[BUG] [ObservableProperty] OnChanged Callback Not Firing with TwoWay Binding

[SuthiYuvaraj]

Describe the bug

When using [ObservableProperty] from CommunityToolkit.Mvvm 8.4 on a bool property bound TwoWay to Microsoft.Maui.Controls.Picker.IsOpen, the generated OnIsProjectPickerExpandedChanged method is never called

Regression

8.0.3

Steps to reproduce

• Run the ObservablePropertyIssue sample attached in this https://github.com/SuthiYuvaraj/Samples/tree/main/ObservablePropertyIssue repository.
• Open the Picker and select an item.
• After selecting the item, the SelectionText is not updated. The PropertyChanged notification is never raised.

<Picker Title="Select a project" 
        ItemsSource="{Binding Projects}" 
        ItemDisplayBinding="{Binding Name, x:DataType=models:Project}" 
        SelectedItem="{Binding SelectedProject}" 
        SelectedIndex="{Binding SelectedProjectIndex}" 
        IsOpen="{Binding IsProjectPickerExpanded, Mode=TwoWay}"/>

public partial class MainPageViewModel : ObservableObject
{
    [ObservableProperty]
    private bool _isProjectPickerExpanded;

    [ObservableProperty]
    private string _selectionText = "No project selected";

    partial void OnIsProjectPickerExpandedChanged(bool value)
    {
        SelectionText = value
            ? "Picker is open..."
            : SelectedProject is not null
                ? $"Selected: {SelectedProject.Name} – {SelectedProject.Description}"
                : "No project selected";
    }

    // ...
}

With reference to the code snippet , OnIsProjectPickerExpandedChanged is never called.

Expected behavior

The OnIsProjectPickerExpandedChanged PropertyChanged method is expected to be invoked whenever the IsOpen property changes.

Screenshots

No response

IDE and version

VS 2022

IDE version

No response

Nuget packages

• CommunityToolkit.Common
• CommunityToolkit.Diagnostics
• CommunityToolkit.HighPerformance
• CommunityToolkit.Mvvm (aka MVVM Toolkit)

Nuget package version(s)

8.0.4

Additional context

• .NET MAUI CommunityToolkit:8.0.4
• OS: MacCatalyst Xcode 26.2
• .NET MAUI:11.0.0-preview.1.26104.11

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[Sergio0694]

I'm not seeing anything in that repro that might explain how this might be related to the MVVM Toolkit.

• Can you repro the issue if you replace that with a manually implemented observable property?
• Can you repro the issue if you use a partial property instead of a field? (maybe MAUI has some generators ignoring fields?)

[SuthiYuvaraj]

Hi @Sergio0694 ,

• The issue does not reproduce when using a manually implemented INotifyPropertyChanged; the CommandParameter works as expected in this case.
• The issue does reproduce when using [ObservableProperty] from the MVVM Toolkit, regardless of whether it is backed by a field or a partial property.
• This behaviour worked correctly in .NET 10 with CommunityToolkit 8.0.3 and regressed in .NET 11.
• A reproduction repository has been provided to help demonstrate the issue.
  Repo link https://github.com/SuthiYuvaraj/Samples/tree/main/ObservablePropertyIssue