KVO 检查目标 c 中 UIView 中所有子视图的 clipsToBounds 的变化

Question

I am trying to implement a KVO example for clipsToBounds property of all subviews in my UIView. I do not quite understand how to change the value in observeValueForKeyPath method. I am using this code:

-(void)ViewDidLoad{
        [self.navigationController.view addObserver:self forKeyPath:@"clipsToBounds" options:NSKeyValueObservingOptionNew |
         NSKeyValueObservingOptionOld context:nil];
    }
    
    -(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
    NSLog(@"Triggered...")
    }

It is triggered when ever i change the property clipToBounds of a subview that exists in the UIView i have. I need to change the value back to false for every trigger that happens. What should i write inside the observeValueForKeyPath to change the clipsToBounds property? Any help appreciated.

Answer 1

of course adding the Observer must be done before it works. Guessing your typo in "ViewDidLoad" would just never be called because it should be "viewDidLoad". Apart from that your KVO pattern could look like..

static void *kvoHelperClipsToBounds = &kvoHelperClipsToBounds;

-(void)viewDidLoad {
    [self.navigationController.view addObserver:self forKeyPath:@"clipsToBounds" options:NSKeyValueObservingOptionNew context:kvoHelperClipsToBounds];
}
    
-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
    if (context == kvoHelperClipsToBounds) {
        NSLog(@"context compare Triggered...");
    } 

    // or compare against the keyPath
    else if ([keyPath isEqualToString:@"clipsToBounds"]) {
        NSLog(@"classic Key compare Triggered...");
    }
    else
    [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
}

Sidenote: the context just needs to be unique to distinguish it from other KVO.. it could also be reference to a real objects pointer.

Don't forget added Observers must be removed before deallocation.