How can I extend a ComboBox to support commands (MVVM)?

As topic says, I need to extend the features of a standard Silverlight ComboBox to also support Commanding. Since I follow MVVM I need my ComboBox to communicate the SelectionChanged event to my ViewModel.

What would the code look like for doing this? I want to be able to put th开发者_如何学JAVAe Command attribute on my ComboBox XAML control.

Using (WCF RIA, MVVM, VB.NET)..

All tips appricated!

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You can bind the property SelectedIndex or SelectedItem of the Combobox to your ViewModel. So you don´t need any Commands.

Example (Binding to SelectedIndex):

XAML

<ComboBox SelectedIndex="{Binding SelectedIndex, Mode=TwoWay}"/>

C#

public class ComboBoxViewModel
{
   private int _selectedIndex;
   public int SelectedIndex {
     get { return _selectedIndex; }
     set { 
       if (value != _selectedIndex) {
         _selectedIndex = value;
         // Perform any logic, when the SelectedIndex changes (aka. PropertyChanged-Notification)
       }
     } 
   }
}

Example (Binding to SelectedItem):

XAML

<ComboBox SelectedItem="{Binding SelectedItem, Mode=TwoWay}"/>

C#

public class ComboBoxViewModel
{
   private MyViewModel _selectedItem;
   public MyViewModel SelectedItem {
     get { return _selectedItem; }
     set { 
       if (value != _selectedItem) {
         _selectedItem= value;
         // Perform any logic, when the SelectedIndex changes ((aka. PropertyChanged-Notification)
       }
     } 
   }
}

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Create a behavior that exposes an ICommand Command and a object CommandParameter. In the behavior wire up to the SelectionChanged event of your AssociatedObject. Then you can bind the command to your behavior and simulate a command for the SelectionChanged event.