Handling touch events in a ViewGrouptakes special care, because it's common for a ViewGroupto have children that are targets for different touch events than the ViewGroup itself. To make sure that each view correctly receives the touch events intended for it, override the onInterceptTouchEvent()method. Refer to the following related resources: ●Input Events API Guide ●Sensors Overview ●Making the View Interactive

Intercept touch events in a ViewGroup

The onInterceptTouchEvent() method is called whenever a touch event is detected on the surface of a ViewGroup, including on the surface of its children. If onInterceptTouchEvent() returns true, the MotionEventis intercepted, meaning it is not passed on to the child, but rather to the onTouchEvent() method of the parent. The onInterceptTouchEvent() method gives a parent the chance to see any touch event before its children do. If you return truefrom onInterceptTouchEvent(), the child view that was previously handling touch events receives an ACTION_CANCEL, and the events from that point forward are sent to the parent's onTouchEvent() method for the usual handling. onInterceptTouchEvent() can also return falseand simply spy on events as they travel down the view hierarchy to their usual targets, which will handle the events with their own onTouchEvent(). In the following snippet, the class MyViewGroupextends ViewGroup. MyViewGroup contains multiple child views. If you drag your finger across a child view horizontally, the child view should no longer get touch events, and MyViewGroup should handle touch events by scrolling its contents. However, if you press buttons in the child view, or scroll the child view vertically, the parent shouldn't intercept those touch events, because the child is the intended target. In those cases, onInterceptTouchEvent() should return false, and MyViewGroup's onTouchEvent() won't be called.

Kotlin

class MyViewGroup @JvmOverloads constructor(
        context: Context,
        private val mTouchSlop: Int = ViewConfiguration.get(context).scaledTouchSlop
) : ViewGroup(context) {

    ...

    override fun onInterceptTouchEvent(ev: MotionEvent): Boolean {
        /*
         * This method JUST determines whether we want to intercept the motion.
         * If we return true, onTouchEvent will be called and we do the actual
         * scrolling there.
         */
        return when (ev.actionMasked) {
            // Always handle the case of the touch gesture being complete.
            MotionEvent.ACTION_CANCEL, MotionEvent.ACTION_UP -> {
                // Release the scroll.
                mIsScrolling = false
                false // Do not intercept touch event, let the child handle it
            }
            MotionEvent.ACTION_MOVE -> {
                if (mIsScrolling) {
                    // We're currently scrolling, so yes, intercept the
                    // touch event!
                    true
                } else {

                    // If the user has dragged her finger horizontally more than
                    // the touch slop, start the scroll

                    // left as an exercise for the reader
                    val xDiff: Int = calculateDistanceX(ev)

                    // Touch slop should be calculated using ViewConfiguration
                    // constants.
                    if (xDiff > mTouchSlop) {
                        // Start scrolling!
                        mIsScrolling = true
                        true
                    } else {
                        false
                    }
                }
            }
            ...
            else -> {
                // In general, we don't want to intercept touch events. They should be
                // handled by the child view.
                false
            }
        }
    }

    override fun onTouchEvent(event: MotionEvent): Boolean {
        // Here we actually handle the touch event (e.g. if the action is ACTION_MOVE,
        // scroll this container).
        // This method will only be called if the touch event was intercepted in
        // onInterceptTouchEvent
        ...
    }
}

Apr	MAY	Jun
	16
2020	2021	2022

Manage touch events in a ViewGroup

Intercept touch events in a ViewGroup

Kotlin

Java

Process ACTION_OUTSIDE events

Use ViewConfiguration constants

Kotlin

Java

Extend a child view's touchable area

Kotlin

Java