CommandAsyncChecked does not respect CanExecute's return value about fsharp.viewmodule

[FoggyFinder]

A similar question has already been asked on SO:

http://stackoverflow.com/questions/35554054/f-wpf-async-command-completion-status/35558857

Thus:

    [<STAThread; EntryPoint>]
    let main argv = 
        if SynchronizationContext.Current = null then
            DispatcherSynchronizationContext(Dispatcher.CurrentDispatcher)
            |> SynchronizationContext.SetSynchronizationContext
        let win = MainWindow()
        win.Root.DataContext <- MainWindowViewModel()
        let app = Application()
        app.Run(win.Root)

[WallaceKelly]

@FoggyFinder Thank you for the SO link. I had not found that.

I added the code to SetSynchronizationContext to my demo. It is an improvement. The button becomes re-enabled when the asyncWorkflow completes. However, I want to do some more research. The behavior is still not exactly what I would have expected. (I would not have expected the button to be disabled while the asyncWorkflow runs.) But, my expectations may be the problem. Thanks again!

[ReedCopsey]

@WallaceKelly we don't always disable, because there are times when people want to allow more than one execution.

If you make can execute return not self.OperationExecuting it'll disable and re-enable automatically

[WallaceKelly]

@ReedCopsey I'm glad to hear how you describe it, because that is what I expected. However, that is not what I'm seeing. The behavior I'm seeing is that the button becomes disabled, only allowing one execution, even if my canExecute always returns true.

[ReedCopsey]

@WallaceKelly I'm not sure I follow - you definitely need @FoggyFinder 's workaround (the Sync Context setup I posted in SO). That's actually an issue in C# if you build your own app, too, and use async/await heavily in the VM.

Once that's there, if you change your CanExecute as I mentioned, it should enable/disable:

let canExecute _ = not self.OperationExecuting
member val DoSomethingAsync =
        this.Factory.CommandAsyncChecked(asyncWorkflow, canExecute, [ <@ this.OperationExecuting @> ])

This sample from FsXaml shows some ideas around using operation executing: https://github.com/fsprojects/FsXaml/blob/master/demos/WpfMvvmAgent/MainViewModel.fs

If it's still not working, can you post a full repro? I'll take a look.

[FoggyFinder]

(I would not have expected the button to be disabled while the asyncWorkflow runs.)

@WallaceKelly, You mean something like this?

    let asyncWorkflowS() =
        async {
            do! Async.Sleep(3000)
            System.Diagnostics.Debug.WriteLine("asyncWorkflow completed.")
        } |> Async.Start

    member val DoSomethingAsync =
        this.Factory.CommandSyncChecked(asyncWorkflowS, canExecute)