Question

Xcode Analyze complained that I incorrectly decremented ref count at the line marked “this line”. it seems a bit strange, since it was not obvious that that line decrements the ref count.

- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    UIImage * image = [[UIImage alloc] initWithData:receivedData];
    if (image == nil) {
        image = [UIImage imageNamed:@"null.bmp"];
    }
    self.itemImage.image = image; //this line
    self.promotion.image = image; 
    [image release];
}

Answer 1

This is a mildly tricky thing; it’s understandable that it is causing confusion. The two paths here result in image holding objects with different ownership statuses, and thus different reference counts.

Going through the if results in image holding an object that your code doesn’t own.

UIImage * image = [[UIImage alloc] initWithData:receivedData];
// If |initWithData:| succeeds, the object in |image| is owned, because you
// called |alloc| to create it.
if (image == nil) {
    image = [UIImage imageNamed:@"null.bmp"];
    // This object is _not_ owned by your code and you must not send
    // |release| to it.
}
// ... the setter lines are irrelevant to the reference count of |image|.

[image release];
// This is only okay if |initWithData:| succeeded and you have ownership
// of |image|.

I think that the analyzer is indicating the wrong line, in the same way the compiler will complain about a missing semicolon five lines later.

The way to solve this may be to retain the image you get from imageNamed: You can’t just not send release, because you do own image in one case, and you need to properly relinquish that ownership. I’d also suggest putting a comment in there about sending retain so you remember eight months later why you did it.

Better than that, as suggested below by the inimitable Bavarious, and as I think you yourself already figured out, would be to autorelease the alloc‘d image and remove the later release line.