[英]Create CGImage From CGBitmapContext and Add to UIImageView
我正在尝试通过创建CGBitMapContext创建UICollectionViewCell的快照。 我尚不清楚如何执行此操作或如何使用关联的类,但是经过一番研究,我编写了以下方法,该方法是从UICollectionViewCell子类内部调用的:
- (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);
}
结果是该图像没有出现。 调试后,我可以确定我具有有效的(非nil)上下文,CGImage,UIImage和UIImageView,但是屏幕上没有任何显示。 有人可以告诉我我想念什么吗?
您可以将其添加为UIView的类别,任何视图均可访问
- (UIImage*) snapshot
{
UIGraphicsBeginImageContextWithOptions(self.frame.size, YES /*opaque*/, 0 /*auto scale*/);
[self.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage* image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return image;
}
然后,您只需要从单元格对象执行[self addSubview:[[UIImageView alloc] initWithImage:self.snapshot]]
。
[编辑]
如果需要异步渲染(完全可以理解),则可以使用调度队列来实现。 我认为这会起作用:
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);
});
});
}
[编辑]
- (void) execute
{
__weak typeof(self) weakSelf = self;
[self snapshotAsync:^(UIImage* image) {
[weakSelf addSubview:[[UIImageView alloc] initWithImage:image]]
}];
}
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