Android Programming: The Big Nerd Ranch Guide, 5th Edition

Handling Touch Events

One way to listen for touch events is to set a touch event listener using the following View function:

    fun setOnTouchListener(l: View.OnTouchListener)

This function works the same way as setOnClickListener(View.OnClickListener). You provide an implementation of View.OnTouchListener, and your listener will be called every time a touch event happens.

However, because you are subclassing View, you can take a shortcut and override this View function instead:

    override fun onTouchEvent(event: MotionEvent): Boolean

This function receives an instance of MotionEvent, a class that describes the touch event, including its location and its action. The action describes the stage of the event: