Memory Leak with ARC

问题:

+(void)setup {
    UIImage* spriteSheet = [UIImage imageNamed:@"mySpriteSheet.png"];
    CGRect rect;
    animation = [NSMutableArray arrayWithCapacity:numberOfFramesInSpriteSheet];
    int frameCount = 0;

    for (int row = 0; row < numberFrameRowsInSpriteSheet; row++) {
        for (int col = 0; col < numberFrameColsInSpriteSheet; col++) {
            frameCount++;
            if (frameCount <= numberOfFramesInSpriteSheet) {
                rect = CGRectMake(col*frameHeight, row*frameWidth, frameHeight, frameWidth);
                [animation addObject:[UIImage imageWithCGImage:CGImageCreateWithImageInRect(spriteSheet.CGImage, rect)] ];
            }
         }
    }
}

Compiled the above code with ARC enabled. The Analyze tool reports a possible memory leak since imageWithCGImage:: returns UIImage with count +1, then reference is lost. Leaks Instrument reports no memory leaks at all. Whats going on here?

Furthermore, since ARC prohibits use of manually using release ect, how does one fix the leak?

Thanks to anyone who can offer any advice.

回答1:

ARC does not manage C-types, of which CGImage may be considered. You must release the ref manually when you are finished with CGImageRelease(image);

+(void)setup {
    UIImage* spriteSheet = [UIImage imageNamed:@"mySpriteSheet.png"];
    CGRect rect;
    animation = [NSMutableArray arrayWithCapacity:numberOfFramesInSpriteSheet];
    int frameCount = 0;

    for (int row = 0; row < numberFrameRowsInSpriteSheet; row++) {
        for (int col = 0; col < numberFrameColsInSpriteSheet; col++) {
            frameCount++;
            if (frameCount <= numberOfFramesInSpriteSheet) {
                rect = CGRectMake(col*frameHeight, row*frameWidth, frameHeight, frameWidth);
                //store our image ref so we can release it later
                //The create rule says that any C-interface method with "create" in it's name 
                //returns a +1 foundation object, which we must release manually.
                CGImageRef image = CGImageCreateWithImageInRect(spriteSheet.CGImage, rect)
                //Create a UIImage from our ref.  It is now owned by UIImage, so we may discard it.
                [animation addObject:[UIImage imageWithCGImage:image]];
                //Discard the ref.  
                CGImageRelease(image);
            }
         }
    }
}

回答2:

None of the core foundation data structure is dealt with ARC. Many a times this creates a problem. In these case we have to manually release the memory.