淡入、淡出在MotionLayout中不起作用

<MotionScene xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:motion="http://schemas.android.com/apk/res-auto">

    <Transition
        motion:constraintSetStart="@+id/start"
        motion:constraintSetEnd="@+id/end">

        <KeyFrameSet>
            <KeyAttribute
                motion:framePosition="0"
                motion:target="@id/myView">
                <CustomAttribute
                    motion:attributeName="alpha"
                    motion:customFloatValue="0" />
            </KeyAttribute>
            <KeyAttribute
                motion:framePosition="100"
                motion:target="@id/myView">
                <CustomAttribute
                    motion:attributeName="alpha"
                    motion:customFloatValue="1" />
            </KeyAttribute>
        </KeyFrameSet>

        <OnSwipe
            motion:dragDirection="dragUp"
            motion:touchAnchorId="@id/myView"
            motion:touchAnchorSide="top" />

    </Transition>

    <ConstraintSet android:id="@+id/start">
        <Constraint android:id="@id/myView">
            <Layout
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                motion:layout_constraintTop_toTopOf="parent"
                motion:layout_constraintStart_toStartOf="parent" />
        </Constraint>
    </ConstraintSet>

    <ConstraintSet android:id="@+id/end">
        <Constraint android:id="@id/myView">
            <Layout
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                motion:layout_constraintTop_toBottomOf="parent"
                motion:layout_constraintStart_toStartOf="parent" />
        </Constraint>
    </ConstraintSet>

</MotionScene>