iphone - 从 AFImageRequestOperation 中的成功 block 返回图像

Question

我正在尝试编写一个方便的函数，它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 block 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];

}

return image; 行给了我错误:

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

对发生的事情有什么想法吗？我很乐意打电话

UIImage* 照片 = [downloadImage:id_12345];

Answer 1

AFNetworking 图像下载操作是异步的，您无法在操作开​​始时对其进行分配。

您尝试构建的函数应该使用委托(delegate)或 block 。

- (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];
}

这样称呼

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