Disable WPF buttons during longer running process, the MVVM way

Question

I have a WPF/MVVM app, which consists of one window with a few buttons.
Each of the buttons triggers a call to an external device (an USB missile launcher), which takes

Answer 1

I think this is a bit more elegant:

XAML:

C# (using async & await):

public class MainWindowViewModel : INotifyPropertyChanged
{
    private bool isGuiEnabled;

    /// 

    /// True to enable buttons, false to disable buttons.
    /// 
    public bool IsGuiEnabled 
    {
        get
        {
            return isGuiEnabled;
        }
        set
        {
            isGuiEnabled = value;
            OnPropertyChanged("IsGuiEnabled");
        }
    }

    public ICommand DeviceCommand
    {
        get
        {
            return new RelayCommand(this.CallExternalDevice, this.IsGuiEnabled);
        }
    }

    private async void CallExternalDevice(object obj)
    {
        IsGuiEnabled = false;
        try
        {
            await Task.Factory.StartNew(() => Thread.Sleep(3000));
        }
        finally
        {
            IsGuiEnabled = true; 
        }
    }
}