A command whose sole purpose is to relay its functionality to other objects by invoking delegates. The default return value for the CanExecute method is ''.
Inheritance: ICommand
 /// <summary>
 /// Initializes a new instance of the SimpleViewModel class.
 /// Wires up all the Window based Lifetime commands.
 /// </summary>
 protected SimpleViewModel()
 {
     _activatedCommand = new RelayCommand(p => OnWindowActivated());
     _deactivatedCommand = new RelayCommand(p => OnWindowDeactivated());
     _loadedCommand = new RelayCommand(p => OnWindowLoaded());
     _unloadedCommand = new RelayCommand(p => OnWindowUnloaded());
     _closeCommand = new RelayCommand(p => OnWindowClose());
 }