Is there an example of how to use a TouchDelegate in Android to increase the size of a view's click target?

Question

My understanding is that when you have a view that\'s too small to easily touch, you\'re supposed to use a TouchDelegate to increase the clickable region for that view.

Answer 1

Because I didn't like the idea of waiting for the layout pass just to get the new size of the TouchDelegate's rectangle, I went for a different solution:

public class TouchSizeIncreaser extends FrameLayout {
    public TouchSizeIncreaser(@NonNull Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent event) {
        return true;
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        final View child = getChildAt(0);
        if(child != null) {
            child.onTouchEvent(event);
        }
        return true;
    }
}

And then, in a layout:

<ch.tutti.ui.util.TouchSizeIncreaser
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:padding="10dp">

    <Spinner
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"/>
</ch.tutti.ui.util.TouchSizeIncreaser>

The idea is that TouchSizeIncreaser FrameLayout will wrap the Spinner (could be any child View) and forward all the touch events captured in it's hit rect to the child View. It works for clicks, the spinner opens even if clicked outside its bounds, not sure what are the implications for other more complex cases.

Answer 2

I asked a friend at Google and they were able to help me figure out how to use TouchDelegate. Here's what we came up with:

final View parent = (View) delegate.getParent();
parent.post( new Runnable() {
    // Post in the parent's message queue to make sure the parent
    // lays out its children before we call getHitRect()
    public void run() {
        final Rect r = new Rect();
        delegate.getHitRect(r);
        r.top -= 4;
        r.bottom += 4;
        parent.setTouchDelegate( new TouchDelegate( r , delegate));
    }
});

Answer 3

emmby's approch didn't work for me but after a little changes it did:

private void initApplyButtonOnClick() {
    mApplyButton.setOnClickListener(onApplyClickListener);
    final View parent = (View)mApplyButton.getParent();
    parent.post(new Runnable() {

        @Override
        public void run() {
            final Rect hitRect = new Rect();
            parent.getHitRect(hitRect);
            hitRect.right = hitRect.right - hitRect.left;
            hitRect.bottom = hitRect.bottom - hitRect.top;
            hitRect.top = 0;
            hitRect.left = 0;
            parent.setTouchDelegate(new TouchDelegate(hitRect , mApplyButton));         
        }
    });
}

Maybe it can save someone's time

Answer 4

To expand the touch area generically with pretty few restrictions use the following code.

It lets you expand the touch area of the given view within the given ancestor view by the given expansion in pixels. You can choose any ancestor as long as the given view is in the ancestors layout tree.

    public static void expandTouchArea(final View view, final ViewGroup ancestor, final int expansion) {
    ancestor.post(new Runnable() {
        public void run() {
            Rect bounds = getRelativeBounds(view, ancestor);
            Rect expandedBounds = expand(bounds, expansion);
            // LOG.debug("Expanding touch area of {} within {} from {} by {}px to {}", view, ancestor, bounds, expansion, expandedBounds);
            ancestor.setTouchDelegate(new TouchDelegate(expandedBounds, view));
        }

        private Rect getRelativeBounds(View view, ViewGroup ancestor) {
            Point relativeLocation = getRelativeLocation(view, ancestor);
            return new Rect(relativeLocation.x, relativeLocation.y,
                            relativeLocation.x + view.getWidth(),
                            relativeLocation.y + view.getHeight());
        }

        private Point getRelativeLocation(View view, ViewGroup ancestor) {
            Point absoluteAncestorLocation = getAbsoluteLocation(ancestor);
            Point absoluteViewLocation = getAbsoluteLocation(view);
            return new Point(absoluteViewLocation.x - absoluteAncestorLocation.x,
                             absoluteViewLocation.y - absoluteAncestorLocation.y);
        }

        private Point getAbsoluteLocation(View view) {
            int[] absoluteLocation = new int[2];
            view.getLocationOnScreen(absoluteLocation);
            return new Point(absoluteLocation[0], absoluteLocation[1]);
        }

        private Rect expand(Rect rect, int by) {
            Rect expandedRect = new Rect(rect);
            expandedRect.left -= by;
            expandedRect.top -= by;
            expandedRect.right += by;
            expandedRect.bottom += by;
            return expandedRect;
        }
    });
}

Restrictions that apply:

• The touch area can not exceed the bounds of the view's ancestor since the ancestor must be able to catch the touch event in order to forward it to the view.
• Only one TouchDelegate can be set to a ViewGroup. If you want to work with multiple touch delegates, choose different ancestors or use a composing touch delegate like explained in How To Use Multiple TouchDelegate.

Answer 5

I was able to accomplish this with multiple views (checkboxes) on one screen drawing largely from this blog post. Basically you take emmby's solution and apply it to each button and its parent individually.

public static void expandTouchArea(final View bigView, final View smallView, final int extraPadding) {
    bigView.post(new Runnable() {
        @Override
        public void run() {
            Rect rect = new Rect();
            smallView.getHitRect(rect);
            rect.top -= extraPadding;
            rect.left -= extraPadding;
            rect.right += extraPadding;
            rect.bottom += extraPadding;
            bigView.setTouchDelegate(new TouchDelegate(rect, smallView));
        }
   });
}

In my case I had a gridview of imageviews with checkboxes overlaid on top, and called the method as follows:

CheckBox mCheckBox = (CheckBox) convertView.findViewById(R.id.checkBox1);
final ImageView imageView = (ImageView) convertView.findViewById(R.id.imageView1);

// Increase checkbox clickable area
expandTouchArea(imageView, mCheckBox, 100);

Working great for me.

Answer 6

Isn't it the better Idea of giving Padding to that particular component(Button).