Updating a GUI element when datasource changes

I have a silverlight app and a listbox in it whic I populate using:

listItems.ItemsSource = App.AvailableProductLi开发者_StackOverflow社区st;

If i then add an element to the AvailableProductList, the listbox will NOT be automatically updated. Does anyone knows how to update the listbox?

tks, Oscar

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I was using the List, I changed to ObservableCollection and it worked :)

Tks!