id/end">
    </ConstraintSet>
</MotionScene>

If there is any alternative way to run transition with motion layout please do tell. **For running the app I used to create debug apk and then run it on my device.

Answer 1

just add

app:motionInterpolator="linear"

to the Transition tag

Answer 2

note: when the version of Constrainlayout is 2.0.0-beta6 and higher, I find some differ in MotionLayout. there is the condition that this.mCurrentTransition == transition in MotionScene#autoTransition(...). I suspect the condition filter the operation back to start.

there are two solutions. 1.Downgrade to 2.0.0-beta6 or lower. 2. control it programmatically:

motionLayout.setTransitionListener(object : TransitionAdapter() {
    override fun onTransitionCompleted(motionLayout: MotionLayout, currentId: Int) {
        super.onTransitionCompleted(motionLayout, currentId)
        if (currentId == R.id.end) {
            motionLayout.transitionToStart()
        }
    }
})