key-value-observing

I feel that i don't fully understand difference between KVO and NSNotification... They seem to be so similar... Could you make some example showing when is best to use one method and when the other ? I don't speak about Bind and IB, but i mean add Observer programmatically in my code with NSNotificationCenter or KVO [self.preferenceController addObserver:self forKeyPath:@"color" options:NSKeyValueObservingOptionOld context:@"Color-change" ]; KVO only works on values, NSNotification can be used for value changes but it can be used for anything and can carry a much greater payload. For example,

What's the use of context parameter in following method which is used to register for key value notifications. The documentations just denotes it as arbitrary set of data. addObserver:self forKeyPath:@"selectedIndex" options:NSKeyValueObservingOptionNew context:nil Can somebody shed some light what's the purpose behind it ... I hope this explanation isn't too abstract to understand. Suppose you create a class MyViewController , which is a subclass of UIViewController . You don't have the source code of UIViewController . Now you decide to make MyViewController use KVO to observe changes to the

When observing a value on an object using addObserver:forKeyPath:options:context: , eventually you'll want to call removeObserver:forKeyPath: on that object to clean up later. Before doing that though, is it possible to check if an object actually is observing that property? I've tried to ensure in my code that an object is only having an observer removed when it needs to be, but there are some cases where it's possible that the observer may try to remove itself twice. I'm working to prevent this, but just in case, I've just been trying to figure out if there's a way to check first if my code

Important: Not all classes are KVO-compliant for all properties. You can ensure your own classes are KVO-compliant by following the steps described in “KVO Compliance.” Typically properties in Apple-supplied frameworks are only KVO-compliant if they are documented as such. This statement leaves me confused. Can't we use KVO for UIKit objects at all? I don't remember seeing any property being documented as KVO compliant. Despite saying otherwise, I am able to use KVO with many properties. Does this mean that I can't rely on it? Any insight into this would be appreciated. JustSid UIKit is mostly

I have an object in objective-c at runtime, from which I only know the KVC key and I need to detect the return value type (e.g. I need to know if its an NSArray or NSMutableArray) of this property, how can I do that? e.James You're talking about runtime property introspection, which happens to be something that Objective-C is very good at . In the case you describe, I'm assuming you have a class like this: @interface MyClass { NSArray * stuff; } @property (retain) NSArray * stuff; @end Which gets encoded in XML something like this: <class> <name>MyClass</name> <key>stuff</key> </class> From

In Objective-C, I would normally use something like this: static NSString *kViewTransformChanged = @"view transform changed"; // or static const void *kViewTransformChanged = &kViewTransformChanged; [clearContentView addObserver:self forKeyPath:@"transform" options:NSKeyValueObservingOptionNew context:&kViewTransformChanged]; I have two overloaded methods to choose from to add an observer for KVO with the only difference being the context argument: clearContentView.addObserver(observer: NSObject?, forKeyPath: String?, options: NSKeyValueObservingOptions, context: CMutableVoidPointer)