CoreGraphics object autoreleased too many times

Question

Upon analyzing my app, Xcode gave me an alert showing that their was a potential leak of an object stored into 'colorSpace' (last line of the code below):

CGContextSaveGState(context);
CGContextAddRect(context, rect);
CGContextClip(context);
CGContextDrawLinearGradient(context, gradient, startPoint, endPoint, 0);
CGContextRestoreGState(context);

So, I added the following line:

CFAutorelease(context);

And analyzed again. This time, I got an alert in the second line below of "object autoreleased too many times (within a call to 'CGPointMake'):

case SWShadowDirectionUp:
     startPoint = CGPointMake(CGRectGetMinX(rect), CGRectGetMaxY(rect) - 0.5);
     endPoint = CGPointMake(CGRectGetMaxX(rect), CGRectGetMaxY(rect) - 0.5);
                break;

Below is where the colorSpace variable is used:

CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGFloat locations[] = { 0.0, 1.0 };
NSArray *colors = @[ (__bridge id)self.startColor.CGColor, (__bridge id)self.endColor.CGColor ];
CGGradientRef gradient = CGGradientCreateWithColors(colorSpace, (__bridge CFArrayRef)colors, locations);
CFAutorelease(colorSpace);

However, I'm not sure what exactly is going wrong, or how to fix it. Does anyone have any suggestions?

Answer 1

I'm unsure what you've done wrong in your source because you haven't included the entire scope of colorSpace . Here is what I have tried and the static analyzer does not complain:

- (UIImage *)decompressImage:(UIImage *)image {
  CGImageRef imageRef = image.CGImage;
  size_t width = CGImageGetWidth(imageRef);
  size_t height = CGImageGetHeight(imageRef);

  CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
  CGContextRef context = CGBitmapContextCreate(NULL, width, height, 8,
                                               width * 4, colorSpace,
                 kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Little);
  CGColorSpaceRelease(colorSpace);
  if (!context)
    return image;

  CGContextDrawImage(context, CGRectMake(0.0f, 0.0f, width, height), imageRef);
  CGImageRef decompressedImageRef = CGBitmapContextCreateImage(context);
  CGContextRelease(context);

  UIImage *decompressedImage = [UIImage imageWithCGImage:decompressedImageRef scale:image.scale orientation:image.imageOrientation];
  CGImageRelease(decompressedImageRef);
  return decompressedImage;
}

Just make sure you have a Release for every Create before the end of the scope.