Subclassing NSMutableDictionary

Question

I am trying to implement a subclass of NSMutableDictionary that returns nil instead of throwing a NSUndefinedKeyException when the key is not present in the Dictionary.

Answer 1

NSMutableDictionary Class Reference says:

In a subclass, you must override both of its primitive methods:

1. setObject:forKey:
2. removeObjectForKey:

You must also override the primitive methods of the NSDictionary class.

---

NSDictionary Class Reference says:

If you do need to subclass NSDictionary, you need to take into account that is represented by a Class cluster—there are therefore several primitive methods upon which the methods are conceptually based:

1. count
2. objectForKey:
3. keyEnumerator
4. initWithObjects:forKeys:count:

In a subclass, you must override all these methods.

NSDictionary’s other methods operate by invoking one or more of these primitives. The non-primitive methods provide convenient ways of accessing multiple entries at once.

---

It seems that you need to override all these six methods to make your NSMutableDictionary subclass work perfect.