使用NSURLSessionUploadTask在后台上传文件

我正在使用NSURLSessionUploadTask上传多个文件。 我想在后台运行相同的过程，它适用于当前文件。 在当前文件成功上传之前，应用程序不会暂停。 现在，当第二个文件上传时，它不会开始上传过程，直到我再次启动或应用程序变为活动状态。 上传不是介于两者之间。 有没有办法在第一次完成时开始下一个上传过程。 第二次上传也是从后台开始的，但距离应用程序最多可以在3分钟内完成。 这里我展示了我的代码：

AppDelegate.h @property (nonatomic, copy) void(^backgroundTransferCompletionHandler)(); AppDelegate.m - (void)applicationDidEnterBackground:(UIApplication *)application{ __block UIBackgroundTaskIdentifier backgroundTaskIdentifier = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{ NSLog(@"Background Time:%f",[[UIApplication sharedApplication] backgroundTimeRemaining]); [[UIApplication sharedApplication] endBackgroundTask:backgroundTaskIdentifier]; backgroundTaskIdentifier = backgroundTaskIdentifier; `enter code here`}]; } -(void)application:(UIApplication *)application handleEventsForBackgroundURLSession:(NSString *)identifier completionHandler:(void (^)())completionHandler{ self.backgroundTransferCompletionHandler = completionHandler; NSLog(@"handleEventsForBackgroundURLSession called"); } - (void)URLSessionDidFinishEventsForBackgroundURLSession:(NSURLSession *)session{ AppDelegate *appDelegate2 = (AppDelegate *)[[UIApplication sharedApplication] delegate]; NSLog(@"URLSessionDidFinishEventsForBackgroundURLSession call in app delegate"); [session getTasksWithCompletionHandler:^(NSArray *dataTasks, NSArray *uploadTasks, NSArray *downloadTasks) { NSLog(@"uploadTasks: %@",uploadTasks); if ([uploadTasks count] == 0) { if (appDelegate2.backgroundTransferCompletionHandler != nil) { // Copy locally the completion handler. void(^completionHandler)() = appDelegate2.backgroundTransferCompletionHandler; // Make nil the backgroundTransferCompletionHandler. appDelegate2.backgroundTransferCompletionHandler = nil; [[NSOperationQueue mainQueue] addOperationWithBlock:^{ // Call the completion handler to tell the system that there are no other background transfers. completionHandler(); NSLog(@"All tasks are finished"); }]; } } else{ } }]; } UploadView.m - (NSURLSession *)backgroundSession { static NSURLSession *session = nil; static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ NSInteger randomNumber = arc4random() % 1000000; // NSURLSessionConfiguration *sessionConfiguration = [NSURLSessionConfiguration backgroundSessionConfigurationWithIdentifier:[NSString stringWithFormat:@"com.example.apple-samplecode.SimpleBackgroundTransfer.BackgroundSession%d",(int)randomNumber]]; NSURLSessionConfiguration *sessionConfiguration = [NSURLSessionConfiguration backgroundSessionConfigurationWithIdentifier:[NSString stringWithFormat:@"com.upload.myapp.BackgroundSession%d",(int)randomNumber]]; sessionConfiguration.sessionSendsLaunchEvents = YES; sessionConfiguration.HTTPMaximumConnectionsPerHost = 1; // Define the Upload task [sessionConfiguration setHTTPAdditionalHeaders: @{@"Accept": @"text/html"}]; sessionConfiguration.timeoutIntervalForRequest = 600.0; // sessionConfiguration.networkServiceType = NSURLNetworkServiceTypeBackground; // sessionConfiguration.discretionary = YES; sessionConfiguration.allowsCellularAccess = YES; session = [NSURLSession sessionWithConfiguration:sessionConfiguration delegate:self delegateQueue:[NSOperationQueue mainQueue]]; }); return session; } ViewDidLoad(){ .... self.uploadSession = [self backgroundSession]; ....} -UploadStart(){//here i am calling this function in loop. When first file got uploaded, control comes here for second task and then upload should continue. self.uploadTask = [self.uploadSession uploadTaskWithRequest:requestUpload fromFile:[NSURL fileURLWithPath:tmpfile]]; // self.uploadTask is an object of NSURLSessionUploadTask } - (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didSendBodyData:(int64_t)bytesSent totalBytesSent:(int64_t)totalBytesSent totalBytesExpectedToSend:(int64_t)totalBytesExpectedToSend { } - (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveData:(NSData *)data { NSLog(@"didReceiveData Task: %@ upload complete", dataTask); NSHTTPURLResponse *httpResp = (NSHTTPURLResponse*) self.uploadTask.response; if (httpResp.statusCode == 200) { uploadedFiles++; //an int value if(uploadedFiles==arrUpload.count){ //all files uploaded here } else{ //upload next file from here } } } - (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error { } - (void)URLSessionDidFinishEventsForBackgroundURLSession:(NSURLSession *)session{ NSLog(@"URLSessionDidFinishEventsForBackgroundURLSession called"); AppDelegate *appDelegate2 = (AppDelegate *)[[UIApplication sharedApplication] delegate]; if (appDelegate2.backgroundTransferCompletionHandler != nil) { // Copy locally the completion handler. void(^completionHandler)() = appDelegate2.backgroundTransferCompletionHandler; // Make nil the backgroundTransferCompletionHandler. appDelegate2.backgroundTransferCompletionHandler = nil; [[NSOperationQueue mainQueue] addOperationWithBlock:^{ // Call the completion handler to tell the system that there are no other background transfers. completionHandler(); NSLog(@"All tasks are finished"); }]; } } 

以上代码完全正常工作，但是在App后台模式3分钟后，下一个文件的问题没有开始在后台上传。

任何帮助将不胜感激。 在此先感谢…如需更多解释，请与我联系。