Add support for combining NotifyParentPropertyAttribute and ObservablePropertyAttribute

[stcmz]

Overview

System.ComponentModel.NotifyParentPropertyAttribute can only decorate a property but a ObservableProperty must be defined as a field so that a property can be generated automatically.

To allow them to work together, we should either provide a CommunityToolkit implementation of NotifyParentPropertyAttribute or allow ObservablePropertyAttribute to be used with a partial property (#555).

For now, the latter is infeasible as C# does not allow partial properties.

API breakdown

namespace CommunityToolkit.Mvvm.ComponentModel;

[AttributeUsage(AttributeTargets.Field, AllowMultiple = false, Inherited = false)]
public sealed class NotifyParentPropertyAttribute : Attribute
{
    public NotifyParentPropertyAttribute(bool notifyParent)
    {
        NotifyParent = notifyParent;
    }

    public bool NotifyParent { get; }
}

Usage example

public partial class ChildModel : ObservableObject
{
    [ObservableProperty]
    [NotifyParentChanged(true)]
    private string _name;
}

public partial class ParentModel : ObservableObject
{
    [ObservableProperty]
    private ChildModel _child = new ();
}

When the Child.Name property gets updated, the ParentModel should be notified for the change of the Child property, i.e., OnPropertyChanged(nameof(Child)) should be called.

var parentModel = new ParentModel();
parentModel.Child.Name = "something"; // should call OnPropertyChanged(nameof(Child))

Breaking change?

No

Alternatives

Currently one has to choose between [NotifyParentChanged(true)] and [ObservableProperty].

Additional context

No response

Help us help you

Yes, but only if others can assist