uiimage - Another iPhone - CGBitmapContextCreateImage Leak

Question

Like in this post:

• iPhone - UIImage Leak, ObjectAlloc Building

I'm having a similar problem. The pointer from the malloc in create_bitmap_data_provider is never freed. I've verified that the associated image object is eventually released, just not the provider's allocation. Should I explicitly create a data provider and somehow manage it's memory? Seems like a hack.

CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef context = CGBitmapContextCreate(NULL, blah blah blah);
CGColorSpaceRelease(colorSpace);

// ... draw into context

CGImageRef imageRef = CGBitmapContextCreateImage(context);
UIImage * image = [[UIImage alloc] initWithCGImage:imageRef];

CGImageRelease(imageRef);
CGContextRelease(context);

---

After fbrereto's answer below, I changed the code to this:

- (UIImage *)modifiedImage {
    CGSize size = CGSizeMake(width, height);

    UIGraphicsBeginImageContext(size);
    CGContextRef context = UIGraphicsGetCurrentContext();

    // draw into context   

    UIImage * image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return image;  // image retainCount = 1
}    

// caller: 
{
    UIImage * image = [self modifiedImage]; 
    _imageView.image = image; // image retainCount = 2
}

// after caller done, image retainCount = 1, autoreleased object lost its scope

Unfortunately, this still exhibits the same issue with a side effect of flipping the image horizontally. It appears to do the same thing with CGBitmapContextCreateImage internally.

I have verified my object's dealloc is called. The retainCount on the _imageView.image and the _imageView are both 1 before I release the _imageView. This really doesn't make sense. Others seem to have this issue as well, I'm the last one to suspect the SDK, but could there be an iPhone SDK bug here???

Answer 1

It looks like the problem is that you are releasing a pointer to the returned CGImage, rather than the CGImage itself. I too was having similar issues before with continual growing allocations and an eventual app crash. I addressed it by allocating a CGImage rather than a CGImageRef. After the changes run your code in Insturments with allocations, and you should not see anymore perpetual memory consumption from malloc. As well if you use the class method imageWithCGImage you will not have to worry about autoreleasing your UIImage later on.

I typed this on a PC so if you drop it right into XCode you may have syntax issue, I appologize in advance; however the principal is sound.

CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); 
CGContextRef context = CGBitmapContextCreate(NULL, blah blah blah); 
CGColorSpaceRelease(colorSpace);

// ... draw into context  

CGImage cgImage = CGBitmapContextCreateImage(context); 
UIImage * image = [UIImage imageWithCGImage:cgImage];  
CGImageRelease(cgImage); 
CGContextRelease(context);
return image;