Question

I had a super noob question about assigning objects in objective-c. I basically am trying to create an array of thumbnails to use. I have this code from another post.

+ (UIImage *)scale:(UIImage *)image toSize:(CGSize)size
{
    UIGraphicsBeginImageContext(size);
    [image drawInRect:CGRectMake(0, 0, size.width, size.height)];
    UIImage *scaledImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return scaledImage;
}

In my viewDidLoad, I do this:

// Create thumbnail images to be used in UITableView.
    NSMutableArray *imageArray = [[NSMutableArray alloc] initWithCapacity:[_list count]];  // list is an array that has my data
    for (id *test in _list) {
        UIImage *cardImage = [UIImage imageNamed:test.ImageFile];  // line 1
        cardImage = [UIImage scale:cardImage toSize:CGSizeMake(50, 50)];  // line 2
        [imageArray addObject:cardImage];  // line 3
    }
    self.List = imageArray;
    [imageArray release];

My question is in regards to inside the for loop. This is my understanding of how it works, please correct me if I’m wrong.

Line 1 creates an autorelease UIImage called cardImage.

Line 2 creates another UIImage from the scale:toSize: method. (I’m not sure if this UIImage is autoreleased or not). cardImage now points to this new UIImage created in line 2 and the autoreleased UIImage from line 1 will later be cleaned up.

Line 3 adds that new object to imageArray.

I wasn’t sure if this was right/wrong/good/bad, etc. I know with primitive types in a method, you can do

int x = 5;
x = 10;

But I wasn’t sure if I was creating a memory leak here by doing this, and if there was a better method. Thanks a bunch!

Answer 1

+ (UIImage *)scale:(UIImage *)image toSize:(CGSize)size
{
    ...
    UIImage *scaledImage = UIGraphicsGetImageFromCurrentImageContext();
    ...
    return scaledImage;
}

UIGraphicsGetImageFromCurrentImageContext returns an autoreleased image so does scale:toSize:. Therefore, your loop does not leak.

Your first clue could have been the name: scale:toSize:. According to the Memory Management Rules, only methods whose names begin with “alloc”, “new”, “copy” or “mutableCopy” return objects you own. Other methods return objects you do not own.