MovableConstraintLayout.kt

class MovableConstraintLayout @JvmOverloads constructor(
        context: Context,
        attrs: AttributeSet? = null,
        defStyleAttr: Int = 0
) : ConstraintLayout(context, attrs, defStyleAttr), GestureDetector.OnGestureListener {
    private val detector: GestureDetectorCompat = GestureDetectorCompat(context, this)

    override fun onShowPress(e: MotionEvent?) {
    }

    override fun onSingleTapUp(e: MotionEvent?): Boolean = true

    override fun onDown(e: MotionEvent?): Boolean = true

    override fun onFling(
            e1: MotionEvent?, 
            e2: MotionEvent?, 
            velocityX: Float, 
            velocityY: Float
    ): Boolean = true

    override fun onScroll(
            e1: MotionEvent?, 
            e2: MotionEvent?, 
            distanceX: Float, 
            distanceY: Float
    ): Boolean = true.also { _ ->
        if (distanceY != 0f) {
            y += -distanceY * 0.5f
        }
    }

    override fun onLongPress(e: MotionEvent?) {
    }

    private var threshold: Float = 0f

    private var initializeTop: Float = 0f

    var onOverScrollListener: (() -> Unit)? = null

    override fun onLayout(
            changed: Boolean, 
            left: Int, 
            top: Int, 
            right: Int, 
            bottom: Int
    ) {
        super.onLayout(changed, left, top, right, bottom)
        initializeTop = top.toFloat()
        threshold = (bottom - top) * 0.08f
    }

    override fun onTouchEvent(event: MotionEvent?): Boolean =
            if (detector.onTouchEvent(event)) {
                true
            } else {
                super.onTouchEvent(event)
            }.also { _ ->
                if (event?.action == MotionEvent.ACTION_UP) {
                    when {
                        y.absoluteValue > threshold -> {
                            onOverScrollListener?.invoke()
                        }
                        y != initializeTop -> {
                            ViewCompat.animate(this)
                                    .setDuration(100)
                                    .translationY(initializeTop)
                                    .start()
                        }
                    }
                }
            }
}