Ios – Capturing touches on a subview outside the frame of its superview using hitTest:withEvent:

iosobjective cuiview-hierarchy

My problem: I have a superview EditView that takes up basically the entire application frame, and a subview MenuView which takes up only the bottom ~20%, and then MenuView contains its own subview ButtonView which actually resides outside of MenuView's bounds (something like this: ButtonView.frame.origin.y = -100).

(note: EditView has other subviews that are not part of MenuView's view hierarchy, but may affect the answer.)

You probably already know the issue: when ButtonView is within the bounds of MenuView (or, more specifically, when my touches are within MenuView's bounds), ButtonView responds to touch events. When my touches are outside of MenuView's bounds (but still within ButtonView's bounds), no touch event is received by ButtonView.

Example:

  • (E) is EditView, the parent of all views
  • (M) is MenuView, a subview of EditView
  • (B) is ButtonView, a subview of MenuView

Diagram: 

+------------------------------+
|E                             |
|                              |
|                              |
|                              |
|                              |
|+-----+                       |
||B    |                       |
|+-----+                       |
|+----------------------------+|
||M                           ||
||                            ||
|+----------------------------+|
+------------------------------+

Because (B) is outside (M)'s frame, a tap in the (B) region will never be sent to (M) – in fact, (M) never analyzes the touch in this case, and the touch is sent to the next object in the hierarchy.

Goal: I gather that overriding hitTest:withEvent: can solve this problem, but I don't understand exactly how. In my case, should hitTest:withEvent: be overridden in EditView (my 'master' superview)? Or should it be overridden in MenuView, the direct superview of the button that is not receiving touches? Or am I thinking about this incorrectly?

If this requires a lengthy explanation, a good online resource would be helpful – except Apple's UIView docs, which have not made it clear to me.

Thanks!

Best Answer

I have modified the accepted answer's code to be more generic - it handles the cases where the view does clip subviews to its bounds, may be hidden, and more importantly : if the subviews are complex view hierarchies, the correct subview will be returned.

- (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event {

    if (self.clipsToBounds) {
        return nil;
    }

    if (self.hidden) {
        return nil;
    }

    if (self.alpha == 0) {
        return nil;
    }

    for (UIView *subview in self.subviews.reverseObjectEnumerator) {
        CGPoint subPoint = [subview convertPoint:point fromView:self];
        UIView *result = [subview hitTest:subPoint withEvent:event];

        if (result) {
            return result;
        }
    }

    return nil;
}

SWIFT 3

override func hitTest(_ point: CGPoint, with event: UIEvent?) -> UIView? {

    if clipsToBounds || isHidden || alpha == 0 {
        return nil
    }

    for subview in subviews.reversed() {
        let subPoint = subview.convert(point, from: self)
        if let result = subview.hitTest(subPoint, with: event) {
            return result
        }
    }

    return nil
}

I hope this helps anyone trying to use this solution for more complex use cases.

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