Combo Box in Silverlight 4

I have a combo box that is bound to a collection that is essentially a list of Name/Value pairs. The collection can have multiple items with different names, but the values may be the same.

public class NameValuePair
{
   public string Name { get; set; }
   public string Value { get; set; }
}

public class NameValuePairCollection : List<NameValuePair>
{
   public NameValuePairCollection(): base() { }
}

So inside my User Control I have a private field called items which is an instance of that NameValuePai开发者_开发知识库r collection:

private NameValuePairCollection items = new NameValuePairCollection()

Somewhere along the lines that collection gets initialized and items get added to it. However, the problem I see is when I try to set the selected index of the combo box that is bound to this collection:

this.CboItemsSelector.SelectedIndex = 3;

or

this.CboItemsSelector.SelectedItem = this.items[3];

The selected item is there but the UI is not synchronized. The UI's selector still defaults to the first item in the list, even thought the SelectedItem's Name and Value properties DO IN FACT CORRESPOND to whatever is in index 3 of the underlying collection!

Any ideas on how to force the ComboBox to refresh itself? Or just plain fix the issue? I know it's quite small issue, but it is big enough to force me to rewrite quite a bit of code.... :( :( :(

Thanks!

You need to inherit from ObservableCollection, not List. Otherwise no OnPropertyChanged events will be fired and the bound control wont know the data has been updated.

Do the selected Item's Name and Value properties match or is the SelectedItem an instance from within the same collection? .Net will not know to compare the items by name and value unless you tell it to, else it will use object equality to try and find the item in your list. If you are setting the selected item to an instance that is not actually in the list (but has the same properties) .net will not find it in the list. You have 2 options, override equality for your object and force comparison of properties, or ensure that you always set the selected item to an item in the list. Also try what Andy May suggested and do 2 way binding on the ItemsSource and on the SelectedItem, should work then