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copied!<p>I was running into the same exception. The root cause for my problem was I was referencing an key/value pair incorrectly. At runtime, the exception "-[__NSCFConstantString objectAtIndex:]: unrecognized selector sent to instance" was being thrown. This perplexed me for longer than I'd care to admit. But I found the solution to my problem, and hope it can help someone else. The code that was throwing the exception follows along with the corrected code.</p> <p>The erroneous code:</p> <pre><code>- (void)testMyUnitTest { WorldObject *worldObject; NSMutableDictionary *worldCoordinatesAll = [[NSMutableDictionary alloc] init]; WorldCoordinate *localWCoordinate = [[WorldCoordinate alloc] init]; // Populate with a world coordinate object [worldCoordinatesAll setObject:[localWCoordinate updateWithLatitude:X2LOC Longitude:Y2LOC Altitude:0] forKey:@"OBJECT 2"]; for (id objectID in worldCoordinatesAll) { localWCoordinate = (WorldCoordinate *)objectID; localWCoordinate.latitude = LATITUDE_1; // Exception being thrown on this line } } </code></pre> <p>The corrected code:</p> <pre><code>- (void)testMyUnitTest { WorldObject *worldObject; NSMutableDictionary *worldCoordinatesAll = [[NSMutableDictionary alloc] init]; WorldCoordinate *localWCoordinate = [[WorldCoordinate alloc] init]; // Populate with a world coordinate object [worldCoordinatesAll setObject:[localWCoordinate updateWithLatitude:X2LOC Longitude:Y2LOC Altitude:0] forKey:@"OBJECT 2"]; for (id key in worldCoordinatesAll) { id value = [worldCoordinatesAll objectForKey:key]; localWCoordinate = (WorldCoordinate *)value; localWCoordinate.latitude = LATITUDE_1; } } </code></pre> <p>I realize that for some, this might seem like a totally obvious mistake. But for some reason, it took me a week to see it. So I hope it helps someone else save themsleves some time. :-)</p>

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