Stream binding operator does not work in two way mode for TextBox, NumericUpDown

[legezam]

Describe the bug

I might be misunderstanding how it is supposed to work, but when i bind the Text property of Text or Value property of NumericUpDown in two way mode to a Subject, using stream binding operator, i get no updates in the viewmodel when changing the state of the control on the ui. Please see the attached example.

However, it works very well for ScrollView.Offset property.

am i getting something wrong?

To Reproduce

Could be reproduced easily in the avalonia starter template.

Mainwindow.xaml:

<Window xmlns="https://github.com/avaloniaui"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:vm="using:AvaloniaApplication1.ViewModels"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
        x:Class="AvaloniaApplication1.Views.MainWindow"
        x:DataType="vm:MainWindowViewModel"
        Icon="/Assets/avalonia-logo.ico"
        Title="AvaloniaApplication1">

    <TextBox Text="{Binding Foo^, Mode=TwoWay}"></TextBox>

</Window>

MainwindowViewModel.cs:

using System;
using System.Reactive.Subjects;
using ReactiveUI;
using Console = System.Console;
using System.Reactive.Linq;
using System.Reactive;

namespace AvaloniaApplication1.ViewModels;

public partial class MainWindowViewModel : ReactiveObject
{
    private BehaviorSubject<string> foo = new("hello");

    public BehaviorSubject<string> Foo => foo;

    public MainWindowViewModel()
    {
        foo.Subscribe(x => Console.WriteLine(x));
    }
}

Everything else is left unchanged in the starter template.

I have only added ReactiveUI - 20.1.63 package.

I see "hello" appear in th econtrol but then I expect values printed to the console when i change the value of the TextBox on the ui.

Thanks!

Expected behavior

Just as if i have bound the Offset property of a ScrollViewer, and listened for updates, i get console messages printed upon change.

Avalonia version

11.2.1

OS

Linux

Additional context

No response

[maxkatz6]

I don't think stream operator ever supported two-way bindings (i.e. assuming it should write back to IObserver/Subject).
Implementation also only refers to one-way listening: https://github.com/AvaloniaUI/Avalonia/blob/master/src/Avalonia.Base/Data/Core/Plugins/IStreamPlugin.cs#L8

[legezam]

Thanks for checking, tha explains a lot! But then the question arises, how Scrollviewer.Offset writeback works?