NSURLSessionConfiguration backgroundSessionConfigurationWithIdentifier : 应用程序被推入后台后下载停止

Question

1. 此方法设置背景对象。

   - (void) downloadWithURL: (NSMutableArray *)urlArray
                pathArr: (NSMutableArray *)pathArr
              mediaInfo: (MediaInfo *)mInfo
   {
       bgDownloadMediaInfo = mInfo;
       reqUrlCount = urlArray.count;
       dict = [NSDictionary dictionaryWithObjects:pathArr
                                      forKeys:urlArray];
       mutableDictionary = [dict mutableCopy];
       backgroundConfigurationObject = [NSURLSessionConfiguration backgroundSessionConfigurationWithIdentifier:@"XXXXX"];
       backgroundConfigurationObject.sessionSendsLaunchEvents = YES;
       backgroundConfigurationObject.discretionary = YES;
       backgroundSession = [NSURLSession sessionWithConfiguration: backgroundConfigurationObject
                                                     delegate: self delegateQueue: [NSOperationQueue currentQueue]];
       self.requestUrl = [urlArray objectAtIndex:0];
       download = [backgroundSession downloadTaskWithURL:self.requestUrl];
       [download resume];
   
   }
   

2. 这些是完成处理程序。

   #pragma Mark - NSURLSessionDownloadDelegate
   
   - (void)URLSession: (NSURLSession *)session
         downloadTask: (NSURLSessionDownloadTask *)downloadTask
   didFinishDownloadingToURL: (NSURL *)location
   {
     LogDebug(@"Download complete for request url (%@)", downloadTask.currentRequest.URL);
     NSString *temp = [mutableDictionary objectForKey:downloadTask.currentRequest.URL];
     NSString *localPath = [NSString stringWithFormat: @"%@",temp];
     NSFileManager *fileManager = [NSFileManager defaultManager];
     NSURL *destinationURL = [NSURL fileURLWithPath: localPath];
     NSError *error = nil;
     [fileManager moveItemAtURL:location toURL:destinationURL error:&error];
     LogDebug(@"Moving download file at url : (%@) to : (%@)", downloadTask.currentRequest.URL, destinationURL);
     reqUrlCount --;
     downloadSegment ++;
     // Handover remaining download requests to the OS
     if ([finalUrlArr count] != 0) {
       // remove the request from the array that got downloaded.
       [finalUrlArr removeObjectAtIndex:0];
       [finalPathArr removeObjectAtIndex:0];
       if ([finalUrlArr count] > 0) {
         // proceed with the next request on top.
         self.requestUrl = [finalUrlArr objectAtIndex:0];
         download = [backgroundSession downloadTaskWithURL:self.requestUrl];
         [download resume];
       }
     }
     if ([adsArray count] > 0) {
       adsArrayCount --;
       // delegate back once all the ADs segments have been downloaded.
       if (adsArrayCount == 0) {
         for (int i = 0; i < [adsArray count]; i++) {
           NSArray *ads = [adsArray objectAtIndex: i];
           for (int j = 0; j < [ads count]; j++) {
             MediaInfo *ad = [ads objectAtIndex: j];
             [self setDownloadComplete: ad];
             // skip sending downloadFinish delegate if the media is marked as downloadDone
             if (!ad.downloadDone) {
               [delegate MediaDownloadDidFinish: ad.mediaId error: NO];
             }
             ad.downloadDone = YES;
           }
         }
         downloadSegment = 0;
       }
     }
   
     // delegate back once all the main media segments have been downloaded.
     if (reqUrlCount == 0) {
       [self setDownloadComplete: mediaInfo];
       state = DownloadState_Done;
       // skip sending downloadFinish delegate if the media is marked as downloadDone
       if (!bgDownloadMediaInfo.downloadDone) {
         [delegate MediaDownloadDidFinish: bgDownloadMediaInfo.mediaId error: NO];
       }
       bgDownloadMediaInfo.downloadDone = YES;
       [urlArr release];
       [pathArr release];
       [finalUrlArr release];
       [finalPathArr release];
       // invalidate the NSURL session once complete
       [backgroundSession invalidateAndCancel];
     }
   }
   
   
   
   - (void)URLSession: (NSURLSession *)session
                 task: (NSURLSessionTask *)task
   didCompleteWithError: (NSError *)error
   {
     if (error) {
       NSLog(@"Failure to download request url (%@) with error (%@)", task.originalRequest.URL, error);
     }
   }
   
   - (void)URLSession:(NSURLSession *)session
         downloadTask:(NSURLSessionDownloadTask *)downloadTask
         didWriteData:(int64_t)bytesWritten
    totalBytesWritten:(int64_t)totalBytesWritten
   totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite
   {
     // save the total downloaded size
     [self downloaderDidReceiveData:bytesWritten];
     // enable the log only for debugging purpose.
     // LogDebug(@"totalBytesExpectedToWrite %llu, totalBytesWritten %llu, %@", totalBytesExpectedToWrite, totalBytesWritten, downloadTask.currentRequest.URL);
   }
   

3. 如果没有此代码（beginBackgroundTaskWithExpirationHandler），下载会在应用程序被推入后台时停止。

   //  AppDelegate_Phone.m
   - (void)applicationDidEnterBackground: (UIApplication *)application
   {
       NSLog(@"applicationDidEnterBackground");
       UIApplication  *app = [UIApplication sharedApplication];
       UIBackgroundTaskIdentifier bgTask;
   
       bgTask = [app beginBackgroundTaskWithExpirationHandler:^{
           [app endBackgroundTask:bgTask];
       }];
   }
   

Answer 1

您是否在您的应用委托中实现了application:handleEventsForBackgroundURLSession:completionHa‌​ndler:？这应该保存完成处理程序并使用指定的标识符启动后台会话。

如果您不实施该方法，则在应用暂停（或随后在正常应用生命周期过程中终止）后下载是否完成时不会通知您的应用。因此，即使下载完成了，下载也可能看起来没有完成。

（顺便说一句，请注意，如果用户强制退出应用程序，这不仅会终止下载，而且显然不会通知您的应用程序下载已终止，直到用户稍后手动重新启动应用程序并且您的应用会重新实例化后台会话。这是一个次要问题，在主后台处理工作之前您可能不会担心，但需要注意这一点。）

此外，您的 URLSessionDidFinishEventsForBackgroundURLSession: 必须调用已保存的完成处理程序（并将其分派到主队列）。

---

此外，您的设计看起来一次只会发出一个请求。 （我不建议这样做，但我们假设它就像您在上面概述的那样。）因此，让我们假设您已经发出第一个请求，并且应用程序在完成之前被暂停。然后，当下载完成后，应用程序在后台重新启动并调用handleEventsForBackgroundURLSession。假设您已修复该问题以确保它重新启动后台会话，以便可以调用各种委托方法。确保当您发出第二次下载请求时，您使用现有的后台会话，而不是实例化新的。每个标识符只能有一个后台会话。最重要的是，后台会话的实例化应该与downloadWithURL:pathArr:mediaInfo: 分离。只实例化一次后台会话。

Answer 2

在您的 .plist 中添加“必需的背景模式”

在那里，添加“应用从网络下载内容”项