What's the right memory management pattern for buffer->CGImageRef->UIImage?

Question

I have a function that takes some bitmap data and returns a UIImage * from it. It looks something like so:

UIImage * makeAnImage() 
{
    unsigned char * pixels          


        

Answer 1

The thumb rule here is "-release* it if you don't need it".

Because you no longer need provider and imageRef afterwards, you should -release all of them, i.e.

UIImage * image =  [[UIImage alloc] initWithCGImage:imageRef];
CGDataProviderRelease(provider);
CGImageRelease(imageRef);
return [image autorelease];

pixel is not managed by ref-counting, so you need to tell the CG API to free them for you when necessary. Do this:

void releasePixels(void *info, const void *data, size_t size) {
   free((void*)data);
}
....

CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, pixels, pixelBufferSize, releasePixels);

By the way, you can use +imageWithCGImage: instead of [[[* alloc] initWithCGImage:] autorelease]. Even better, there is +imageWithData: so you don't need to mess with the CG and malloc stuff.

(*: Except when the retainCount is already supposedly zero from the beginning.)