Silverlight 4 MVVM: Unable to Databind ICommand

Question

I have created a Silverlight User Control. The markup is:

<StackPanel Grid.Row="4" Grid.Column="0" Orientation="Horizontal" Width="Auto" Margin="5">
    <Button Content="OK" Margin="0,0,5,5" MinWidth="50" Command="{Binding OKCommand}"  />
</StackPanel>

The code behind declares a Dependency property 'OKCommand' as:

public ICommand OKCommand
{
    get
    {
        return (ICommand)GetValue(OKCommandProperty);
    }
    set
    {
        SetValue(OKCommandProperty, value);
    }
}

public static readonly DependencyProperty OKCommandProperty
    = DependencyProperty.Register("OKCommand", typeof(ICommand), typeof(TestUserControl), new PropertyMetadata(null, OKCommandProperty_PropertyChangedCallback));

private static void  OKCommandProperty_PropertyChangedCallback(DependencyObject d, DependencyPropertyChangedEventArgs e)
{      
}

Now I want to use the user control on another page where which is the View & the ViewModel defines the command to which I want the OKCommand to be bound. The XAML markup is as such:

<local:TestControl OKCommand="{Binding Path=TestControlOk}"/>

However when I click the button it does not execute anything. Any clues as to what I am doing wrong here.

Answer 1

You need to show the view model that contains the TestControlOk property so we can tell if that's part of the problem.

---

UserControls do not register themselves as the data context automatically so the binding inside the user control won't have anything to bind to. Do you have

this.DataContext = this;

anywhere in the UserControl codebehind to enable your first binding to actually work?

Alternatively, you can do something like so:

<UserControl .....
    x:Name="MyUserControl">
    <StackPanel Grid.Row="4" Grid.Column="0" Orientation="Horizontal" Width="Auto" Margin="5">
        <Button Content="OK" Margin="0,0,5,5" MinWidth="50" 
            Command="{Binding OKCommand, ElementName=MyUserControl}"  />
    </StackPanel>
</UserControl>

Note the ElementName= part of the binding pointing to the root UserControl element in your XAML.