异步任务仍在阻止UI线程

Question

I'm reallt trying to get my head around async/await and Tasks . I'm trying to get one method down so that I can use it throughout my program. Basically I have my own version of BusyIndicator that I want to display whilst work is being done. Here is a basic example;

private async void OnPageLoad(object sender, RoutedEventArgs e)
{
    var waitWindow = new PleaseWaitWindow();

    waitWindow.Show();

    await LoadCompanyContracts();

    waitWindow.Close();
}

private async Task LoadCompanyContracts()
{
    await Task.Run(() =>
    {
        Dispatcher.Invoke(() =>
        {
             //Work done here
        });
    });     
}

Even through these two methods and attempting implementing Tasks my BusyIndicator still doesn't rotate, it is displayed but is frozen so in effect I believe the UI thread is still blocked. How can I modify this piece of code to ensure that all CPU bound work is not blocking the UI thread?

Answer 1

As a general rule, you shouldn't use Dispatcher at all. It's extremely common practice, but it's a commonly bad practice.

private async Task LoadCompanyContracts()
{
  await Task.Run(() =>
  {
    //Work done here
  });
  // Update UI if necessary.
}

Answer 2

Don't do you work inside Dispatcher.Invoke() , because your dispatcher is associated with ui thread. Do your work inside Task and use dispatcher only for updating UI

    private async Task LoadCompanyContracts()
    {
       await Task.Run(() =>
       {
         /*Work done here
          *
          */
         Dispatcher.Invoke(() =>
         {
             //Update UI 
         });
       });     
     }

Answer 3

After looking for some examples in my code here a solution you can try :

    private async void OnPageLoad(object sender, RoutedEventArgs e)
    {
        var waitWindow = new PleaseWaitWindow();

        waitWindow.Show();

        InitLoadCompanyContracts();

        waitWindow.Close();
    }


    private async void InitLoadCompanyContracts(){
        await LoadCompanyContracts();
    }


    private async Task LoadCompanyContracts()
    {
        await Task.Run(() =>
        {
            Dispatcher.Invoke(() =>
            {
                 //Work done here
            });
        });     
    }

I use this to have an awaitable method but out of all "graphics" methods. I don't know if is the best way to do that, but for me it's work.