From Xojo Documentation
The number of the last row added with the AddRow, AddExpandableRow, or AddRowAt method. LastAddedRowIndex is zero-based. If no rows have been added, LastAddedRowIndex will be the ListBox.None constant (-1). Use this to get the row number when getting or setting values in a multi-column ListBox. See the section on Multi-column listboxes in the Notes section.
This example project consists of a two-column ListBox and two TextFields for the entry of first and last names. A PushButton creates a new row in the ListBox and adds the contents of the TextFields to the ListBox.
PeopleList.CellValueAt(PeopleList.LastAddedRowIndex, 0) = FirstNameField.Value
PeopleList.CellValueAt(PeopleList.LastAddedRowIndex, 1) = LastNameField.Value
PeopleList.SelectedIndex = PeopleList.LastAddedRowIndex // select the newly added row
This code asks the user to add a row if they have not yet done so: