Databound WPF ComboBox with 'New...' item

Hi all

I have a combobox which is databound to a list of elements. But in addition to that list of elements, i want to have another item. This item should display the text 'New...'

The idea is if they select one of the normal el开发者_运维问答ements, it performs some action involving that element. If they select the 'New' element, it will take them to a screen where they can create a new item.

The problem is, When you databind something you dont get the option to add another item to it, and there is no question of adding a dummy item to the list of elements...

Is this an opportunity to create a new control based on the ComboBox which has a 'DefaultElement' property? (with all of the associated templating and command binding etc)

To do this I have previously created a dummy wrapper class for the normal type, allowing you to bind to a list containing mostly the correct values and also your "New..." one, e.g.

public class DisplayClass
{
    public DisplayClass(ModelClass mc)
    {
         this.mc = mc;
    }

    public string Name
    {
        get { return this.mc != null ? this.mc.Name : "New..."; }
    }

    public bool IsDummy
    {
        return this.mc == null;
    }

    public ModelClass Model
    {
        return this.mc;
    }
}

You can then host a collection of these in your data context (ViewModel), and handle the selection appropriately based on IsDummy. It's not as automatic as a control with this functionality built in, but is pretty simple and could probably easily be made generic and so reusable.

Set the ItemsSource property to a CompositeCollection with the new item and bound collection together, then detect that item's selection based on selected index or something similar.

Example Code:

<ComboBox>
   <ComboBox.ItemsSource>
      <CompositeCollection>
         <ComboBoxItem>Add New Item...</ComboBoxItem>
         <CollectionContainer Collection="{Binding Source={StaticResource CollectionSource}}"/>
      </CompositeCollection>
   </ComboBox.ItemsSource>
</ComboBox>

MSDN for CompositeCollection: http://msdn.microsoft.com/en-us/library/system.windows.data.compositecollection(v=vs.110).aspx

Keep in mind that what you bind to is a UI oriented collection of items which can be different than the business or data entities.

If I were you, I'd insert a 'new' entity in the first position of the bound collection and detect it in my viewmodel to trigger the appropriate action when the user selects it.