Question

I have an class method which generates a UIImage, like this:

+ (UIImage*)imageWithFileName:(NSString*)imgFile {
    UIImage *img = nil;

    NSBundle *appBundle = [NSBundle mainBundle];
    NSString *resourcePath = [appBundle pathForResource:imgFile ofType:nil];

    if (resourcePath != nil) {
        NSURL *imageURL = [NSURL fileURLWithPath:resourcePath];
        NSData *data = [[NSData alloc] initWithContentsOfURL:imageURL];

        img = [UIImage imageWithData:data]; // should be autoreleased!!

        [data release];
    }

    return img;
}

However, when I use this, the image data is NEVER freed. There is definitely a memory bug with this, although I didn’t break any memory management rule I am aware of. My guess is that because this is a class method which gets called from instance methods, There is no active autorelease pool in place or it’s one that only gets drained when I quit the app. Could that be right?

Answer 1

The real question I think is, how are you measuring that the memory is not released.

Autorelease pools are all related to the thread and runloop you are in – because they free memory when a call returns all the way to the main runloop. It doesn’t matter if you are calling a class method or an instance method or even a C function, autorelease will work the same in all cases.

I know in your testing you found there are differences, but simply put if you see a difference it is for some other reason – because autorelease always works the same across the system as far as freeing memory if you are in the same runloop.