OC代码如下
- (UIImage *)captureScreen:(UIView *)mView size:(CGSize)mSize {
// Creates a bitmap-based graphics context and makes it the current context
//创建一个位图，并成为当前的背景
UIGraphicsBeginImageContext(mSize);
// Renders the receiver and its sublayers into the specified context
//渲染给子layer提供一个特定的背景
[mView.layer renderInContext:UIGraphicsGetCurrentContext()];
// Returns an image based on the contents of the current bitmap-based graphics context
//返回一个当前背景下的位图
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
// Removes the current bitmap-based graphics context from the top of the stack
//讲当前位图从堆中移除
UIGraphicsEndImageContext();
return image;
}