Objective c Swift-Copy completionHandler
我一直在遵循Appcoda的教程: 但是用swift写。我遇到了这一行代码,我无法在swift中工作Objective c Swift-Copy completionHandler,objective-c,swift,background,appdelegate,completionhandler,Objective C,Swift,Background,Appdelegate,Completionhandler,我一直在遵循Appcoda的教程: 但是用swift写。我遇到了这一行代码,我无法在swift中工作 -(void)URLSessionDidFinishEventsForBackgroundURLSession:(NSURLSession *)session{ AppDelegate *appDelegate = [UIApplication sharedApplication].delegate; // Check if all download tasks have be
-(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];
}];
}
}
}];
}
我不能正确理解的部分是:
void(^completionHandler)() = appDelegate.backgroundTransferCompletionHandler
我有appDelegate.backgroundTransferCompletionHandler变量,但我不知道如何将其分配给void(^completionHandler)()。
swift无法识别void(^completionHandler)()
这方面的帮助将不胜感激。您可能应该处理应用程序委托,因为这就是
completionHandler
闭包的定义所在。您可能会将backgroundTransferCompletionHandler
属性定义为一个闭包,该闭包是可选的,可能类似于:
var backgroundTransferCompletionHandler: (() -> ())?
func application(application: UIApplication, handleEventsForBackgroundURLSession identifier: String, completionHandler: () -> Void) {
backgroundTransferCompletionHandler = completionHandler
// do whatever else you want (e.g. reinstantiate background session, etc.)
}
然后,您在问题中引用的代码的Swift格式副本将获取该completionHandler
的本地副本,如下所示:
let appDelegate = UIApplication.sharedApplication().delegate as AppDelegate
let completionHandler = appDelegate.backgroundTransferCompletionHandler
然后称之为:
completionHandler?()
是否应将此void(^completionHandler)()替换为void(^completionHandler)(void),谢谢Rob。完美地工作