Question

我们的应用使用didReceiveRemoteNotification: fetchCompletionHandler:方法UIApplicationDelegate在收到content-available推送通知时开始下载。

应用程序采取的各个步骤：

[1]收到通知

- (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

- (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;
}];

这会产生如下日志：

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：

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，下载永远不会完成，看起来应用程序会冻结其后台会话。因为当我将应用程序放回到前台时，下载将在某个时刻完成。

之前有没有人见过这种行为？仅供参考：我启用了正确的功能，使用了正确的配置文件，应用程序有权在后台运行。

更新我们在开发后台管理器时使用AFNetworking 2.0 and background transfers中的答案/评论

Answer 1

您在开始下载时调用完成处理程序！我非常确定你应该在下载完成后调用完成处理程序，而不是在下载开始后2秒！换句话说，你应该在completionHandler(UIBackgroundFetchResultNewData);内调用self setDownloadTaskDidFinishDownloadingBlock...，并且corse以某种方式传递CompletionBlock。

[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：

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

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

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

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

didReceiveRemoteNotification：fetchCompletionHandler：下载冻结

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