x:Bind subscriptions should not linger after their target is unloaded

[jeromelaban]

Current behavior

x:Bind subscriptions are still raising property changes for unloaded controls

Expected behavior

Properties are not updated

How to reproduce it (as minimally and precisely as possible)

No response

Workaround

No response

Works on UWP/WinUI

None

Environment

No response

NuGet package version(s)

5.1.104

Affected platforms

No response

IDE

No response

IDE version

No response

Relevant plugins

No response

Anything else we need to know?

No response

[Youssef1313]

In WinUI, I see that the binding is still working, even after the control is unloaded.

XAML:

<Page x:Class="UnoApp14.MainPage"
      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
      xmlns:local="using:UnoApp14"
      Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
  <StackPanel Margin="5" x:Name="sp">
    <TextBlock Text="{x:Bind VM.Value, Mode=TwoWay}" x:Name="myTb" />
    <Button Click="Button_Click">Click me</Button>
    <TextBlock Text="Logs:" x:Name="logTB" />
  </StackPanel>
</Page>

Code-behind:

//#define PUSH_FROM_VM_TO_CONTROL

using System.ComponentModel;

namespace UnoApp14;

public sealed partial class MainPage : Page
{
    private int counter;

    public MainPage()
    {
        this.InitializeComponent();
        VM = new VM(Log);

        myTb.Unloaded += myTb_Unloaded;
        myTb.RegisterPropertyChangedCallback(TextBlock.TextProperty, OnTextChanged);
    }

    private void Log(string text)
        => logTB.Text += "\r\n" + text;

    private void myTb_Unloaded(object sender, RoutedEventArgs e)
    {
        Log("TextBlock unloaded.");
    }

    private void OnTextChanged(DependencyObject sender, DependencyProperty dp)
    {
        Log("Text changed.");
    }

    public VM VM { get; }

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        Log("\r\nButton clicked");

#if PUSH_FROM_VM_TO_CONTROL
        VM.Value = (counter++).ToString();
#else
        myTb.Text = (counter++).ToString();
#endif

        if (counter == 5)
        {
            Log("Removing TextBlock.");
            sp.Children.Remove(myTb);
        }
    }
}

public class VM : INotifyPropertyChanged
{
    private readonly Action<string> _log;

    public VM(Action<string> log)
        => _log = log;

    public event PropertyChangedEventHandler? PropertyChanged;

    private string? _value;

    public string? Value
    {
        get => _value;
        set
        {
            _log($"VM.set_Value is called with: {value}");
            if (_value != value)
            {
                _value = value;
                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Value)));
            }
        }
    }
}

The outcome on WinUI:

And on Uno WPF:

---

With PUSH_FROM_VM_TO_CONTROL:

WinUI:

Uno WPF:

For this case, there is an unimportant behavior mismatch that the setter is called twice on WinUI but once with Uno. But that shouldn't be a problem as usually the property will do nothing if its backing field is the same as the coming value (otherwise it should stackoverflow in WinUI anyways)

---

So, with the above repro, I can't see that subscriptions should die after unloading.

UnoApp14.zip

[jeromelaban]

Related pr: #16631