Since Q1 2010, the CheckedItems collection is not an ObservableCollection but a read only HashSet that the tree uses internally for many optimizations. You shouldn't use it to get the first or the last checked item.
It also contains both RadTreeViewItems and the business objects inside them. The CheckedItems also doesn't remove an item immediately after you uncheck it. So it is better to avoid using it. Instead, you can bind the IsChecked property of the RadTreeViewitem to a boolean property of your ViewModel using ContainerBindings
. You can also have properties in your tree`s ViewModel that hold the first Checked item or last Checked item and set/unset(reset) them via the Checked/UnChecked event handler of the RadTreeView.
Hope this info helps you. Feel free to ask if you need further assistance.
the Telerik team
Registration for Q1 2011 What’s New Webinar Week is now open. Mark your calendar for the week starting March 21st and book your seat
for a walk through all the exciting stuff we ship with the new release!