Android - Intercept and pass on all touch events

Question

I have an overlay ViewGroup that is the size of the screen which I want to use to show an effect when the user interacts with the app, but still passes the onTouch event to any

Answer 1

The only way to build such an interceptor is using a custom ViewGroup layout.

But implementing ViewGroup.onInterceptTouchEvent() is just not enough in any occasion because child views can call ViewParent.requestDisallowInterceptTouchEvent() and if the child does that your view will stop receiving calls to interceptTouchEvent (see here for an example on when I child you can do that).

Here's a class I wrote and use when I need something like this, it's custom FrameLayout that gives full control on touch events on any delegator

import android.annotation.TargetApi;
import android.content.Context;
import android.os.Build;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.widget.FrameLayout;

/**
 * A FrameLayout that allow setting a delegate for intercept touch event
 */
public class InterceptTouchFrameLayout extends FrameLayout {
    private boolean mDisallowIntercept;

    public interface OnInterceptTouchEventListener {
        /**
         * If disallowIntercept is true the touch event can't be stealed and the return value is ignored.
         * @see android.view.ViewGroup#onInterceptTouchEvent(android.view.MotionEvent)
         */
        boolean onInterceptTouchEvent(InterceptTouchFrameLayout view, MotionEvent ev, boolean disallowIntercept);

        /**
         * @see android.view.View#onTouchEvent(android.view.MotionEvent)
         */
        boolean onTouchEvent(InterceptTouchFrameLayout view, MotionEvent event);
    }

    private static final class DummyInterceptTouchEventListener implements OnInterceptTouchEventListener {
        @Override
        public boolean onInterceptTouchEvent(InterceptTouchFrameLayout view, MotionEvent ev, boolean disallowIntercept) {
            return false;
        }
        @Override
        public boolean onTouchEvent(InterceptTouchFrameLayout view, MotionEvent event) {
            return false;
        }
    }

    private static final OnInterceptTouchEventListener DUMMY_LISTENER = new DummyInterceptTouchEventListener();

    private OnInterceptTouchEventListener mInterceptTouchEventListener = DUMMY_LISTENER;

    public InterceptTouchFrameLayout(Context context) {
        super(context);
    }

    public InterceptTouchFrameLayout(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public InterceptTouchFrameLayout(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    @TargetApi(Build.VERSION_CODES.LOLLIPOP)
    public InterceptTouchFrameLayout(Context context, AttributeSet attrs, int defStyleAttr, int defStyle) {
        super(context, attrs, defStyleAttr, defStyle);
    }

    @Override
    public void requestDisallowInterceptTouchEvent(boolean disallowIntercept) {
        getParent().requestDisallowInterceptTouchEvent(disallowIntercept);
        mDisallowIntercept = disallowIntercept;
    }

    public void setOnInterceptTouchEventListener(OnInterceptTouchEventListener interceptTouchEventListener) {
        mInterceptTouchEventListener = interceptTouchEventListener != null ? interceptTouchEventListener : DUMMY_LISTENER;
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        boolean stealTouchEvent = mInterceptTouchEventListener.onInterceptTouchEvent(this, ev, mDisallowIntercept);
        return stealTouchEvent && !mDisallowIntercept || super.onInterceptTouchEvent(ev);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        boolean handled = mInterceptTouchEventListener.onTouchEvent(this, event);
        return handled || super.onTouchEvent(event);
    }
}

This class provide a setInterceptTouchEventListener() to set your custom interceptor.

When it is required to disallow intercepting touch event it cheat, it pass this to the parent view but keeps intercepting them. However, it does not let the listener intercept events anymore, so if the listener return true on intercept touch event that will be ignored.

This way you can transparently receive every touch event that pass through your ViewGroup without disrupting the children views behavior.