Application ExitMode

[Gillibald]

• What does the pull request do?
  This PR introduces a way to control when the application exits. You can either let the application exit explicitly or implicitly. Furthermore you can now access the main window and open Windows under the current application instance.
• What is the current behavior?
  The current state calls exit when the main window was closed and there is no way to control this behavior
• What is the updated/expected behavior with this PR?
  You are able to control when the application exits.
• How was the solution implemented (if it's not obvious)?
  In the past all open windows where stored under Window and moved to Application with these changes. A ExitMode property was added to application and a SetExitMode method was added to the AppBuilder.

Checklist:

• Added unit tests (if possible)?
• Added XML documentation to any related classes?
• Consider submitting a PR to https://github.com/AvaloniaUI/Avaloniaui.net with user documentation

See #1565

[grokys]

Thanks for this @Gillibald. This is the same as #1617 right? Next time could you squash your commits and force push instead of creating a new PR? It's best to keep the conversation in one PR. Will review this shortly.

[Gillibald]

Yes it is the same. Just didn't know how to remove the merge commits. This will not happen again in the future. Now i know how to sync my fork properly.

[grokys]

Hmm, now if i set this in ControlCatalog.Desktop:

BuildAvaloniaApp().SetExitMode(ExitMode.OnMainWindowClose).Start<MainWindow>();

The application doesn't appear to start.

Edit: Hmm ignore that, it seems to be working now, not sure what was happening...

[grokys]

Why does this need to be done via an invoke?

[Gillibald]

I haven't found a better solution to show the main window and start up the main loop. The invoke queues the action for execution and gets executed when the main loop runs.

[grokys]

I've tried changing this to:

            mainWindow.Show();
            MainWindow = mainWindow;
            Dispatcher.UIThread.MainLoop(_mainLoopCancellationTokenSource.Token);

And it seems to work. What am I missing?

[Gillibald]

If everything works its fine. Not sure about side effects. My solution only runs after the main loop is running. Maybe show does the same. At some point something has to be invoked on the main thread. Is it possible to call run on a different thread or even Window.Show? My solution would avoid that issue.

[Gillibald]

Just tried what you did and it didn't work. My approach always runs. Don't know why yours work on your environment.

[Gillibald]

Have you tried it with Skia or Direct2D1? Yours works with Skia but not with Direct2D1 on my machine.

[grokys]

I tried it with Win32/D2D but it also works with skia here. Strange that it doesn't work with D2D on your machine, I don't see how the rendering backend would affect whether a window gets shown or not - that should depend on the windowing backend.

It's also strange because this is how it works on master - Window.Show is called from AppBuilderBase.Start before the main loop is started.

[Gillibald]

Dont understand it either has probably something to do with the. net runtime. With .Net Core I dont need invoke. Will remove the invoke call and just hope others don't have the problem.

[grokys]

Could you add some XML documentation to this enum?

[Gillibald]

Will add some comments

[grokys]

Thanks @Gillibald !