How to cancel UIGestureRecognizer if subview's button pressed

Question

I am struggling to get the behaviour I would like from the gesture recognisers, specifically cancelling certain gestures if others have fired.

I have a scrollView set to paging and multiple subviews in each page. I have added a touch gesture recogniser to scroll to the next or prev page if the user taps to the right or left of the page.

    // Add a gesture recogniser turn pages on a single tap at the edge of a page
    UITapGestureRecognizer *tapGesture = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(tapGestureHandler:)];
    tapGesture.cancelsTouchesInView = NO;
    [self addGestureRecognizer:tapGesture];
    [tapGesture release];

and my gesture handler:

- (void) tapGestureHandler:(UIGestureRecognizer *) gestureRecognizer {
    const CGFloat kTapMargin = 180;

    // Get the position of the point tapped in the window co-ordinate system
    CGPoint tapPoint = [gestureRecognizer locationInView:nil];

    // If the tap point is to the left of the page then go back a page
    if (tapPoint.x > (self.frame.size.width - kTapMargin)) [self scrollRectToVisible:pageViewRightFrame animated:YES];

    // If the tap point is to the right of the page then go forward a page
    else if (tapPoint.x < kTapMargin) [self scrollRectToVisible:pageViewLeftFrame animated:YES];
}

All works well, except where I have a subview on the page that has buttons in it. I want to be able to ignore the tap to turn the page if the user touches a button on the subView and I can't figure out how to do this.

Cheers

Dave

Answer 1

The solution that worked the best for me in the end was to use the hitTest to determine if there were any buttons underneath the location of the tap gesture. If there are then just ignore the rest of the gesture code.

Seems to work well. Would like to know if there are any gotchas with what I have done.

- (void) tapGestureHandler:(UIGestureRecognizer *) gestureRecognizer {
    const CGFloat kTapMargin = 180;

    // Get the position of the point tapped in the window co-ordinate system
    CGPoint tapPoint = [gestureRecognizer locationInView:nil];

    // If there are no buttons beneath this tap then move to the next page if near the page edge
    UIView *viewAtBottomOfHeirachy = [self.window hitTest:tapPoint withEvent:nil];
    if (![viewAtBottomOfHeirachy isKindOfClass:[UIButton class]]) {

        // If the tap point is to the left of the page then go back a page
        if (tapPoint.x > (self.bounds.size.width - kTapMargin)) [self scrollRectToVisible:pageViewRightFrame animated:YES];

        // If the tap point is to the right of the page then go forward a page
        else if (tapPoint.x < kTapMargin) [self scrollRectToVisible:pageViewLeftFrame animated:YES];
    }   
}

Answer 2

Apple documentation shows the answer:

- (void)viewDidLoad {
      [super viewDidLoad];
      // Add the delegate to the tap gesture recognizer
      self.tapGestureRecognizer.delegate = self;
}

// Implement the UIGestureRecognizerDelegate method
-(BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldReceiveTouch:    (UITouch *)touch {
      // Determine if the touch is inside the custom subview
     if ([touch view] == self.customSubview){
         // If it is, prevent all of the delegate's gesture recognizers
         // from receiving the touch
        return NO;
     }
     return YES;
}

Of course in this case customSubview would be subview on the page that has buttons in it (or even the buttons on it)

Answer 3

Swift 3

Set UITapGestureRecognizer

let tap = UITapGestureRecognizer(target: self, action: #selector(Class.didTap))
tap.delegate = self

UITapGestureRecognizer delegate method:

func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, shouldReceive touch: UITouch) -> Bool {
    return touch.view != buttonThatShouldCancelTapGesture
}

Answer 4

You can subclass UIView and overwrite the -touchesBegan selector, or you can play with the opaque property of the subviews to make them "invisible" to the touches (if view.opaque = NO, the view ignores touch events).