如何将多个 UIImageView 合并为一个 UIImage

我有 2 个 UIImageViews 彼此叠放（图片 + 覆盖框架），我想将它们作为 1 张图片保存到相机胶卷中。

我应该如何组合这 2 个 UIImageView，以便我可以使用“结果”UIImage 调用 UIImageWriteToSavedPhotosAlbum 函数？

+ (UIImage * ) mergeImage: (UIImage *) imageA
                                 withImage:  (UIImage *) imageB
                                 strength: (float) strength {

UIGraphicsBeginImageContextWithOptions(CGSizeMake(imageA.size.width, imageA.size.height), YES, 0.0); 

[imageA drawAtPoint: CGPointMake(0,0)];

[imageB drawAtPoint: CGPointMake(0,0) 
          blendMode: kCGBlendModeNormal // you can play with this
              alpha: strength]; // 0 - 1

UIImage *answer = UIGraphicsGetImageFromCurrentImageContext(); 
UIGraphicsEndImageContext();
return answer; }