StackOverflow2013

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copied!<p>Here is the problem:</p> <p>[self willChangeValueForKey:keyPath]; <--- At this point in time the actual observer needs to unsubscribe to street [self didChangeValueForKey:keyPath]; <--- and add itself to the new value. </p> <p>By not providing the new value you are denying the observer the opportunity to unsubscribe.</p> <p>Here is a hacked version that works and demonstrates the problem.</p> <pre><code>/* --- Bridge ----------------------------------------- */ .... ..... @interface Bridge : NSObject { NSMutableDictionary* observedKeys; NSObject* obj; //**** Dictionary for old values just before we send the didChangeValue notification. NSMutableDictionary * oldValues; } ... ..... - (id)init { if( !( self = [super init] ) ) { return nil; } observedKeys = [NSMutableDictionary new]; //************* Initialize the new dictionary oldValues = [NSMutableDictionary new]; return self; } .... ..... - (void) observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context { NSLog( @">>>> Detected Change in keyPath: %@", keyPath ); // **** Cache the old value before telling everyone its going to change. [oldValues setValue:[change valueForKey:NSKeyValueChangeOldKey] forKey:keyPath]; [self willChangeValueForKey:keyPath]; // **** Simulate the change by removing the old value. [oldValues removeObjectForKey:keyPath]; // **** Now when we say we did change the value, we are not lying. [self didChangeValueForKey:keyPath]; } -(id)valueForUndefinedKey:(NSString*)key { // **** Important part, return oldvalue if it exists id oldValue; if(oldValue = [oldValues valueForKey:key]){ return oldValue; } /* Register an observer for the key, if not already done */ if( ![observedKeys objectForKey:key] ) { [observedKeys setObject:[NSNumber numberWithBool:YES] forKey:key]; NSLog(@"adding observer for:%@", key); [obj addObserver:self forKeyPath:key options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld context:nil]; } return [obj valueForKey:key]; } .... ...... </code></pre>

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