ListBox.SelectedRowValue
From Xojo Documentation
Property (As String )
aListBox.SelectedRowValue = newStringValue
or
StringValue = aListBox.SelectedRowValue
New in 2019r2
Supported for all project types and targets.
or
StringValue = aListBox.SelectedRowValue
New in 2019r2
Supported for all project types and targets.
The value of the currently selected item.
Notes
In the case of multi-column ListBoxes, the value of the cell in the first column is returned.