Sibling subview does not receive touches in iPhone

Question

I have a view (parent) with two subviews, one on top (topChild) of the other (bottomChild).

If I tap on the screen only topChild and parent receive the touch event.

What should I change to propagate the touch event to bottomChild as well?

The code:

- (void)viewDidLoad
{
    [super viewDidLoad];
    MYView* parent = [[MYView alloc] initWithFrame:CGRectMake(0, 0, 100, 100)];
    parent.tag = 3;
    parent.backgroundColor = [UIColor redColor];

    MYView* bottomChild = [[MYView alloc] initWithFrame:CGRectMake(0, 0, 90, 90)];
    bottomChild.tag = 2;
    bottomChild.backgroundColor = [UIColor blueColor];
    [parent addSubview:bottomChild];

    MYView* topChild = [[MYView alloc] initWithFrame:CGRectMake(0, 0, 80, 80)];
    topChild.tag = 1;
    topChild.backgroundColor = [UIColor greenColor];
    [parent addSubview:topChild];
    [self.view addSubview:parent];
}

Where MYView is a subclass of UIView that only logs touchesBegan.

- (void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    NSLog(@"%d", self.tag);
    [super touchesBegan:touches withEvent:event];
}

The result:

enter image description here

Touching the green area produces the following log:

TouchTest[25062:f803] 1
TouchTest[25062:f803] 3

My first idea was to make parent propagate all the touchesSomething calls to its children but (A) I suspect there might be an easier solution and (B) I don't know which child sent the event to parent, and sending touchesSomething messages twice to the same view might cause shenanigans.

After asking the question I've found this post that suggests to override hitTest to change the view that receives the touches. I will try this approach and update the question if it works.

Adam Eberbach · Accepted Answer · 2011-12-18T22:11:51.420

1

It's an interesting problem you have that is probably something best addressed through a rethink of the way you have things structured. But to make it work the way you suggest you need to catch the touch event in the current top view, pass it to the parent and then propagate it down through all subviews of the parent view. To make this work you would need the touchesBegan: (or whatever other method you use to intercept the touch) to do nothing in all the views, doing the action only in the method called by the parent view.

Which is really another way of saying don't handle touches in the views, catch them but notify the parent view view and then call subview methods as required to cause the effect you want.

- (void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {

    // Do nothing, parent view calls my parentNotifiedTouchesBegan method
    [self.superview touchesBegan:touches withEvent:event];
}

- (void) parentNotifiedTouchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {

    // Act on the touch here just as my sibling views are doing
}

Note I changed super to self.superview in that code. You may or may not also want to call super's method depending on what you are doing, and the place to call that may be in parentNotifiedTouchesBegan.

You can know which subView sent the event of course, just use a custom method to notify the superview instead of calling its touchesBegan:. Use a self argument.

edited Dec 18 '11 at 22:11

answered Dec 18 '11 at 22:06

Adam Eberbach

12,309
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Thanks Adam! Would this solution be compatible with gesture recognizers? At first glance it looks like I will have to reimplement the wheel if I go this route. – hpique Dec 18 '11 at 22:13
And I would very much like to re-structure things, but I don't see how in my case. topChild has transparency, both topChild and bottomChild can "move" (thus topChild cannot be a subview of bottomChild), and both need to respond to touches. – hpique Dec 18 '11 at 22:14
It should be possible, you would just be passing the gestureRecognizer object received by the callback up to the parent rather than a simple touch. At least in the project I have handy this would work for UIPinchGestureRecognizer. – Adam Eberbach Dec 18 '11 at 22:17
Now I'm thinking you don't need to catch events in subviews at all, in fact you can disable interaction so that the base view gets everything. No need to do the notification step. Just have base view catch and interpret everything and cause the views to act. You should be able to isolate the views that should get the event by comparing the point (- (CGPoint)convertPoint:(CGPoint)point toView:(UIView *)view) to the subview's frames (CGRectContainsPoint). – Adam Eberbach Dec 18 '11 at 22:22
That was what I was trying now! That said, I find it very strange that this has to be done "manually". I would imagine this is a pretty common problem. – hpique Dec 18 '11 at 22:24

score 0 · Answer 2 · answered Dec 20 '11 at 17:33

0

If you don't need the touches on the children then set

bottomChild.userInteractionEnabled = NO;
topChild.userInteractionEnabled = NO;

answered Dec 20 '11 at 17:33

ader

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Sibling subview does not receive touches in iPhone

2 Answers2