ClickDrawable.kt

class ClickDrawable(layers: Array<out Drawable> = arrayOf()) : LayerDrawable(layers) {

    private var wasPressed = false
    private var mActive = false
    private var canStart = true
    private var mBounds = bounds

    override fun isStateful(): Boolean {
        return true
    }

    override fun onStateChange(state: IntArray?): Boolean {
        val stateSet = state?.toSet() ?: emptySet()

        var enabled = false
        var pressed = false

        for (s in stateSet) {
            when (s) {
                android.R.attr.state_enabled -> enabled = true
                android.R.attr.state_pressed -> pressed = true
            }
        }

        setClickActive(enabled && wasPressed && !pressed)

        wasPressed = pressed
        return super.onStateChange(state)
    }

    private fun setClickActive(active: Boolean) {
        if (mActive != active) {
            mActive = active
            if (active && canStart) {
                canStart = false
                mBounds = copyBounds()
                startAnimation()
            }
        }
    }

    private fun setBounds(value: Float) {
        if (value == 1f) {
            canStart = true
        }
        val x = mBounds.width()
        val y = mBounds.height()
        val factorX = (x * value).roundToInt()
        val factorY = (y * value).roundToInt()
        bounds = mBounds.run {
            Rect(
                right - factorX,
                bottom - factorY,
                factorX,
                factorY
            )
        }
        invalidateSelf()
    }

    private fun startAnimation() {
        val anim = ObjectAnimator.ofFloat(this, "bounds", 0.99f, 0.95f, 1f)
        anim.duration = 225
        anim.interpolator = LinearInterpolator()
        anim.start()
    }
}