ReactiveCommand gives System.InvalidOperationException after binding

[goyzhang]

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Do you want to request a feature or report a bug?

Bug

What is the current behavior?

After binding the command to , for instance, a button. Click the button will cause System.InvalidOperationException indicating that object owns by another thread right after the callback returns.

If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem

in xaml:
<Button Command="{Binding MyCommand}"></Button>

in viewmodel:

public ReactiveCommand MyCommand { get; protected set; }
        public MainWindowViewModel()
        {
            MyCommand =ReactiveCommand.CreateFromTask(() =>
            {
                Console.WriteLine("foo"); //this works
                return Task.Run(() => {

                });
            });//cause exception right after return
        }

What is the expected behavior?

Works as any command. No exception.

What is the motivation / use case for changing the behavior?

Which versions of ReactiveUI, and which platform / OS are affected by this issue? Did this work in previous versions of ReativeUI? Please also test with the latest stable and development snapshot
In v8.3.1 with reactive 3.3.1 & .net 4.7.1 WPF project
Same codes work fine in v7.4

Other information (e.g. stacktraces, related issues, suggestions how to fix)

[phenomx2]

Why are you using Task.Run(...) why not use await ?

[goyzhang]

@phenomx2 That makes no different. I just want to give it a quick demo and the API does not require that to be async/await pattern.

[phenomx2]

Can you share a small repo with the bug ? please

[goyzhang]

check this repo

[Fido789]

I can confirm this bug. Even empty command ReactiveCommand.Create(()=>{}) throws the exception.

[Qonstrukt]

ReactiveCommand without generic parameters should never be used. It's still there because of compatibility with ICommand. But when you define your property like this:

public ReactiveCommand<Unit, Unit> MyCommand { get; set;}

You'll see that it works. It's not clear at all though, and the docs use the wrong (old) syntax still sometimes. Everything always seems to work, until you start binding.

[glennawatson]

We probably should add a issue on the website project to upload the instances where this is wrong in the documentation I guess.

[goyzhang]

umm.In v7.4 it works fine though. Is it possible to make this to be a synax error so that it won't even pass the compiler? Or by default it accept a task class as the generic parameter.

[glennawatson]

Potentially, will investigate and see if I can make the change. Obviously will be breaking but will likely stop fairly subtle bugs like this one.

[gabbacode]

for everyone who stepped on this rake:
just install ReactiveUI.WPF NuGet package

have found solution on so ;)
https://stackoverflow.com/questions/51747323/how-to-use-reactivecommand

Stack Overflow

How to use ReactiveCommand?

I have a viewmodel that uses ReactiveCommand:

public ReactiveCommand<Unit, Unit> Command { get; }

public MyViewModel()
{
Command = ReactiveCommand<Unit, Unit>.Create(MyMethod);
}
...

[worldbeater]

This happens because ReactiveUI schedulers won't get properly initialized when one uses a XAML UI framework and doesn't have a platform-specific package installed. ReactiveUI main package should normally be installed into your .NET Standard or UWP assembly only. For other platforms use one of these packages: ReactiveUI.WPF, ReactiveUI.XamForms, ReactiveUI.WinForms or Avalonia.ReactiveUI. See Installation/NuGet-Packages for more info.

If you install the packages correctly, but still get the exception thrown, make sure you are accessing the UI from a proper thread. Adding a call to .ObserveOn(RxApp.MainThreadScheduler) where necessary should do the trick. See ObserveOn docs.

[glennawatson]

Reopening since using this as a tracker to remove the abstract ReactiveCommand class.