design patterns - WPF MVVM : Commands are easy. How to Connect View and ViewModel with RoutedEvent

Question

Suppose I have a view implemented as a DataTempate inside a resource Dictionary. And I have a corresponding ViewModel. Binding Commands are easy. But what if my View contains a control such as a ListBox, and I need to Publish an application wide event (Using Prism's Event Aggreagtor) based on the Item being Changed on the List.

if ListBox supports a command I could just bind it to a command in the ViewModel and publish the event. But Listbox doesn't allow such an option. How do I bridge this?

EDIT: Many great answers.

Take a look at this link http://blogs.microsoft.co.il/blogs/tomershamam/archive/2009/04/14/wpf-commands-everywhere.aspx

Thanks

Ariel

Answer 1

Instead of trying to bind a command to when the item changes, I looked at the problem another way.

If you bind the selected item of the ListBox to a property in the ViewModel, then when that property is changed you can publish the event. That way the ViewModel remains the source of the event and it is triggered by the item changing, which is what you want.

<ListBox ItemsSource="{Binding Items}" SelectedItem="{Binding SelectedItem}" />

...

public class ViewModel
{
    public IEnumerable<Item> Items { get; set; } 

    private Item selectedItem;
    public Item SelectedItem
    {
        get { return selectedItem; }
        set
        {
            if (selectedItem == value)
                return;
            selectedItem = value;
            // Publish event when the selected item changes
        }
}