Expanding the touch area of a ViewPager

Question

My App uses the following ViewPager:

The ViewPager has the same width as the display.

I added margins to the ViewPager in xml so that I can see the left(blue) and right(gray) page. As a result everything works fine but I can only touch onto the green area to move the pages.

I want to expand the touch area to the whole screen so that I am able to touch anywhere to move the ViewPager.

I tried to add a TouchDelegate:

binding.pagerContainer.post {
        val rect = Rect()  
        binding.touchArea.getHitRect(rect)
        binding.pagerContainer.touchDelegate = TouchDelegate(rect, binding.viewPager)
    }

And in the xml:

 <FrameLayout
        android:id="@+id/pager_container"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_centerVertical="true"
        android:clipChildren="false">

        <android.support.v4.view.ViewPager
            android:id="@+id/viewPager"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_gravity="center"
            android:layout_marginBottom="150dp"
            android:layout_marginLeft="70dp"
            android:layout_marginRight="70dp"
            android:layout_marginTop="150dp"
            android:clipChildren="false"/>

        <View
            android:id="@+id/touchArea"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:alpha="0">
        </View>
    </FrameLayout>

The Rect has the correct size. I am posting a Runnable to be sure that the views are laid out. I read the documentation of the TouchDelegate.

I have no idea why it's not working.

Answer 1

OK. I think I have it this time. After some research here and here, I've come up with this answer. Instead of trying to expand the area of ViewPager with TouchDelegate, I've re-routed touch events from the FrameLayout to the ViewPager. 1st, make your own FrameLayout

public class MyFrameLayout extends FrameLayout {

    // make sure to include all the necessary constructors here
    // with calls to super

    // only need to override 1 method
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        ViewPager pager = null;
        int count = getChildCount();
        for(int i=0; i<count; i++) {
            if(getChildAt(i) instanceof ViewPager) {
                pager = (ViewPager)getChildAt(i);
                break;
            }
        }
        if(pager != null) {
            return pager.onTouchEvent(event);
        }
        return super.onTouchEvent(event);
    }
}

If you know that the ViewPager will always be in the same place in the FrameLayout, the onTouchEvent() can be simplified to

    ViewPager pager = (ViewPager)getChildAt(0); 
    return pager.onTouchEvent(event);

Then you use your custom FrameLayout in the layout file

 <your.package.name.MyFrameLayout
    android:id="@+id/pager_container"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    etc. etc.

I've tested it and this does it for me. Hope it works for you.