Question

Why do ViewGroup‘s only get ACTION_DOWN in the onInterceptTouchEvent? According to the docs, as long as false is returned it should receive all the event types.
http://developer.android.com/reference/android/view/ViewGroup.html#onInterceptTouchEvent%28android.view.MotionEvent%29
Point #3.

Sample code:

public class MainActivity extends Activity {

    private static final String TAG = MainActivity.class.getSimpleName();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(new Container(this));
    }

    private class Container extends LinearLayout {

        public Container(Context context) {
            super(context);
            setBackgroundColor(0xFF0000FF);
        }

        @Override
        public boolean onInterceptTouchEvent(MotionEvent ev) {
            Log.i(TAG, "onInterceptTouchEvent");
            int action = ev.getActionMasked();
            switch (action) {
            case MotionEvent.ACTION_DOWN:
                Log.i(TAG, "onInterceptTouchEvent.ACTION_DOWN");
                break;
            case MotionEvent.ACTION_MOVE:
                Log.i(TAG, "onInterceptTouchEvent.ACTION_MOVE");
                break;
            case MotionEvent.ACTION_CANCEL:
            case MotionEvent.ACTION_UP:
                Log.i(TAG, "onInterceptTouchEvent.ACTION_UP");
                break;
            }
            return super.onInterceptTouchEvent(ev);
        }
    }
}

Answer 1

I’ll answer my own question: onInterceptTouchEvent only get called if the parent has a child view which returns “true” from onTouchEvent. Once the child returns true, the parent now has a chance to intercept that event.