ReactiveUI and CanExecute: How to validate boolean variables

Question

Because of AvaloniaUI I am confronted with ReactiveCommands. While the excecution part is quite easy, I would like to manage the canexecute part. In particular, I need to check some boolean properties of a socket. As they change asynchronously, I would like to enable or disable a button accordingly. Lets say:

public class MainViewModel : ViewModelBase
{
    public MainViewModel()
    {
        OnButton_Clicked = ReactiveCommand.Create(OnButtonClicked, CanClickButton);
    }
    
    private Socket Socket { get; set; }
    
    public ReactiveCommand<Unit, Unit> OnDiscover_Clicked { get; }
    
    private void OnButtonClicked()
    {
        // Do something
    }
    
    private bool CanClickButton()
    {
        return Socket?IsAvailable;
    }
}

Of course, it doesn't work like that. ReactiveCommand requieres some observeable object, which in turn seems to rely on IPropertyChanged, but that again is not provided by the Socket. How can I achieve a periodic check of a boolean variable in the canexecute function?

Answer 1

Like you stated in your question the ReactiveCommand requires an IObservable<bool>

public class MainViewModel : ViewModelBase
{
    public MainViewModel()
    {
        IObservable<bool> canExecute = this.WhenAnyValue(x => x.Socket.IsAvailable);
        OnDiscover_Clicked = ReactiveCommand.Create(OnButtonClicked, canExecute);
    }

    private Socket Socket { get; set;     }

    public ReactiveCommand<Unit, Unit> OnDiscover_Clicked { get; }

    private void OnButtonClicked()
    {
        // Do something
    }
}

Note that your socket class needs to implement INotifyPropertyChanged in order for this.WhenAnyValue to work, so you could create something like a SocketViewModel which wraps the socket.