NSArray containsObject method
The documentation for [NSArray containsObject:] says:
This method determines whether anObject is present in the receiver by sending an isEqual: message to each of the receiver’s objects (and passing anObject as the parameter to each isEqual: message).
The problem is that you are comparing references to objects rather than the values of the objects. To make this specific example work, you will either need to send [collection containsObject:] an instance of a variable it contains (e.g. A, B, or C), or you will need to override the [NSObject isEqual:] method in your Item class.
This is what your isEqual method might look like:
- (BOOL)isEqual:(id)other { if (other == self) return YES; if (!other || ![other isKindOfClass:[self class]]) return NO; if (self.length != other.length || self.width != other.width || self.height != other.height) return NO; return YES;}For a better implementation, you may want to look at this question.