[Bug]: ReactiveCommand doesn't propagate output on WinForms

[Micha-kun]

Describe the bug 🐞

I'm developing a .NET 10 WinForms app using ReactiveUI 23.1.8 and ReactiveUI.SourceGenerators 2.6.1. I'm trying to use the output of a ReactiveCommand so I can invoke another commands or binding to property, but I'm getting no response in any way.

Step to reproduce

I have this viewmodel. There are comments where problems arise.

public ShellViewModel(ISchedulerProvider schedulerProvider)
{
    this.Router = new(schedulerProvider.MainThread);
    this.schedulerProvider = schedulerProvider;
    this.WhenActivated(
        d =>
        {
            _ = this.WhenAnyObservable(vm => vm.NavigateToCommand).Subscribe(x => { }).DisposeWith(d); // Does nothing
            _ = this.NavigateToCommand.IsExecuting.Subscribe(_ => { }).DisposeWith(d); // Only generates the first false value
            _ = this.NavigateToCommand.Subscribe(x => { }).DisposeWith(d); // Does nothing
            _ = Observable.Return(ShellPages.Clients).InvokeCommand(this, vm => vm.NavigateToCommand).DisposeWith(d); // This executes as expected
            // _ = this.NavigateToCommand.Execute(ShellPages.Clients).Subscribe().DisposeWith(d); // I tried that too, executes as expected, propagates nothing.
        });
}

[ReactiveCommand]
private IObservable<IRoutableViewModel?> NavigateTo(ShellPages shellPage)
{
    return Observable.Create<IRoutableViewModel?>(observer =>
    {
        var result = ... // Get new routable viewmodel
        observer.OnNext(result);
        Thread.Sleep(TimeSpan.FromSeconds(5)); // This is forced for testing, to see if IsExecuting would rise. It doesn't change anything if it exists or not.
        observer.OnCompleted();
        return Disposable.Empty;
    }).WhereNotNull().SelectMany(this.Router.NavigateAndReset.Execute);
}

Command executes completelly, even the NavigateAndReset command one, and Router.CurrentViewModel observable responds as expected.

Firstly I tried to make that navigation thing as response from the output of the command, but because didn't work, I put inside command, but I don't like that, I prefer to use ReactiveCommand as an output propagator.

Reproduction repository

https://github.com/reactiveui/ReactiveUI

Expected behavior

ReactiveCommand output should be propagated.

Screenshots 🖼️

No response

IDE

Visual Studio 2026

Operating system

Windows 11

Version

No response

Device

No response

ReactiveUI Version

23.1.8

Additional information ℹ️

No response

[Micha-kun]

I'm testing the simplest code using "pure rxui" and I still got nothing:

var command = ReactiveCommand.Create(() => 1);
command.Subscribe(x => { }).DisposeWith(d); // Nothing
command.Execute().Subscribe().DisposeWith(d);

[glennawatson]

Going to get @ChrisPulman to have a look. Debatable if it's rxui or the rxui generators.

[Micha-kun]

Thank you @glennawatson . The second test (the simplest one) is using "pure rxui", so I think is something internal. Maybe is related to the new RxAppBuilder. Because I'm using Host.CreateApplicationBuilder for my app configuration, I'm executing only this code for enabling rxui:

RxAppBuilder.CreateReactiveUIBuilder()
                    .WithWinForms()
                    .BuildApp();

Without it, WhenActivated throws an error (even when View implements IViewFor):

Don't know how to detect when ShellView is activated/deactivated, you may need to implement IActivationForViewFetcher

And using this:

RxAppBuilder.CreateReactiveUIBuilder()
                    .WithWinForms()
                    .Build();

Makes my app simply crash without any error or anything. It simply closes.