Multiple Inheritance Compiler Error CS1721

[SkyGen]

Describe the bug

Hi!

I would like to use ObservableObject for MVVM projects but I would need to inherit from multiple classes (see error in screenshot). My projects must inherit from DockPane, as it is a required class for the company I work for.

I noticed in the doc for error CS1721, it mentions a class may only inherit directly from a single class; however, a class can implement any number of interfaces. Is there a chance you might add an IObservableObject interface to CommunityToolkit.Mvvm?

Thanks! -Denny

Regression

No response

Steps to reproduce

Allow multiple inheritance via interface. See Expected Behavior example.

Expected behavior

partial class OutputDockPane : DockPane, IObservableObject { }

Screenshots

IDE and version

VS 2022

IDE version

17.5.0

Nuget packages

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

Nuget package version(s)

8.1.0

Additional context

No response

Help us help you

No, just wanted to report this

[TruePluto]

I don't think It is a good idea to make a DockPanel as a ObservableObject because it is a class of view, ObservableObject is used as a ViewModel but if you insist you can try the following code

[ObservableObject]
partial class OutputDockPane : DockPane
{
}

[SkyGen]

Thanks @TruePluto

[Sergio0694]

This is by design. As mentioned, C# doesn't support multiple inheritance. For situations like these though, you can work around it and get the same functionality by using [ObservableObject], that's exactly what it's made for 🙂 My suggestion would be to have a base type like this:

[ObservableObject]
public abstract partial class ObservableDockPane : DockPane
{
}

And then just always inherit from this one for your types. This will give you the same features but it will greatly reduce binary size compared to just always using [ObservableObject] in each of your types (as this way the code will be shared).

[SkyGen]

Much thanks, @Sergio0694. Unfortunatley I can't use the attribute decoration either because one of the DockPane base classes implements INotifyPropertyChanged. I really like the idea of simplified code, though, and I'll keep ObserableObject in mind for other projects. I like your implementation better than that in DockPane - I may try to convince some around here with some changes, thanks! Keep up the great work!