ListBox.AddExpandableRowAt
From Xojo Documentation
Method
ListBox.AddExpandableRowAt(rowNumber as Integer, Item as String, [Indent as Integer])
New in 2019r2
Supported for all project types and targets.
New in 2019r2
Supported for all project types and targets.
Creates a new expandable row at row (zero-based), moving the existing rows down. The text is always assigned to column zero. The optional parameter indent specifies the amount of indentation of the row in a ListBox where AllowExpandableRows (sometimes called a hierarchical ListBox) is True. The default is zero. It has no effect on a ListBoxe where AllowExpandableRows is False.
Example
The following example in a PushButton adds a row to the ListBox with expandable rows that is used for the example in AddExpandableRow. It simply adds a new state to the list of cities and states.
Listbox1.AddExpandableRowAt(1, "New Hampshire")