C＃Windows Phone 8.1运行时：如何使任务在应用程序生命周期之外生存？

Question

I have this kind of Task

    private async Task SaveToFile(StorageFile file)
    {
        // prepare data
        await ...
        Debug.Writeline("completed");
    }

If the user press "back" button this task won't be completed. I need a way to make it go on until all it's done, even if the calling app is not running any more.

Answer 1

No, you can not force a Task to keep running, if the parent process is terminated.

That said, the issue you've described is not really an issue unless your file takes longer than 10 seconds to save (which is an eternity, in computer lingo).

Windows Phone apps continue to run in the background for up to 10 seconds, after the user 'backs' out of it, or manually quits. This should be enough time for any application to finish its 'cleanup' operations.

See: App Lifecycle Windows Runtime Apps

See also: App activation and deactivation for Windows Phone 8

Answer 2

You have To use "background Task" for this. Its pretty simple, create a new project for background tasks and add it to your solution, because your background task is a not a simple class its a separate WINRT project. To do this, right-click on your solution node in the Solution Explorer and select Add->New Project. Then select the Windows Run-time Component (Universal Windows) project type, name the project, and click OK. I named here "BackgroundStuff". You can create more than one background task for single application. there is no any limit. Consider simple example to generate toast even App is not running:

 private async void button_Click(object sender, RoutedEventArgs e) { string myTaskName = "MyBackgroundClass"; // check if task is already registered foreach (var cur in BackgroundTaskRegistration.AllTasks) if (cur.Value.Name == myTaskName) { await (new MessageDialog("Task already registered")).ShowAsync(); return; } // Windows Phone app must call this to use trigger types (see MSDN) await BackgroundExecutionManager.RequestAccessAsync(); // register a new task BackgroundTaskBuilder taskBuilder = new BackgroundTaskBuilder { Name = "MyBackgroundClass", TaskEntryPoint ="MybackgroundStuff.MyBackgroundClass" }; taskBuilder.SetTrigger(new TimeTrigger(15, true)); BackgroundTaskRegistration myFirstTask = taskBuilder.Register(); 

If you want to learn more , refer my blog: http://windowsapplife.blogspot.in/