Swift - 複製完成處理程序

Question

我一直在關注Appcoda的一個教程：http://www.appcoda.com/background-transfer-service-ios7/ 但是在swift中編寫它。我所遇到的這行代碼，我不能得到迅速

-(void)URLSessionDidFinishEventsForBackgroundURLSession:(NSURLSession *)session{ 
    AppDelegate *appDelegate = [UIApplication sharedApplication].delegate; 

    // Check if all download tasks have been finished. 
    [self.session getTasksWithCompletionHandler:^(NSArray *dataTasks, NSArray *uploadTasks, NSArray *downloadTasks) { 
     if ([downloadTasks count] == 0) { 
      if (appDelegate.backgroundTransferCompletionHandler != nil) { 
       // Copy locally the completion handler. 
       void(^completionHandler)() = appDelegate.backgroundTransferCompletionHandler; 

       // Make nil the backgroundTransferCompletionHandler. 
       appDelegate.backgroundTransferCompletionHandler = nil; 

       [[NSOperationQueue mainQueue] addOperationWithBlock:^{ 
        // Call the completion handler to tell the system that there are no other background transfers. 
        completionHandler(); 

        // Show a local notification when all downloads are over. 
        UILocalNotification *localNotification = [[UILocalNotification alloc] init]; 
        localNotification.alertBody = @"All files have been downloaded!"; 
        [[UIApplication sharedApplication] presentLocalNotificationNow:localNotification]; 
       }]; 
      } 
     } 
    }]; 
} 

我不能得到正確的部分工作是：

void(^completionHandler)() = appDelegate.backgroundTransferCompletionHandler 

我有appDelegate.backgroundTransferCompletionHandler可變的，但我不不知道如何將它分配給void（^ completionHandler）（）。 void（^ completionHandler）（）不被swift識別。

對此的幫助將不勝感激。

Answer 1

您可能應該處理應用程序委託，因爲這是關閉閉包的定義所在。你可能會定義backgroundTransferCompletionHandler屬性爲封閉這是一個可選的，也許是這樣的：

var backgroundTransferCompletionHandler: (() ->())? 

func application(application: UIApplication, handleEventsForBackgroundURLSession identifier: String, completionHandler:() -> Void) { 
    backgroundTransferCompletionHandler = completionHandler 

    // do whatever else you want (e.g. reinstantiate background session, etc.) 
} 

然後，你在你的問題中引用的代碼斯威夫特移交會搶completionHandler的本地副本，像這樣：

let appDelegate = UIApplication.sharedApplication().delegate as AppDelegate 

let completionHandler = appDelegate.backgroundTransferCompletionHandler 

然後調用它：

completionHandler?()