NSObject+RegisterObserverAdditions.h

#import <Foundation/Foundation.h>

@interface NSObject (RegisterObserverAdditions)


-(void) registerObserver:(NSObject *)observer 
			  forKeyPath:(NSString *)keyPath
				 options:(NSKeyValueObservingOptions)options 
				 context:(void *)context;

-(void) unregisterAllObservers;

@end

NSObject+RegisterObserverAdditions.m

#import "NSObject+RegisterObserverAdditions.h"
#import <objc/runtime.h>

#define kObservedKeyPaths		@"__observedKeyPaths"

@interface NSObject()
-(NSMutableArray *) observedKeyPaths;
@end

@implementation NSObject (RegisterObserverAdditions)


-(void) registerObserver:(NSObject *)observer 
			  forKeyPath:(NSString *)keyPath
				 options:(NSKeyValueObservingOptions)options 
				 context:(void *)context
{
	if( [[self observedKeyPaths] containsObject: keyPath] )
		return;
	
	[self addObserver: observer forKeyPath: keyPath options: options context: context];
	[[self observedKeyPaths] addObject: keyPath];
}

-(void) unregisterAllObservers
{
	for( NSString *keyPath in [self observedKeyPaths] )
	{
		[self removeObserver: self forKeyPath: keyPath];
	}
	[[self observedKeyPaths] removeAllObjects];
}


#pragma mark- Internal Methods

-(NSMutableArray *) observedKeyPaths
{
	NSMutableArray *observered = objc_getAssociatedObject( self, kObservedKeyPaths);
	if( !observered )
	{
		observered = [NSMutableArray array];
		objc_setAssociatedObject(  self, kObservedKeyPaths, observered, OBJC_ASSOCIATION_RETAIN);
	}
	return observered;
}

@end

NSObjectRegisterObserverAdditions.h

#import <Foundation/Foundation.h>

@interface NSObject (RegisterObserverAdditions)


-(void) registerObserver:(NSObject *)observer 
			  forKeyPath:(NSString *)keyPath
				 options:(NSKeyValueObservingOptions)options 
				 context:(void *)context;

-(void) unregisterAllObservers;

@end

NSObjectRegisterObserverAdditions.m

#import "NSObject+RegisterObserverAdditions.h"
#import <objc/runtime.h>

#define kObservedKeyPaths		@"__observedKeyPaths"

@interface NSObject()
-(NSMutableArray *) observedKeyPaths;
@end

@implementation NSObject (RegisterObserverAdditions)


-(void) registerObserver:(NSObject *)observer 
			  forKeyPath:(NSString *)keyPath
				 options:(NSKeyValueObservingOptions)options 
				 context:(void *)context
{
	if( [[self observedKeyPaths] containsObject: keyPath] )
		return;

	[self addObserver: observer forKeyPath: keyPath options: options context: context];
	[[self observedKeyPaths] addObject: keyPath];
}

-(void) unregisterAllObservers
{
	for( NSString *keyPath in [self observedKeyPaths] )
	{
		[self removeObserver: self forKeyPath: keyPath];
	}
	[[self observedKeyPaths] removeAllObjects];
}


#pragma mark- Internal Methods

-(NSMutableArray *) observedKeyPaths
{
	NSMutableArray *observed = objc_getAssociatedObject( self, kObservedKeyPaths);
	if( !observed )
	{
		observed = [NSMutableArray array];
		objc_setAssociatedObject(  self, kObservedKeyPaths, observed, OBJC_ASSOCIATION_RETAIN);
	}
	return observed;
}

@end