Visibility modifier for [ObservableProperty] Source Generator

[ewerspej]

I'm currently converting some ViewModels and their properties of a Xamarin.Forms app to use the Source Generators of the MVVM Toolkit.

I've noticed that there is currently no way to modify the visibility of the property setter of a generated property. There are sometimes situations where you would mark a setter as internal, private or protected (or even internal protected), so that a property can only be set by certain actors, while the getter should always be public, so that it can be used in binding expressions.

For example, I would like to be able to use the [ObservableProperty] Source Generator to be able to generate the equivalent of the following:

private string identifier;
public string Identifier
{
    get => identifier;
    private set
    {
        if(identifier.Equals(value)) return;
        identifier = value;
        OnPropertyChanged();
    }
}

The Identifier property could then still be used in a binding expression:

<Label Text="{Binding Identifier}" />

The value can only be set from inside the class, e.g. in a method or command that calls some API:

[RelayCommand]
private async Task UpdateAsync()
{
    Identifier = await RestClient.SomeUpdateCallAsync();
}

This is useful, for example, if the value of the Identifier comes from an API call and shouldn't be publicly settable, or when it should not participate in Two-Way bindings. Therefore there should be a way to modify the visibility.

My proposal is to add an optional visibility modifier to the [ObservableProperty] Source Generator called SetterVisibility which takes a single argument, e.g. an enum value or some other limited form of identifier:

//generates property MyBoolA with private setter
[ObservableProperty(SetterVisibility = Visibility.Private)]
private bool myBoolA;

//generates property MyBoolB with internal setter
[ObservableProperty(SetterVisibility = Visibility.Internal)]
private bool myBoolB;

//generates property MyBoolC with protected setter
[ObservableProperty(SetterVisibility = Visibility.Protected)]
private bool myBoolC;

The resulting properties should then be equivalent to the following:

private bool myBoolA;
public bool MyBoolA
{
    get => myBoolA;
    private set
    {
        if(myBoolA.Equals(value)) return;
        myBoolA = value;
        OnPropertyChanged();
    }
}

private bool myBoolB;
public bool MyBoolB
{
    get => myBoolB;
    internal set
    {
        if(myBoolB.Equals(value)) return;
        myBoolB = value;
        OnPropertyChanged();
    }
}

private bool myBoolC;
public bool MyBoolC
{
    get => myBoolC;
    protected set
    {
        if(myBoolC.Equals(value)) return;
        myBoolC = value;
        OnPropertyChanged();
    }
}

The default must, of course, be Visibility.Public or null in order to not break existing behavior.

This would be highly useful and would allow the MVVM Source Generators to cover more scenarios that already were possible before.

[konstitech]

The feature would be very useful. I miss it

[Sergio0694]

This is included as part of #555. Closing as duplicate of #291.