Create CGImage From CGBitmapContext and Add to UIImageView - objective-c

Question

I am trying to create a snapshot of a UICollectionViewCell by creating a CGBitMapContext. I am not entirely clear on how to do this or how to use the associated classes, but after a bit of research, I have written the following method which is called from inside my UICollectionViewCell subclass:
- (void)snapShotOfCell
{
float scaleFactor = [[UIScreen mainScreen] scale];
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef context = CGBitmapContextCreate(NULL, self.frame.size.width * scaleFactor, self.frame.size.height * scaleFactor, 8, self.frame.size.width * scaleFactor * 4, colorSpace, kCGImageAlphaPremultipliedFirst);
CGImageRef image = CGBitmapContextCreateImage(context);
UIImage *snapShot = [[UIImage alloc]initWithCGImage:image];
UIImageView *imageView = [[UIImageView alloc]initWithFrame:self.frame];
imageView.image = snapShot;
imageView.opaque = YES;
[self addSubview:imageView];
CGImageRelease(image);
CGContextRelease(context);
CGColorSpaceRelease(colorSpace);
}
The result is that the image does not appear. Upon debugging, I can determine that I have a valid (non nil) context, CGImage, UIImage and UIImageView, but nothing appears onscreen. Can someone tell me what I am missing?

Answer 1

You can add this as a category to UIView and it will be accessible for any view
- (UIImage*) snapshot
{
UIGraphicsBeginImageContextWithOptions(self.frame.size, YES /*opaque*/, 0 /*auto scale*/);
[self.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage* image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return image;
}
Then you just need to do [self addSubview:[[UIImageView alloc] initWithImage:self.snapshot]] from you cell object.
[EDIT]
Providing the need for asynchronous rendering (totally understandable) this can be achieved using dispatch queues. I think this would work:
typedef void(^ImageOutBlock)(UIImage* image);
- (void) snapshotAsync:(ImageOutBlock)block
{
CGFloat scale = [[UIScreen mainScreen] scale];
CALayer* layer = self.layer;
CGRect frame = self.frame;
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^() {
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef context = CGBitmapContextCreate(NULL, frame.size.width * scaleFactor, frame.size.height * scaleFactor, 8, frame.size.width * scaleFactor * 4, colorSpace, kCGImageAlphaPremultipliedFirst);
UIGraphicsBeginImageContextWithOptions(frame.size, YES /*opaque*/, scale);
[layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage* image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
CGContextRelease(context);
CGColorSpaceRelease(colorSpace);
dispatch_async(dispatch_get_main_queue(), ^() {
block(image);
});
});
}
[EDIT]
- (void) execute
{
__weak typeof(self) weakSelf = self;
[self snapshotAsync:^(UIImage* image) {
[weakSelf addSubview:[[UIImageView alloc] initWithImage:image]]
}];
}