ios实现截屏

第一种截屏：

    CGImageRef UIGetScreenImage();
    CGImageRef img = UIGetScreenImage();
    UIImage *scImage = [UIImage imageWithCGImage:img];
    UIImageWriteToSavedPhotosAlbum(scImage, nil, nil, nil);

第二种截屏：

- (UIImage *)imageFromView
{
    
    UIGraphicsBeginImageContext(self.view.frame.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    [self.view.layer renderInContext:context];
    UIImage *theImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    
    return theImage;
}

但是不能在相机界面截图，截取出来的图片是空白的。