Add-Type -AssemblyName PresentationFramework

# INotifyPropertyChanged Basisklasse fuer alle ViewModels
Add-Type @"
using System;
using System.ComponentModel;
using System.Windows.Input;

namespace FirefoxAddinManager {

    public class ObservableBase : INotifyPropertyChanged {
        public event PropertyChangedEventHandler PropertyChanged;
        protected void OnPropertyChanged(string name) {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));
        }
    }

    public class RelayCommand : ICommand {
        private readonly Action<object> _execute;
        private readonly Func<object, bool> _canExecute;

        public RelayCommand(Action<object> execute, Func<object, bool> canExecute = null) {
            _execute    = execute ?? throw new ArgumentNullException(nameof(execute));
            _canExecute = canExecute;
        }

        public event EventHandler CanExecuteChanged {
            add    { System.Windows.Input.CommandManager.RequerySuggested += value; }
            remove { System.Windows.Input.CommandManager.RequerySuggested -= value; }
        }

        public bool CanExecute(object parameter) => _canExecute == null || _canExecute(parameter);
        public void Execute(object parameter) => _execute(parameter);
    }
}
"@ -ReferencedAssemblies PresentationFramework, PresentationCore, WindowsBase