didReceiveRemoteNotification：fetchCompletionHandler：下载冻结 [英] didReceiveRemoteNotification: fetchCompletionHandler: download freezes

问题描述

我们的应用程序利用 didReceiveRemoteNotification：fetchCompletionHandler：方法 UIApplicationDelegate 在时开始下载收到内容可用推送通知。

Our app utilizes didReceiveRemoteNotification: fetchCompletionHandler: methods UIApplicationDelegate to start a download when a content-available push notification is received.

应用执行的各个步骤：

[1]接收通知

- (void)application:(UIApplication *)application didReceiveRemoteNotification:(NSDictionary *)userInfo fetchCompletionHandler:(void (^)(UIBackgroundFetchResult result))completionHandler {
    NSLog(@"Remote download push notification received");
    [AFHTTPSessionManager_Instance downloadFile:completionHandler];        
}

[2]开始新的下载任务

[2] Start a new download Task

- (void)downloadFile:(void (^)(UIBackgroundFetchResult))completionHandler {
    NSURLSessionDownloadTask *task = [AFHTTPSessionManager_Instance downloadTaskWithRequest:request progress:nil destination:nil completionHandler:nil];
    [task resume];
    NSLog(@"Starting download of %@", request.URL.absoluteString);

    // Some additional time to start the download
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 2 * NSEC_PER_SEC), dispatch_get_main_queue(), ^{
        NSLog(@"Completion handler!");
        completionHandler(UIBackgroundFetchResultNewData);
});

[3]处理下载

[self setDownloadTaskDidFinishDownloadingBlock:^NSURL *(NSURLSession *session, NSURLSessionDownloadTask *downloadTask, NSURL *location) {
  NSLog(@"Download complete!");
  // ... Create save path
  return path;
}];

这将生成如下日志：

2015-09-21 15:38:57.145 App[315:20933] Remote download push notification received
2015-09-21 15:38:57.485 App[315:20933] Starting download of http://domain.com/file.mov
2015-09-21 15:38:59.654 App[315:20933] Completion handler!
2015-09-21 15:39:06.315 App[315:20933] Download complete!

但有时（完全随机），我看到这样的日志：

But sometimes (completely random) I see logs like this:

2015-09-21 15:38:57.145 App[315:20933] Remote download push notification received
2015-09-21 15:38:57.485 App[315:20933] Starting download of http://domain.com/file.mov
2015-09-21 15:38:59.654 App[315:20933] Completion handler!

换句话说，下载从未完成，看来该应用程序冻结了其后台会话。因为当我将应用重新放到前台时，下载会在某个时候完成。

In other words the download never completes, it looks like the app freezes its background session. Because when I put the app back into the foreground the download will finish at some point.

有人以前见过这种行为吗？

仅供参考：启用了正确的功能，使用了正确的配置文件，并且该应用有权在后台运行。

Has anyone seen this behavior before?
FYI: I enabled the right capabilities, used a correct provision profile and the app has permissions to run in the background.

更新：
我们开发背景时，在 AFNetworking 2.0和背景传输中使用了答案/评论经理

Update: We've used answers/comments in AFNetworking 2.0 and background transfers when developing the background manager

推荐答案

您要在开始下载时调用完成处理程序！我很确定您应该在下载完成后（而不是下载开始后的2秒内）致电完成处理程序！换句话说，您应该在 self setDownloadTaskDidFinishDownloadingBlock ... 内部调用 completionHandler（UIBackgroundFetchResultNewData）; ，然后通过CompletionBlock

You are calling the completion handler upon starting download! I'm pretty sure you should call the completion handler when the download is finished not 2 seconds after download started! in other words, you should call completionHandler(UIBackgroundFetchResultNewData); inside self setDownloadTaskDidFinishDownloadingBlock... and of corse pass the CompletionBlock somehow.

[self setDownloadTaskDidFinishDownloadingBlock:^NSURL *(NSURLSession *session, NSURLSessionDownloadTask *downloadTask, NSURL *location) {

  NSLog(@"Download complete!");
  // ... Create save path
 NSLog(@"Completion handler!");
 completionHandler(UIBackgroundFetchResultNewData);

  return path;
}];

正确的日志应该是这样的：

The correct log should be something like this:

2015-09-21 15：38：57.145 App [315：20933]远程下载推送
收到通知

2015-09-21 15:38:57.145 App[315:20933] Remote download push notification received

2015-09-21 15：38：57.485 App [315：20933]开始下载
http：// domain.com/file.mov

2015-09-21 15:38:57.485 App[315:20933] Starting download of http://domain.com/file.mov

2015-09-21 15：38：59.654 App [315：20933]下载完成！

2015-09-21 15:38:59.654 App[315:20933] Download complete!

2015-09-21 15：39：06.315 App [315：20933]完成处理程序！

2015-09-21 15:39:06.315 App[315:20933] Completion handler!

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