问Metro App Detect Printer Charm打开和关闭

EN

<Grid Background="{StaticResource ApplicationPageBackgroundThemeBrush}">
    <Button Click="Button_Click_1" Content="Print" />
</Grid>

public sealed partial class BlankPage2 : Page
{
    public BlankPage2()
    {
        this.InitializeComponent();
        PrintManager printMan = PrintManager.GetForCurrentView();
        printMan.PrintTaskRequested += PrintTaskRequested;
    }

    private void PrintTaskRequested(PrintManager sender, PrintTaskRequestedEventArgs e)
    {
        System.Diagnostics.Debug.WriteLine("Printer Opened");
        //TODO:
        PrintTask printTask = e.Request.CreatePrintTask(....);
        printTask.Completed += printTask_Completed;
    }

    void printTask_Completed(PrintTask sender, PrintTaskCompletedEventArgs args)
    {
        //TODO:
    }


    private async void Button_Click_1(object sender, RoutedEventArgs e)
    {
        await Windows.Graphics.Printing.PrintManager.ShowPrintUIAsync();
    }
}