Question

I’m having difficulty getting the binding to fire off on a user control that is nested inside of another use control.
Here is my hierarchy:

• Navigation Page
  • User Control A (AthleteMaxGrid)
    • User Control B (PagingControl)

I’m using the MVVM design model with the MVVMLight toolkit for these controls.
Here is the situation:
Both User Controls have corresponding ViewModels that are attached to them in the XAML.
The View Model of AthleteMaxGrid has a Observable Collection (AthleteMaxes) property exposed that I wanted to bind to the PagingControl. This property is also being bound to in a dataview in the AthleteMaxGrid control, so it know its being populated correctly.

Here is the code:

AthleteMaxGrid XAML:

     <UserControl ...
         DataContext="{Binding AthleteMaxGrid, Source={StaticResource Locator}}">
     ....
     <StackPanel Orientation="Horizontal">
        ...
        <my:PagingControl Jake="{Binding AthleteMaxes}" />
    </StackPanel>
    <telerik:RadGridView x:Name="rgvMaxes" IsScrolling="False" 
        ItemsSource="{Binding AthleteMaxes}" AutoGenerateColumns="False" 
        IsBusy="{Binding IsBusy}" >...

Here is a snipit from the AthleteMaxGrid ViewModel:

public const string AllMaxesPropertyName = "AthleteMaxes";

private ObservableCollection<AthleteMaxTableItem> _allMaxes = new ObservableCollection<AthleteMaxTableItem>();

    /// <summary>
    /// Gets the AthleteMaxes property.
    /// </summary>
    public ObservableCollection<AthleteMaxTableItem> AthleteMaxes
    {
        get
        {
            return _allMaxes;
        }

        set
        {
            if (_allMaxes == value)
            {
                return;
            }

            _allMaxes = value;

            // Update bindings, no broadcast
            RaisePropertyChanged("AthleteMaxes");
        }
    }

Here is the XAML from PagingControl:

<UserControl  ...
          x:Name="rootElement"
         DataContext="{Binding PagingControlVM, Source={StaticResource Locator}}">
 ...
</UserControl>

And I created the Dependency property in the PagingControl code behind like this:

    public const string JakePropertyName = "Jake";

    public object Jake
    {
        get
        {
            return (object)GetValue(JakeProperty);
        }
        set
        {
            SetValue(JakeProperty, value);
        }
    }

    public static readonly DependencyProperty JakeProperty = DependencyProperty.Register(
        JakePropertyName,
        typeof(object),
        typeof(PagingControl),
        new PropertyMetadata(null,
            new PropertyChangedCallback(onJakeChanged)));


    private static void onJakeChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        MessageBox.Show(d.GetType().ToString());
    }

At this point i’m just trying to get my Callback function hit (onJakeChanged) so I know the data is coming in properly and I can move to the next stage of binding my controls, however it is not getting hit.

If I set the Jake Property in the XAML on the AthleteMaxGrid to something simple like “test” then the callback is hit properly. It seems to be a problem with the binding of the viewModel property.

Any ideas?

Thanks in advance!
Nick

Answer 1

This one is simple to answer. This line here:

<my:PagingControl Jake="{Binding AthleteMaxes}" />

will bind Jake to the DataContext’s AthleteMaxes. But you are setting the DataContext to something else when the UserControl is created!

<UserControl x:Name="rootElement" DataContext="{Binding PagingControlVM, Source=StaticResource Locator}}">

So now Jake is bound to PagingControlVM.AthleteMaxes … which doesn’t exist 🙂