Iphone 从AFImageRequestOperation中的成功块返回图像

我正在尝试编写一个方便的函数，该函数将接受图像标识符，并使用AFNetworking的AFImageRequestOperation下载图像。该函数正确下载图像，但我无法在成功块中返回UIImage

-(UIImage *)downloadImage:(NSString*)imageIdentifier
{
  NSString* urlString = [NSString stringWithFormat:@"http://myserver.com/images/%@", imageIdentifier];

  AFImageRequestOperation* operation = [AFImageRequestOperation imageRequestOperationWithRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:urlString]] imageProcessingBlock:nil
  success:^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image)
  {
    NSLog(@"response: %@", response);
    return image;                                                   
  }
  failure:nil];

[operation start];

}

返回图像行显示错误：

Incompatible block pointer types sending 'UIImage *(^)(NSURLRequest *__strong, NSHTTPURLResponse *__strong, UIImage *__strong)' to parameter of type 'void (^)(NSURLRequest *__strong, NSHTTPURLResponse *__strong, UIImage *__strong)' 

你知道发生了什么事吗？我很想打电话给你

UIImage*photo=[下载图像：id_12345]
网络映像下载操作是异步的，您不能在操作开始时分配它

您试图构建的函数应该使用委托或块

- (void)downloadImageWithCompletionBlock:(void (^)(UIImage *downloadedImage))completionBlock identifier:(NSString *)identifier {
  NSString* urlString = [NSString stringWithFormat:@"http://myserver.com/images/%@", identifier];

  AFImageRequestOperation* operation = [AFImageRequestOperation imageRequestOperationWithRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:urlString]] imageProcessingBlock:nil
  success:^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image)
  {
    NSLog(@"response: %@", response);
    completionBlock(image);                                                   
  }
  failure:nil];

  [operation start];
}

这样说吧

// start updating download progress UI
[serverInstance downloadImageWithCompletionBlock:^(UIImage *downloadedImage) {
  myImage = downloadedImage;
  // stop updating download progress UI
} identifier:@""];