Silverlight: Parent ViewModel Property value to Child ViewModel property - silverlight-5.0

Question

I posted this question on the Silverlight forums, but haven't been able to get an answer to solve my issue, so I hope the guru's at SO can help!
Basically I have an entity property in my parent viewmodel. When this entity changes I need the ID of the entity in my child viewmodel. I have created a child control with a dependency property and created a binding in the constructor. I am trying to implement all this using MVVM and MEF.
My ParentViewModel:
[ExportPlugin(ViewModelTypes.ParentViewModel, PluginType.ViewModel)]
[PartCreationPolicy(CreationPolicy.NonShared)]
public class ParentViewModel: ViewModelBase
{
private Person _currentPerson;
public Person CurrentPerson
{
get { return _currentPerson; }
private set
{
if (!ReferenceEquals(_currentPerson, value))
{
_currentPerson= value;
RaisePropertyChanged("CurrentPerson");
}
}
}
}
My ParentUserControl:
<UserControl x:Class="MyApp.ParentUserControl" x:Name="ParentControl">
<local:ChildUserControl PersonID="{Binding ElementName=ParentControl, Mode=TwoWay, Path=DataContext.CurrentPerson.ID}" />
</UserControl>
My ChildUserControl codebehind:
public partial class ChildUserControl : UserControl
{
#region Private Properties
private PluginCatalogService _catalogService = PluginCatalogService.Instance;
#endregion
#region Dependency Properties
public static readonly DependencyProperty PersonIDProperty =
DependencyProperty.Register("PersonID", typeof(int), typeof(ChildUserControl), new PropertyMetadata(OnPersonIDChanged));
#endregion
#region Public Properties
public int PersonID
{
get { return (int)GetValue(PersonIDProperty); }
set { SetValue(PersonIDProperty, value); }
}
#endregion
#region Constructor
public ChildUserControl()
{
InitializeComponent();
if (!ViewModelBase.IsInDesignModeStatic)
this.DataContext = _catalogService.FindPlugin(ViewModelTypes.ChildViewModel, PluginType.ViewModel);
this.SetBinding(PersonIDProperty, new Binding("PersonID") { Mode = BindingMode.TwoWay, Source = DataContext, UpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged });
}
#endregion
private static void OnPersonIDChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
...
}
My ChildViewModel:
[ExportPlugin(ViewModelTypes.ChildViewModel, PluginType.ViewModel)]
[PartCreationPolicy(CreationPolicy.NonShared)]
public class ChildViewModel: ViewModelBase
{
private int _personID;
public int PersonID
{
get { return _personID; }
set
{
if (!ReferenceEquals(_personID, value))
{
_personID= value;
RaisePropertyChanged("PersonID");
}
}
}
}
I created the OnPersonIDChanged event to see if when the CurrentPerson entity changed, the change was being picked up in the ChildControl, which it is. It just isn't being picked up in the ChildControl ViewModel.
Any help is much appreciated.

Answer 1

Preferably, if you are using PRISM you can use the EventAggregator...
see http://msdn.microsoft.com/en-us/library/ff921122(v=pandp.40).aspx and https://compositewpf.codeplex.com/
Another option would be to hook (hack) onto the PropertyChanged
ViewModel1.PropertyChanged += (s, e) =>
{
if (e.PropertyName == "XXX")
{
ViewModel2.PropertyX = vm1.PropertY;
}
};