How can I update a property of mainWindowViewModel from another ViewModel? - wpf

Question

From mainWIndow.xaml, which uses as DataContext the mainWindowViewModel, I opening a new window with name addNewItem.xaml, which uses as DataContext the ItemsViewModel.
In addNewItem.xaml I have a DataGrid
<DataGrid SelectedItem="{Binding Path=SelectedHotel}" ItemsSource="{Binding HotelsList}" AutoGenerateColumns="False">
<DataGrid.Columns>
<DataGridTemplateColumn Width="350" Header="Hotel" IsReadOnly="True">
<DataGridTemplateColumn.CellTemplate>
<DataTemplate>
<Label Content="{Binding Path=Name}"></Label>
</DataTemplate>
</DataGridTemplateColumn.CellTemplate>
</DataGridTemplateColumn>
</DataGrid.Columns>
</DataGrid>
I want to pass the SelectedHotel from ItemsViewModel to mainWindowViewModel.
I tried to do this with the following code (with no luck)
//This is a property from ItemsViewModel
private Hotel _selectedHotel { get; set; }
public Hotel SelectedHotel {
get { return _selectedHotel; }
set {
_selectedHotel = value;
RaisePropertyChanged("SelectedHotel");
OnSelectedItemChanged();
}
}
void OnSelectedItemChanged() {
MainWIndowViewModel = new MainWIndowViewModel(this.SelectedHotel);
}
In mainWIndowViewModel I have also one more Property (with same name, SelectedHotel) which it gets value through the constructor
public MainWIndowViewModel(Hotel selectedHotel)
: this(new ModalDialogService()) {
this.SelectedHotel = selectedHotel;
}
In mainWindow.xaml I want to display a value of the property
<Label Content="{Binding SelectedHotel.Name}" DockPanel.Dock="Top"></Label>
what am I doing wrong?
In general, I need to know the rule of doing something like this.
How could I notify a property from another property?
Thanks
Solution
I solve it with messages from mvvm light.

Answer 1

Finally I found a solution and this comes from mediator pattern. I use the mvvmLight.
From mainWindowViewModel, I registered a message (I don't know if the term of message is the correct one)
public MainWIndowViewModel(IDialogService dialog) {
this._dialog = dialog;
Messenger.Default.Register<NotificationMessage<Hotel>>(this, NotificationMessageReceived);
}
private void NotificationMessageReceived(NotificationMessage<Hotel> selectedHotel) {
this.SelectedHotel = selectedHotel.Content;
}
from the other viewModel, I send a message with the SelectedHotel.
private Hotel _selectedHotel { get; set; }
public Hotel SelectedHotel {
get { return _selectedHotel; }
set {
_selectedHotel = value;
RaisePropertyChanged("SelectedHotel");
Messenger.Default.Send(new NotificationMessage<Hotel>(this, SelectedHotel, "SelectedHotel"));
}
}

Answer 2

In the ItemsViewModel you do not need the OnSelecetedItemChanged handler code at all. Instead, in the MainWindowViewModel store a reference to the ItemsViewModel, and add a handler there:
var ItemsViewModel = itemsVM = new ItemsViewModel();
itemsVm.PropertyChanged += SelectedHotelChanged;
// and then implement the handler:
public void SelectedHotelChanged(object sender, PropertyChangedEventArgs args)
{
SelectedHotel = itemsVM.SelectedHotel;
}
// ensuring that the SelectedHotel property in the MainWindowViewModel also notifies when it changes.
Edit: Fixed a typo.