ios-AFImageRequestOperation返回圖片

AFImageRequestOperation返回圖片

要寫一個應用，用來接受圖片標示符，並且使用 AFNetworking 的 AFImageRequestOperation 下載圖片。

目前下載已經成功了，但是在block中無法返回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];

}

其中return image;這行報錯：

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

我希望能調用：

UIImage* photo = [downloadImage:id_12345];

最佳回答：

AFNetworking圖片下載操作是異步的，你不能在操作開始的時候指定它。

你構建的函數應該用delegates和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];
}

如下調用：

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