Add examples for Notifications from async operations

[h0lg]

Provides reproducable examples for the exceptions mentioned in #221 on the NotificationPage in the Gallery.

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 this PR. I will go through it during the week and make some notes where we can add more docs or samples.

[edgarfgp]

Bear in mind that all of this is a port for the Avalonia Catalog samples, so I just wanted to test in the control works for us. have not really put too much though on making this side-effect free per se. Just adding some samples

[h0lg]

I see. This was just something where the behaviour surprised me. Not so much after seeing the assignment NotificationManager = FabApplication.Current.WindowNotificationManager in the source - but it still raised the question of how I'd customize the position of just one message without doing the same for all following messages. Would I have to remember the original Position and reset it after model.NotificationManager.Show?

[edgarfgp]

So to control the position of a single Notification you can use:

let controlNotificationsRef = ViewRef<WindowNotificationManager>()

let update msg model =
    match msg with
    | ControlNotificationsShow ->
            // You can put in a Cmd If you want
            controlNotificationsRef.Value.Show(Notification("Control Notifications", "This notification is shown by the control itself."))
            model, []

// We can use the WindowNotificationManager a widget to be able to have a different WindowNotificationManager than FabApplication.Current.WindowNotificationManager
 // Allowing you control ie the Position of a single notification
WindowNotificationManager(controlNotificationsRef)
     .position(model.NotificationPosition)
     .dock(Dock.Top)
     .maxItems(3)

[h0lg]

@edgarfgp Thank you for taking the time to respond :) Your suggestion worked for one of the added scenarios examples. I have converted your feedback into hopefully helpful comments and updated my questions for you to have a look at when you get to it.

[edgarfgp]

Just had a second look at this. We can use the Dispatcher.UIThread.Post here

Dispatcher.UIThread.Post(fun _ -> 
    model.NotificationManager.Show(Notification(message, "", NotificationType.Information)
)

and remove it from the the notifyAsyncStatusUpdates and notifyOneAsync and will fix cover both use cases

Edit: It is not recommended to access UI-related stuff from either init or update for that exact same reason
The correct approach is to push back the access to those UI stuff in Cmd, and then make sure those Cmd run on the UI thread if required. See my last commit

[edgarfgp]

Ok so finally had some time to check this sample and made some improvements based on your question in this PR

[edgarfgp]

So to control the position of a single Notification you can use:

let controlNotificationsRef = ViewRef<WindowNotificationManager>()

let update msg model =
    match msg with
    | ControlNotificationsShow ->
            // You can put in a Cmd If you want
            controlNotificationsRef.Value.Show(Notification("Control Notifications", "This notification is shown by the control itself."))
            model, []

// We can use the WindowNotificationManager a widget to be able to have a different WindowNotificationManager than FabApplication.Current.WindowNotificationManager
 // Allowing you control ie the Position of a single notification
WindowNotificationManager(controlNotificationsRef)
     .position(model.NotificationPosition)
     .dock(Dock.Top)
     .maxItems(3)

[edgarfgp]

Thanks for this PR. Improved the sample and took some notes to write some docs to clarify the CmdMsg and the new Program functions.