What really happens when call setCancelsTouchesInView?

ios, iphone, objective-c, uigesturerecognizer

Solution

ACB quoted the `UIGestureRecognizer` reference. To make it a little more concrete, suppose you have a view with a pan gesture recognizer attached, and you have these methods in your view controller:

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    NSLog(@"touchesBegan");
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
    NSLog(@"touchesMoved");
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
    NSLog(@"touchesEnded");
}

- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event {
    NSLog(@"touchesCancelled");
}

- (IBAction)panGestureRecognizerDidUpdate:(UIPanGestureRecognizer *)sender {
    NSLog(@"panGesture");
}

And of course the pan gesture recognizer is configured to send the `panGestureRecognizerDidUpdate:` message.

Now suppose you touch the view, move your finger enough for the pan gesture to be recognized, and then lift your finger. What does the app print?

If the gesture recognizer has `cancelsTouchesInView` set to `YES`, the app will log these messages:

touchesBegan
touchesMoved
touchesCancelled
panGesture
panGesture
(etc.)

You might get more than one `touchesMoved` before the cancel.

So, if you set `cancelsTouchesInView` to `YES` (the default), the system will cancel the touch before it sends the first message from the gesture recognizer, and you won't get any more touch-related messages for that touch.

If the gesture recognizer has `cancelsTouchesInView` set to `NO`, the app will log these messages:

touchesBegan
touchesMoved
panGesture
touchesMoved
panGesture
touchesMoved
panGesture
(etc.)
panGesture
touchesEnded

So, if you set `cancelsTouchesInView` to `NO`, the system will continue sending touch-related messages for the gesture touch, interleaved with the gesture recognizer's messages. The touch will end normally instead of being cancelled (unless the system cancels the touch for some other reason, like the home button being pressed during the touch).

Problem

Wondering what really happens when i call setCancelsTouchesInView. It is not covered in the official document http://developer.apple.com/library/ios/#documentation/uikit/reference/UIGestureRecognizer_Class/Reference/Reference.html Thanks

Original source