rentzsch / JRKVOBlocks

Description

JRKVOBlocks replaces this:

- (void)someMethod:(id)someObject {
	self.someProperty = someObject;
	
	[someObject addObserver:self
				 forKeyPath:@"someKey"
					options:0
					context:NULL];
}

- (void)observeValueForKeyPath:(NSString*)keyPath
					  ofObject:(id)object
						change:(NSDictionary*)change
					   context:(void*)context
{
	// Do something.
}

- (void)dealloc {
	[self removeObserver:_someProperty forKeyPath:@"someKey"];
	[_someProperty release];
	[super dealloc];
}

…with this:

- (void)someMethod:(id)someObject {
	[self jr_observe:someObject keyPath:@"someKey" block:^(JRKVOChange *change){
		// Do something.
	}];
}

Besides redirecting -observeValueForKeyPath:ofObject:change:context: into a simple block callback, it also uses Obj-C associated objects to keep track of the objects you're currently observing and automatically stops observing those when released.

And additional bonus is JRKVOObserver, JRKVOBlocks' internal observer class, offers an enhanced -description method that reports the observer's thread and call-stack of the location of registration.

This code requires 10.6 or later and uses MRC, so you'll need to enable -fno-objc-arc if you want to use it in an ARC project.

Let me know if it works on iOS. I think it should…

JRCallBlockOnObserverThread

JRKVOBlocks also defines a new NSKeyValueObservingOptions flag: JRCallBlockOnObserverThread. The "problem" is that KVO observers are invoked synchronously on the thread that made the change. That's a pain if you want to observe a worker thread and update your UI based on its progress.

By using the JRCallBlockOnObserverThread option your block will be called asynchronously on whatever thread you're on when you register your observation (usually the main thread).