Problems with MVVM Toolkit

[RedX2501]

Fody: 6.5.1
PropertyChanged.Fody: 3.4.0

Describe the issue

The following code

    [ObservableObject]
    public partial class AnyViewModel
    {
        [ObservableProperty]
        private string someField = "hey";
    }

Generates the following code:

[GeneratedCode("Microsoft.Toolkit.Mvvm.SourceGenerators.ObservablePropertyGenerator", "7.1.0.0")]
[DebuggerNonUserCode]
[ExcludeFromCodeCoverage]
public string SomeField
{
	get
	{
		return someField;
	}
	set
	{
		if (!EqualityComparer<string>.Default.Equals(someField, value))
		{
			OnPropertyChanging(__KnownINotifyPropertyChangedOrChangingArgs.SomeFieldPropertyChangingEventArgs);
			someField = value;
			OnPropertyChanged(<>PropertyChangedEventArgs.SomeField);
			OnPropertyChanged(__KnownINotifyPropertyChangedOrChangingArgs.SomeFieldPropertyChangedEventArgs);
		}
	}
}

1. Any assignment of different values to someField will generate a duplicate PropertyChanged event.

Settings [PropertyChanged.DoNotNotify] on the field has no effects (obviously).

Minimal Repro

1. Copy paste the example above in any WPF project using Microsoft.MVVM.Toolkit.
2. Compile.
3. Look at the IL.

Make an effort to fix the bug

Maybe the generator should see that a (oddly) placed call to the OnPropertyChanged already exists and therefore not emit one?

Or should [PropertyChanged.DoNotNotify] be extended to also work on fields? For some reason the flags already indicate that it can be set on fields but it has no effect.

[tom-englert]

Looks you are mixing two incompatible frameworks. If you are using [ObservableProperty], don't use Fody.PropertyChanged.
Both are trying to do the same thing, but don't know about each other.

Why would you need both Fody.PropertyChanged and MVVM in the same project?

[RedX2501]

Because MVVM Toolkit does not automatically do the PropertyChanged call for properties. Only for fields and only when you annotate them with ObservableProperty.

Then should maybe the DoNotNotify attribute have it's AttributeTargets.Field flag removed to avoid confusion? What feature of PropertyChanged.Fody is used on fields that could use this flag?

[ltrzesniewski]

Then should maybe the DoNotNotify attribute have it's AttributeTargets.Field flag removed to avoid confusion? What feature of PropertyChanged.Fody is used on fields that could use this flag?

Yup, it's inconsistent. I opened #847 to fix this.

[tom-englert]

Deployed.