Alexander Alexander - 6 months ago 90
Objective-C Question

Why does UINavigationBar steal touch events?

I have a custom UIButton with UILabel added as subview. Button perform given selector only when I touch it about 15points lower of top bound. And when I tap above that area nothing happens.

I found out that it hasn't caused by wrong creation of button and label, because after I shift the button lower at about 15 px it works correctly.

UPDATE I forgot to say that button located under the UINavigationBar and 1/3 of upper part of the button don't get touch events.

Image here
]([Image here)

View with 4 buttons is located under the NavigationBar. And when touch the "Basketball" in top, BackButton get touch event, and when touch "Piano" in top, then rightBarButton (if exists) get touch.If not exists, nothing happened.

I didn't find this documented feature in App docs.

Also I found this topic related to my problem,but there is no answer too.

Answer

I found out the answer here(Apple Developer Forum).

Apple Support:

I recommend that you avoid having touch-sensitive UI in such close proximity to the nav bar or toolbar. These areas are typically known as "slop factors" making it easier for users to perform touch events on buttons without the difficulty of performing precision touches. This is also the case for UIButtons for example.

But if you want to capture the touch event before the navigation bar or toolbar receives it, you can subclass UIWindow and override: -(void)sendEvent:(UIEvent *)event;

Also I found out,that when I touch the area under the UINavigationBar, the location.y defined as 64,though it was not. So I made this:

CustomWindow.h

@interface CustomWindow: UIWindow 
@end

CustomWindow.m

@implementation CustomWindow
- (void) sendEvent:(UIEvent *)event
{       
  BOOL flag = YES;
  switch ([event type])
  {
   case UIEventTypeTouches:
        //[self catchUIEventTypeTouches: event]; perform if you need to do something with event         
        for (UITouch *touch in [event allTouches]) {
          if ([touch phase] == UITouchPhaseBegan) {
            for (int i=0; i<[self.subviews count]; i++) {
                //GET THE FINGER LOCATION ON THE SCREEN
                CGPoint location = [touch locationInView:[self.subviews objectAtIndex:i]];

                //REPORT THE TOUCH
                NSLog(@"[%@] touchesBegan (%i,%i)",  [[self.subviews objectAtIndex:i] class],(NSInteger) location.x, (NSInteger) location.y);
                if (((NSInteger)location.y) == 64) {
                    flag = NO;
                }
             }
           }  
        }

        break;      

   default:
        break;
  }
  if(!flag) return; //to do nothing

    /*IMPORTANT*/[super sendEvent:(UIEvent *)event];/*IMPORTANT*/
}

@end

In AppDelegate class I use CustomWindow instead of UIWindow.

Now when I touch area under navigation bar, nothing happens.

My buttons still don't get touch events,because I don't know how to send this event (and change coordinates) to my view with buttons.