Question

I am currently trying to write a class to create faux grid system to keep track of a NSMutableArray of game entities using a NSMutableArray of NSMutableArrays. Given my limited experience with Objective-C programming, I am unsure of how certain things work.

Here is the init method:

#define MAX_BALL_ROWCOUNT 6
#define MAX_BALL_COLCOUNT 4
- (id) initWithMutableArray:(NSMutableArray *)aList {
self = [super init];
if (self != nil) {
    ballList = [[NSMutableArray alloc] initWithCapacity: MAX_BALL_ROWCOUNT];

    for (int i=0; i<MAX_BALL_ROWCOUNT; i++) {
        NSMutableArray *balls = [[NSMutableArray alloc] initWithCapacity:MAX_BALL_COLCOUNT];
        [ballList addObject:balls];
        [balls release];
    }

    int x = 0;

    for (NSMutableArray *array in ballList) {
        for (int i = 0; i<MAX_BALL_COLCOUNT; i++) {
            [array addObject:[aList objectAtIndex:x]];
            x++;
            }
        }
    }

return self;
}

ballList is the class’s NSMutableArray that will store NSMutableArrays.

aList is the NSMutableArray containing the GameEntities I wish to keep track of that is passed into this class.

All the sizes and amount of entities to store are fixed, which is why there is no checks on the sizes of the arrays nor the number of entities to store.

So the first question I have involves freeing memory. This is the dealloc function I currently have:

- (void) dealloc {
    [ballList release];
    [super dealloc];
}

Does calling a release on ballList cause the release to be called on the NSMutableArrays that it contains (which will subsequently call the release on the objects those NSMutableArrays contain) or do I have to write something like:

for (NSMutableArray *array in ballList) {
    [array release];
}
[ballList release];

My second question involves the usage of this array of arrays. Is this the proper way to traverse through ballList?

- (void) update {
    for (NSMutableArray *array in ballList) {
        for (GameEntity *balls in array) {
            (CGPoint) location = [balls getLocation];
            [balls setLocation: CGPointMake(location.x+1, location.y+1)];
        }
    }
}

Lastly, in the code above where it sets the balls location, does it only affect the contents within ballList or does the original aList that is passed into ballList change as well? If the contents in the original aList do not change, how would I write it so that they do?

If people have suggestions for a better way to keep track of the entities in a grid system, I’d be open to those too. Thanks in advance.

Answer 1

1. When the dealloc of a NSArray or NSMutableArray is called, all its contents gets a release message. So when you release ballList, if there there is no other owner (I guess in this case there is none) then its dealloc is called and you don’t need to release the other arrays here.

2. Your loop traversal is fine. Though for 2D arrays instead of NSArray of NSArray I personally prefer pure C 2D array, at least in most of the cases.

3. When you are adding object in this way you are adding a reference in the array. So any change via the array’s reference will be reflected in all references of the object. If you don’t want that then add a copy of the object in the array.