Refresh combobox list from other window, MVVM

Question

I\'m working on some application and I have one problem. I have two windows (Bookings - parent and Guests - child). In the parent window, I have one combo box with list of guest

Answer 1

OK, I added this lines in my "GuestsViewModel.cs":

    private BookingsViewModel _BookingsViewModel;
    public BookingsViewModel BookViewModel    // Property
    {
        get
        {
            return _BookingsViewModel;
        }
        set
        {
            _BookingsViewModel = value;
            OnPropertyChanged("BookViewModel");
        }
    }

    public GuestsViewModel(BookingsViewModel bvm)    // Constructor with one parameter
    {
        BookViewModel = bvm;
    }

    public ICommand _btnAddGuest;
    public ICommand btnAddGuest 
    {
        get
        {
            if (_btnAddGuest == null)
            {
                _btnAddGuest = new DelegateCommand(delegate()
                {
                    try
                    {
                        Service1Client wcf = new Service1Client();                           

                        wcf.AddGuest(Guest);
                        BookingsViewModel.OnPropertyChanged("Guests");    // You said to add this
                        wcf.Close();
                    }
                    catch
                    {
                        Trace.WriteLine("working...", "MyApp");
                    }
                });
            }
            return _btnAddGuest;
        }
    }

Did you mean something like this above? This don't work... I suppose I should add one more thing? Sorry, maybe this questions are stupid but I don't have idea how to solve this problem...

Regards, Vladimir