ObservableProperty On Changed Not Compiling

[markolbert]

I'm trying to act on changed values of observable properties. This code:

    [ObservableProperty]
    public partial string? Separator { get; set; }
    private partial void OnSeparatorChanged() => _appViewModel.UserConfiguration.Separator = Separator;

generates the following compiler error:

No defining declaration found for implementing declaration of partial method 'FileScanningViewModel.OnSeparatorChanged()'

I thought it might be because the method had to have an argument, but this code:

    [ObservableProperty]
    public partial string? Separator { get; set; }
    public partial void OnSeparatorChanged(string? value) => _appViewModel.UserConfiguration.Separator = value;

generates the following compiler error:

Both partial member declarations must have identical accessibility modifiers.

I'm using VS2026 with all the latest updates installed. What am I doing wrong?

[ghost1372]

Remove private/public word from OnSeparatorChanged

[markolbert]

Sigh... sorry, I figured out what I was doing wrong. Although I don't understand why it was wrong, and would appreciate some education :).

This code (which precisely follows the online documentation) works:

    [ObservableProperty]
    public partial string? Separator { get; set; }
    partial void OnSeparatorChanged(string? value) => _appViewModel.UserConfiguration.Separator = value;

The key difference from one of the things I tried is that there is no scope declaration on the partial method (e.g., public, private).

What I don't understand is I thought declaring the partial method to be public would be okay/required because the related property is explicitly declared as public. I also thought that leaving the scope declaration off -- which is what worked -- would result in the method being considered private, not matching the related property.

Clearly, I don't understand scoping as applied to partial methods... :)