How to raise Notifications from async processes?

[h0lg]

Hey fabulous, I've tried out the new Notifications API in 2.4.0-pre1 and it seems to work fine for synchronous messages, but when trying to notify from an async process, the Dispatcher throws one of these my way:

System.InvalidOperationException
  HResult=0x80131509
  Message=Call from invalid thread
  Source=Avalonia.Base
  StackTrace:
   at Avalonia.Threading.Dispatcher.<VerifyAccess>g__ThrowVerifyAccess|16_0() in Avalonia.Threading\Dispatcher.cs:line 182
   at Avalonia.AvaloniaObject..ctor() in Avalonia\AvaloniaObject.cs:line 96
   at Avalonia.StyledElement..ctor() in Avalonia\StyledElement.cs:line 218
   at Avalonia.Visual..ctor()
   at Avalonia.Layout.Layoutable..ctor()
   at Avalonia.Interactivity.Interactive..ctor()
   at Avalonia.Input.InputElement..ctor() in Avalonia.Input\InputElement.cs:line 507
   at Avalonia.Controls.Control..ctor()
   at Avalonia.Controls.Primitives.TemplatedControl..ctor()
   at Avalonia.Controls.ContentControl..ctor()
   at Avalonia.Controls.Notifications.NotificationCard..ctor()
   at Avalonia.Controls.Notifications.WindowNotificationManager.<Show>d__13.MoveNext()
   at System.Threading.Tasks.Task.<>c.<ThrowAsync>b__128_1(Object state)
   at System.Threading.ThreadPoolWorkQueue.Dispatch()
   at System.Threading.PortableThreadPool.WorkerThread.WorkerThreadStart()

A PR with reproducable examples on the NotificationPage in the Gallery follows.

It also includes some questions regarding the recent changes towards the concept of CmdMsg, which I don't understand, seemingly replacing Cmd<'msg>, which I think I understand by now.

[edgarfgp]

Thanks for raising this issue. This looks like it needs to be run in the UI Thread, in Avalonia you can use

Dispatcher.UIThread.Post(fun _ -> dispatch(NotifyInfo "started"))

Will look like into your PR and add a sample for how to achieve this

[edgarfgp]

Fixed #222

[h0lg]

@edgarfgp Thank you for looking into this :)

I see you created an example for a custom notification position using a model property. I hoped there'd be a less intrusive solution - but I guess that works.

I also find that you refactored my example for multiple dispatched notifications from a background thread into some kind of recursive loop with a timerCmd and some additional messages and helper functions. Apart from making the NotificationPage code quite a bit harder to understand (I can't say I can easily follow that many similar names), it also doesn't answer my question - which was how to use the dispatch function handed to me by Cmd.ofEffect in a less awkward way than Dispatcher.UIThread.Post(fun _ -> dispatch(NotifyInfo "started")).

To be clear, the work - in the examples represented by the Async.Sleep 1000 - should happen on a background thread while the notifications are dispatched on the UI thread as conveniently as possible.

It's up to you whether you want to simplify the NotificationPage examples - but can you tell me how to easily dispatch multiple notifications from Cmd.ofEffect - as in my original example? Thanks!

[h0lg]

how to use the dispatch function handed to me by Cmd.ofEffect in a less awkward way than Dispatcher.UIThread.Post(fun _ -> dispatch(NotifyInfo "started"))

Maybe we have to raise this as an issue in https://github.com/fabulous-dev/Fabulous instead?