【问题标题】：How to return the ouput if method is using NSURLConnection Asynchronous calls with blocks如何返回方法的输出是使用带有块的 NSURLConnection 异步调用
【发布时间】：2014-04-23 18:18:21
【问题描述】：

我正在使用 NSURLConnection 块方法向服务器发送请求以获取响应。我无法在块中使用 return YES 或 return NO。我该如何解决这个问题？

-(BOOL)checkForValidUrl:(NSString *)url
{
       __block int httpStatus=0;
        NSMutableURLRequest *request=[[NSMutableURLRequest alloc]initWithURL:[NSURL URLWithString:url]];
        [request setValue:@"application/json" forHTTPHeaderField:@"content-type"];
        [request setValue:@"application/json" forHTTPHeaderField:@"Accept"];


        [NSURLConnection sendAsynchronousRequest:request
                                           queue:[NSOperationQueue mainQueue]
                               completionHandler:^(NSURLResponse *response, NSData *responseData, NSError *error)
         {
            httpStatus = [((NSHTTPURLResponse *)response) statusCode];
             NSLog(@"httpStatus inside block:%d",httpStatus);


         }
         ];

        return NO;
}

【问题讨论】：

标签： ios ios5 asynchronous nsurlconnection objective-c-blocks

【解决方案1】：

不返回任何内容，而是传递一个完成块，该块稍后会通知调用者检查结果。您将不得不重新编写调用代码以不需要立即获得结果。

例如，假设 200 响应意味着 URL 有效：

-(void)checkForValidUrl:(NSString *)url completion:(void (^)(BOOL validURL))completion {
  __block int httpStatus=0;
  NSMutableURLRequest *request=[[NSMutableURLRequest alloc]initWithURL:[NSURL URLWithString:url]];
  [request setValue:@"application/json" forHTTPHeaderField:@"content-type"];
  [request setValue:@"application/json" forHTTPHeaderField:@"Accept"];


  [NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue]
    completionHandler:^(NSURLResponse *response, NSData *responseData, NSError *error) {
      httpStatus = [((NSHTTPURLResponse *)response) statusCode];
      NSLog(@"httpStatus inside block:%d",httpStatus);

      completion(200 == httpStatus);
    }
  ];
}

【讨论】：

【解决方案2】：

没有办法。应用调用return语句时，连接结果未知。你应该使用类似的东西

[NSURLConnection sendAsynchronousRequest:request
                                   queue:[NSOperationQueue mainQueue]
                        completionHandler:^(NSURLResponse *response, NSData *responseData, NSError *error)
         {
            httpStatus = [((NSHTTPURLResponse *)response) statusCode];
             NSLog(@"httpStatus inside block:%d",httpStatus);

           [_your_delegate_object connectionFinishedWithStatus:httpStatus data:responseData];

         }
         ];

【讨论】：

【解决方案3】：

应该是这样的

-(void)checkForValidUrl:(NSString *)url completion:(void(^)(BOOL success))completion {
    __block int httpStatus=0;
    NSMutableURLRequest *request=[[NSMutableURLRequest alloc]initWithURL:[NSURL URLWithString:url]];
    [request setValue:@"application/json" forHTTPHeaderField:@"content-type"];
    [request setValue:@"application/json" forHTTPHeaderField:@"Accept"];

    [NSURLConnection sendAsynchronousRequest:request
                                       queue:[NSOperationQueue mainQueue]
                           completionHandler:^(NSURLResponse *response, NSData *responseData, NSError *error)
     {
        httpStatus = [((NSHTTPURLResponse *)response) statusCode];
        NSLog(@"httpStatus inside block:%d",httpStatus);
        completion(httpStatus == 200) //if Yes or No depends on the status

     }
     ];
}

【讨论】：

【解决方案4】：

您的 DataFetchController.h 文件

- (void)beginLeadTaskWithCallbackBlock:(void (^)(NSArray *))callbackBlock;

您的 DataFetchController.m 文件

-(void)beginLeadTaskWithCallbackBlock:(void (^)(NSArray *))callbackBlock{


// add your post code here


   [NSURLConnection sendAsynchronousRequest:request queue:queue completionHandler:^(NSURLResponse *response, NSData *data, NSError *error)

    {
         NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response;
         if ([data length] >0 && error == nil && [httpResponse statusCode] == 200)
         {


             NSArray *dictionary = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:&error];


             NSLog(@"data %@",dictionary);
             callbackBlock(dictionary);

         }

     }];

}

阻止调用你的视图控制器

避免内存泄漏的弱使用

 DataFetchController *getFetch=[[DataFetchController alloc]init];
 DataFetchController * __weak weakDataFetch=getFetch;
    [weakDataFetch beginLeadTaskWithCallbackBlock:^(NSArray *mm){



        dispatch_async(dispatch_get_main_queue(), ^{

        //update main UI 

        });

    }];

【讨论】：