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copied!<p>You can do this very easily by just implementing the observer to compare. Following is just an example to implement the custom observer to compare</p> <pre><code>@implementation NSArray (KVO) - (void)addObserver:(NSObject *)observer toObjectsAtIndexes:(NSIndexSet *)indexes forKeyPath:(NSString *)keyPath options:(NSKeyValueObservingOptions)options context:(void *)context { NSUInteger idx=[indexes firstIndex]; while(idx!=NSNotFound) { [[self objectAtIndex:idx] addObserver:observer forKeyPath:keyPath options:options context:context]; idx=[indexes indexGreaterThanIndex:idx]; } } - (void)removeObserver:(NSObject *)observer fromObjectsAtIndexes:(NSIndexSet *)indexes forKeyPath:(NSString *)keyPath { NSUInteger idx=[indexes firstIndex]; while(idx!=NSNotFound) { [[self objectAtIndex:idx] removeObserver:observer forKeyPath:keyPath]; idx=[indexes indexGreaterThanIndex:idx]; } } -(void)addObserver:(id)observer forKeyPath:(NSString*)keyPath options:(NSKeyValueObservingOptions)options context:(void*)context; { if([isa instanceMethodForSelector:_cmd]==[NSArray instanceMethodForSelector:_cmd]) NSRaiseException(NSInvalidArgumentException,self,_cmd,@"not supported for key path %@ (observer was %@)", keyPath, observer); else [super addObserver:observer forKeyPath:keyPath options:options context:context]; } -(void)removeObserver:(id)observer forKeyPath:(NSString*)keyPath; { if([isa instanceMethodForSelector:_cmd]==[NSArray instanceMethodForSelector:_cmd]) NSRaiseException(NSInvalidArgumentException,self,_cmd,@"not supported for key path %@ (observer was %@)", keyPath, observer); else [super removeObserver:observer forKeyPath:keyPath]; } @end </code></pre>

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