TransitionListener.kt

/**
 * Helper class for [MotionLayout.TransitionListener] which provides Android Support Annotations and proper parameter names
 */
abstract class TransitionListener: MotionLayout.TransitionListener {

    /**
     * Called when a transition has been completed
     */
    override fun onTransitionCompleted(view: MotionLayout, @IdRes constraintSetId: Int) = Unit

    /**
     * Called when a [KeyTrigger] is triggered
     */
    override fun onTransitionTrigger(view: MotionLayout, @IdRes triggerId: Int, isPositive: Boolean, progress: Float) = Unit

    /**
     * Called when a transition has been started
     */
    @Deprecated("This is not being called due to a bug in MotionLayout. This will be fixed in Alpha 4 (hopefully).")
    override fun onTransitionStarted(view: MotionLayout, @IdRes startConstraintSetId: Int, @IdRes endConstraintSetId: Int) = Unit

    /**
     * Called when the transition or its progress changes
     */
    override fun onTransitionChange(view: MotionLayout, @IdRes startConstraintSetId: Int, @IdRes endConstraintSetId: Int, progress: Float) = Unit
}