Control over Avalonia Message Loop

[kuiperzone]

It would be complex to explain fully what I'm trying to do here, but I need to chain together custom blocking functions called in response to events, while preserving the MainWindow and responding to Avalonia events.

Essentially, I need to enter the Avalonia message loop, come out of it on demand, and then go back in.

To phrase it another way, I need the equivalent of a Window.ShowDialog() method on a Window that is already visible.

I'm reading:
https://docs.avaloniaui.net/docs/concepts/application-lifetimes

I see the code:

  // Application entry point. Avalonia is completely initialized.
  static void AppMain(Application app, string[] args)
  {
     // A cancellation token source that will be 
     // used to stop the main loop
     var cts = new CancellationTokenSource();
     
     // Do your startup code here
     new Window().Show();

     // Start the main loop
     app.Run(cts.Token);
  }

Q. What I'm asking is can I cancel Run(), end then re-enter it? Something like...

 new Window().Show();

 var cts1 = new CancellationTokenSource();
 app.Run(cts1.Token);

 // Cancelled, but re-enter
 var cts2 = new CancellationTokenSource();
 app.Run(cts2.Token);

Would this work?

Is the another way to do it?

[maxkatz6]

You need a DispatcherFrame API, which is more or less the same in Avalonia like on WPF.
Keep in mind it will only work on Desktop where we have full control over app loop. We don't have that on mobile or browser (normally).

[kuiperzone]

Just want to thank you for your reply. I may follow this up when I have discovered a path to go down for my solution.

[kuiperzone]

I'm not up to speed on WASM yet, but would need to my solution to eventually work in a browser.

I'm thinking that the way to go might be to employ 2 long running threads. One is the app main which can handle Avalonia. The other I will use to handle the blocking calls as mentioned above. The only thing needed would be a way to get the two to communicate.

Q. I'm a little confused by threads in WASM. In some literature, I read that they are not implemented in .NET 8 but might be .NET 9.

On the other hand, I see you guys already using them:

#14022

Any problems in WASM using the Thread class or Task?

[maxkatz6]

.NET 8 WASM supports threads (including Thread class), but .NET 9 has it completely refactored and redone on runtime level.
In case of Avalonia, we supported .NET 8 WASM threads, but we are going to only support .NET 9.

Specifically about combination of Avalonia 11.2 and .NET 9 WASM threading, DispatcherFrame API will work there.

[kuiperzone]

Thank you @maxkatz6