NSDictionary With Integer Values

Question

I'm working on a game with monsters. Each one has a list of stats that are all going to be ints. I can set up each stat as it's own variable but I'd prefer to keep them in an NSDictionary since they are all related. I'm running into a problem when I'm trying to change the value's of each stat.

What I Have:

-(id) init {
    self = [super init];
    if(self) {
        stats = [NSDictionary dictionaryWithObjectsAndKeys:
              @"Attack",  0,
              @"Defense", 0,
              @"Special Attack", 0,
              @"Special Defense", 0,
              @"HP", 0, nil];
    }
    return self;
}

What I want to do

-(void) levelUp {
    self.level++;
    [self.stats objectForKey:@"Attack"] += (level * 5);
    [self.stats objectForKey:@"Defense"] += (level * 5);
    [self.stats objectForKey:@"Special Attack"] += (level * 5);
    [self.stats objectForKey:@"Special Defense"] += (level * 5);
    [self.stats objectForKey:@"HP"] += (level * 5);
}

Error I'm Getting

Arithmetic on pointer to interface 'id', which is not a constant size in non-fragile ABI

So it seems obvious to me that the reason I'm getting the problem is that I'm getting an object returned from objectForKey instead of an integer. So I tried to do the intValue method on the object I'm getting but that gave me another error, specifically:

Assigning to 'readonly' return result of an objective-c message not allowed

I'm out of ideas for how to fix this. Any help? Would it be better to just give up the idea to store them all together and just use an int property for each stat?

Answer 1

1. You can only store objects, not primitives, within Cocoa collection classes, so to store numbers you need to use NSNumber objects.
2. You need to use an NSMutableDictionary if you wish to change the contents later.
3. Your call to dictionaryWithObjectsAndKeys has the keys and values reversed.
4. Your stats object is not being retained, so it will be released next time round the run loop (if you're using manual reference counting, that is).

You want:

stats = [[NSMutableDictionary dictionaryWithObjectsAndKeys:
    [NSNumber numberWithInt:0], @"Attack",
    [NSNumber numberWithInt:0], @"Defense",
    [NSNumber numberWithInt:0], @"Special Attack",
    [NSNumber numberWithInt:0], @"Special Defense",
    [NSNumber numberWithInt:0], @"HP",
    nil] retain];

In order to change the values you need to create a new NSNumber object as they are immutable, so something like:

NSNumber *num = [stats objectForKey:@"Attack"];
NSNumber *newNum = [NSNumber numberWithInt:[num intValue] + (level * 5)];
[stats setObject:newNum forKey:@"Attack"];

All pretty tedious if you ask me; there must be an easier way, for example how about creating an Objective-C class to store and manipulate this stuff?

Answer 2

NSDictionarys store NSObject*s. In order to use them with integer values, you unfortunately need to use something like NSNumber. So your initialization would look like:

-(id) init {
    self = [super init];
    if(self) {
        stats = [NSDictionary dictionaryWithObjectsAndKeys:
              @"Attack",  [NSNumber numberWithInt:0],
              @"Defense", [NSNumber numberWithInt:0],
              @"Special Attack", [NSNumber numberWithInt:0],
              @"Special Defense", [NSNumber numberWithInt:0],
              @"HP", [NSNumber numberWithInt:0], nil];
    }
    return self;
}

Then you would have to retrieve them as numbers:

NSNumber *atk = [self.stats objectForKey:@"Attack"];
int iAtk = [atk intValue];
[self.stats setObject:[NSNumber numberWithInt:iAtk] forKey:@"Attack"];

EDIT

Of course, in order to do this, self.stats needs to be an NSMutableDictionary

Answer 3

Adapting @trojanfoe's answer for modern Objective-C with nice syntax sugar:

stats = [@{@"Attack"          : @0,
           @"Defense"         : @0,
           @"Special Attack"  : @0,
           @"Special Defense" : @0,
           @"HP"              : @0} mutableCopy];

And to update a value:

stats[@"Attack"] = @([stats[@"Attack"] intValue] + (level * 5));