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.
However when I try to add objects to my dictionary I get
[NSMutableDictionary setObject:forKey:]: method only defined for abstract class
NilDictionary.h
@interface NilDictionary : NSMutableDictionary {
}
@end
NilDctionary.m
@implementation NilDictionary
- (id)valueForUndefinedKey:(NSString *)key {
return nil;
}
@end
Do I really have to implement all the methods from NSMutableDictionary again in my subclass or is there some other class I should be subclassing?
Clarification: My original problem came down to me not being able to read the documentation properly.
If you need to subclass NSMutableDictionary check out the correct answer. If you want a dictionary that returns nil when your key is not present, NSMutableDictionary does that already.
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.