How to do not freeze wpf app on closing event

Question

I have a WPF app and I want to execute some method in the Closing event. It can take several minutes, that's why the WPF window freezes. Here is my code:

public MainWindow()
    {
        InitializeComponent();
        this.Closing += MainWindow_Closing;
    }

    void MainWindow_Closing(object sender, System.ComponentModel.CancelEventArgs e)
    {
        Task.Run(new Action(ClaseAfterThreeSecond)).Wait();
    }

    void ClaseAfterThreeSecond()
    {
        Thread.Sleep(3000);
    }

I want to do not freeze the WPF app until MainWindow_Closing ends when I click the X button (close button) on the WPF app. Any suggestions?

EDIT: This way closes the window immediately. I don't need this:

  async void MainWindow_Closing(object sender, System.ComponentModel.CancelEventArgs e)
    {
        await Task.Run(new Action(ClaseAfterThreeSecond));
    }

Answer 1

You need to make your handler async , but as it async void it returns right after your first await call. Just cancel original closing event and close directly in your code:

private async void Window_Closing(object sender, CancelEventArgs e)
{
    // cancel original closing event
    e.Cancel = true;

    await CloseAfterThreeSeconds();
}

private async Task CloseAfterThreeSeconds()
{
    // long-running stuff...
    await Task.Delay(3000);

    // shutdown application directly
    Application.Current.Shutdown();
}