Question

I have a custom user control extending the Listbox class. Inside of it I am overriding OnSelectionChanged to add/remove Adorners to any selected/unselected items. This all works when I select an item using the mouse, but when I programmatically add items to the listbox using

myListBox.SelectedItems.Add(newItem) // newItem is already a member of myListBox.Items

It does not execute the OnSelectionChanged code.

Update: Unless I’m crazy (which is always possible) it seems there is a difference in behaviour between calling this from the parent object

myListBox.SelectedItems.Add(newItem)

and this method inside my extended listbox class

Public Sub AddSelectedItem(newItem as Object)
    Me.SelectedItems.Add(newItem)
End Sub

For some reason the second option is triggering the event while the first one isn’t.

Answer 1

The solution here is that calling SelectedItems.Add() from inside an extension of ListBox

public class MyListBox : ListBox
{
public void AddSelectedItems(object newSelectedItem)
{
  // works
  this.SelectedItems.Add(newSelectedItem);
}
}

will trigger the OnSelectionChanged event.

Calling it like this from the window will not trigger the event

private sub SomeWindowMethod()
{
   // does not work
   this.MyListBoxInstance.SelectedItems.Add(newSelectedItem);
}