Question

How can I add key (an int) and value (an int) pair to a NSDictionary object? and how can they be retrieved as int?

Thanks!

Answer 1

The dictionary key and value has to be a object reference (id) so you can’t use an integer as the key. You should instead wrap your integers in a NSNumber:

[NSNumber numberWithInt:5]

You can then initialize your NSDictionary using one of the initWithObjects initializers. I chose the initWithObjectsAsKeys: initializer which accepts key/values in a value, key, value, key.. nil format.

NSDictionary *dict = [[NSDictionary alloc]initWithObjectsAndKeys:[NSNumber numberWithInt:15], [NSNumber numberWithInt:5], nil];

To access the value, you need to do the same:

NSLog(@"%@", [dict objectForKey:[NSNumber numberWithInt:5]]);

EDIT: According to your comment, it seems you should be using a NSMutableDictionary, not a NSDictionary. The same thing applies to wrapping your integers, but you’ll want to use the setObject:forKey method:

NSMutableDictionary *dict = [[NSMutableDictionary alloc]init];
[dict setObject:[NSNumber numberWithInt:15] forKey:[NSNumber numberWithInt:5]];   

Does that help?