How to use the MVVM RelayCommand Attribute?

Question

I have been trying out attributes and ran in an issue trying to use the RelayCommand attribute from the Community Toolkit.

I looked over the .NET Documentation on RelayCommand Attribute and tried to implement a simple example as follows:

using CommunityToolkit.Mvvm.ComponentModel;
using CommunityToolkit.Mvvm.Input;

namespace HelloWorld_WinUI3.ViewModels;

public partial class MainViewModel : ObservableObject
{
    public MainViewModel()
    {
    }

    private int _counter = 0;

    [RelayCommand]
    private async Task DoSomethingAsync()
    {
        await Task.Delay(1000);
        MyString = $"Hello {_counter++}";
    }

    [ObservableProperty]
    private string _myString = "Hello"; 
}

This produces the error: CS0616 'RelayCommand' is not an attribute class

Can someone explain what is wrong with this code and how to use the [RelayCommand] attribute properly?

Answer 1

The CommunityToolkit.Mvvm works with WinUI 3 and.NET7. Actually, I use it a lot, including every sample I create for StackOverflow answers.

I guess, you might be facing this known issue.

So, at this moment, try the v8.0 instead of v8.1.