Copying the contents of an NSMutableDictionary into another NSMutableDictionary?

Question

I have an NSMutableDictionary each element of which is another dictionary. What is the best way I can copy its contents into another NSMutableDictionary? I've tried using:

firstDictionary = [NSMutableDictionary dictionaryWithDictionary:secondDictionary];

However not sure if this is the best way to do it.

Answer 1

Check the NSDictionary initWithDictionary:copyItems: method.

It it enables deep copying of elements thru calling copyWithZone: method of item's class. You will have to take care of copying the fields yourself within the method.

Answer 2

You can also jump between mutable and non-mutable dictionaries using copy and mutableCopy.

- (void) someFunc:(NSMutableDictionary *)myDict {
    NSDictionary *anotherDict = [myDict copy];
    NSMutableDictionary *yetAnotherDict = [anotherDict mutableCopy];
}

Answer 3

What do you mean by "best"?
Anyway, I listed some ways here:

1. firstDictionary = [NSMutableDictionary dictionaryWithDictionary:secondDictionary];
2. [[NSDictionary alloc] initWithDictionary:secondDictionary]; //don't forget to release later
3. using deep copy
4. using shallow copy

Answer 4

Conform to NSCopying Protocol and do copyWithZone on every object.

If NsMutableDictionary contains another dictionary, which contains another dictionary,, then you need to do copyWithZone on each dictionary at all levels.