MVVM toolkit in a screenful of code

MVVMToolkit.cs

namespace MVVMToolkit
{
    public abstract class ObservableObject : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;

        protected void OnPropertyChanged(string propertyName)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    public class RelayCommand : ICommand
    {
        readonly Action<object> action;
        readonly Predicate<object> canExecute;        
        
        public RelayCommand(Action<object> execute) : this(execute, null) { }
        
        public RelayCommand(Action<object> action, Predicate<object> canExecute)
        {
            this.action = action ?? throw new ArgumentNullException("execute");
            this.canExecute = canExecute;           
        }
        
        public bool CanExecute(object parameters)
        {
            return canExecute == null ? true : canExecute(parameters);
        }

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

        public void Execute(object parameters)
        {
            action(parameters);
        }        
    }

}