ios 如何在没有完成块的情况下在 NSURLSession 中获取服务器响应数据

How to get server response data in NSURLSession without completion block

提问by Rob

I am using NSURLSessionfor background image uploading. And according to uploaded image my server gives me response and I do change in my app accordingly. But I can't get my server response when my app uploading image in background because there is no completion block.

我正在使用NSURLSession背景图片上传。根据上传的图片，我的服务器给了我响应，我会相应地更改我的应用程序。但是当我的应用程序在后台上传图像时，我无法获得服务器响应，因为没有完成块。

Is there way to get response without using completion block in NSURLUploadTask?

有没有办法在不使用完成块的情况下获得响应NSURLUploadTask？

Here is my code :

这是我的代码：

 self.uploadTask = [self.session uploadTaskWithRequest:request fromData:body completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
            NSString *returnString = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
            NSLog(@"returnString : %@",returnString);
            NSLog(@"error : %@",error);
        }];
 [self.uploadTask resume];

But i got this error..

但我得到了这个错误..

Terminating app due to uncaught exception 'NSGenericException', reason: 'Completion handler blocks are not supported in background sessions. Use a delegate instead.'

由于未捕获的异常“NSGenericException”而终止应用程序，原因：“后台会话中不支持完成处理程序块。改用委托。

But if I can't use completion handler than how should I get the server response. It says use delegate but I can't find any delegate method which can gives me server response.

但是如果我不能使用完成处理程序，那么我应该如何获得服务器响应。它说使用委托，但我找不到任何可以为我提供服务器响应的委托方法。

回答by Rob

A couple of thoughts:

一些想法：

First, instantiate your session with a delegate, because background sessions must have a delegate:

首先，使用 a 实例化您的会话delegate，因为后台会话必须有一个委托：

NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration backgroundSessionConfigurationWithIdentifier:kSessionIdentifier];
self.session = [NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:nil];

Second, instantiate your NSURLSessionUploadTaskwithout a completion handler, because tasks added to a background session cannot use completion blocks. Also note, I'm using a file URL rather than a NSData:

其次，在NSURLSessionUploadTask没有完成处理程序的情况下实例化您，因为添加到后台会话的任务不能使用完成块。另请注意，我使用的是文件 URL 而不是NSData：

NSURLSessionTask *task = [self.session uploadTaskWithRequest:request fromFile:fileURL];
[task resume];

Third, implement the relevant delegate methods. At a minimum, that might look like:

第三，实现相关的委托方法。至少，这可能看起来像：

- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveData:(NSData *)data {
    NSMutableData *responseData = self.responsesData[@(dataTask.taskIdentifier)];
    if (!responseData) {
        responseData = [NSMutableData dataWithData:data];
        self.responsesData[@(dataTask.taskIdentifier)] = responseData;
    } else {
        [responseData appendData:data];
    }
}

- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error {
    if (error) {
        NSLog(@"%@ failed: %@", task.originalRequest.URL, error);
    }

    NSMutableData *responseData = self.responsesData[@(task.taskIdentifier)];

    if (responseData) {
        // my response is JSON; I don't know what yours is, though this handles both

        NSDictionary *response = [NSJSONSerialization JSONObjectWithData:responseData options:0 error:nil];
        if (response) {
            NSLog(@"response = %@", response);
        } else {
            NSLog(@"responseData = %@", [[NSString alloc] initWithData:responseData encoding:NSUTF8StringEncoding]);
        }

        [self.responsesData removeObjectForKey:@(task.taskIdentifier)];
    } else {
        NSLog(@"responseData is nil");
    }
}

Note, the above is taking advantage of a previously instantiated NSMutableDictionarycalled responsesData(because, much to my chagrin, these "task" delegate methods are done at the "session" level).

请注意，以上是利用先前实例化的NSMutableDictionary调用responsesData（因为令我懊恼的是，这些“任务”委托方法是在“会话”级别完成的）。

Finally, you want to make sure to define a property to store the completionHandlerprovided by handleEventsForBackgroundURLSession:

最后，您要确保定义一个属性来存储completionHandler提供的handleEventsForBackgroundURLSession：

@property (nonatomic, copy) void (^backgroundSessionCompletionHandler)(void);

And obviously, have your app delegate respond to handleEventsForBackgroundURLSession, saving the completionHandler, which will be used below in the URLSessionDidFinishEventsForBackgroundURLSessionmethod.

显然，让您的应用程序委托响应handleEventsForBackgroundURLSession，保存completionHandler，这将在下面的URLSessionDidFinishEventsForBackgroundURLSession方法中使用。

- (void)application:(UIApplication *)application handleEventsForBackgroundURLSession:(NSString *)identifier completionHandler:(void (^)())completionHandler {
    // This instantiates the `NSURLSession` and saves the completionHandler. 
    // I happen to be doing this in my session manager, but you can do this any
    // way you want.

    [SessionManager sharedManager].backgroundSessionCompletionHandler = completionHandler;
}

And then make sure your NSURLSessionDelegatecalls this handler on the main thread when the background session is done:

然后确保NSURLSessionDelegate在后台会话完成后在主线程上调用此处理程序：

- (void)URLSessionDidFinishEventsForBackgroundURLSession:(NSURLSession *)session {
    if (self.backgroundSessionCompletionHandler) {
        dispatch_async(dispatch_get_main_queue(), ^{
            self.backgroundSessionCompletionHandler();
            self.backgroundSessionCompletionHandler = nil;
        });
    }
}

This is only called if some of the uploads finished in the background.

仅当某些上传在后台完成时才会调用。

There are a few moving parts, as you can see, but that's basically what's entailed.

正如您所看到的，有一些活动部分，但这基本上是必需的。