How do I update the items in a dropdownList or listBox?

rollout test "Test"
(
listBox testList items:#("Item 1","Item 2")
button addToList "Add Item To End Of List" width:180
button insertToList "Insert Before Current Item" width:180
button removeFromList "Remove Current Item" width:180
--Append a new Item to the array. Since append returns the resuling array,
--it is OK to assign the result directly to the .items property
on addToList pressed do
  testList.items = append testList.items ("Item "+ (testList.items.count+1) as string)
--Instert new item before current item
on insertToList pressed do
(
  --Check whether current item selection exists (greater than 0)
  if testList.selection > 0 do
  (
    --Because insertItem returns OK instead of the resulting array,
    --you cannot assign the result of the expression directly to the property.
    --Instead, you have to get a copy of the items array in a local variable...
    temp_array = testList.items
    --...perform the insertion with the temp. array in the local variable...
    insertItem ("Item "+ (testList.items.count+1) as string) temp_array testList.selection
    --...and assign back the temp. array to the .items property
    testList.items = temp_array
  )
)
--Remove currently selected item from the list:
on removeFromList pressed do
(
  --Check whether there are any items left and there is a valid selection.
  --Then delete the current item. DeleteItem returns the resulting array,
  --so you can assign the result directly to the .items property
  if testList.items.count > 0 and testList.selection > 0 do
    testList.items = deleteItem testList.items testList.selection
)
)
createDialog test 200 220