Observe when UITabBar is Hidden from Delegate

How do I add an observer for when a UITabBar is hidden (through 'hides-bottom-bar-when-pushed')? I have a custom button that sits underneath my tab bar an开发者_StackOverflow社区d I want to make sure it doesn't appear when the UITabBar is hidden. Thanks!

Try using the UINavigationControllerDelegate protocol:

- (void)navigationController:(UINavigationController *)navigationController 
      willShowViewController:(UIViewController *)viewController
                    animated:(BOOL)animated
{
    if (viewController.hidesBottomBarWhenPushed) {
        // ...
    }
}

The best option is to place your UIToolbar inside a UIView that has clipping enabled and position the clip-view just above the UITabBar. Then add this UIView as a subview of your UITabBar. This way showing and hiding the UITabBar will automatically show or hide your UIToolbar Now you can animate the showing and hiding of your UIToolbar and still have it disappear each time the UITabBar does.

This will tell you when the value of that field changes:

 UITabBar *myTabBar = [[UITabBar alloc] init];

 [self addObserver:myInterestedObjectWhoWantsToKnowWhenTabBarHiddenChanges
        forKeyPath:@"myTabBar.hidesBottomBarWhenPushed"
           options:NSKeyValueObservingOptionNew
           context:nil];

Then in myInterestedObjectWhoWantsToKnowWhenTabBarHiddenChanges.m, implement

     - (void)observeValueForKeyPath:(NSString *)keyPath 
                  ofObject:(id)object 
                    change:(NSDictionary *)change
                   context:(void *)context {    

               if ([keyPath isEqualToString:@"myTabBar.hidesBottomBarWhenPushed"]) {  // this key must match, where observer is set.        
                    // object will be "self" from the code above
                    // and the change dictionary will have the old and new values.
               }
       }