From Xojo Documentation
Returns the row of the selected radio button.
Use SelectedCell in the SelectionChanged event to determine which radio button was clicked. Since SelectedCell is a Pair, the Left property represents the row index and the Right property represents the column index. The indexes are zero-based.
This code selects a radio button, which has the effect of de-selecting all the other radio buttons in the group:
For example, the following code in the ValueChanged event handler will display a message based upon which radio button is pressed:
Case 0 // Row 1
MessageBox("You clicked the top button.")
Case 1 // Row 2
MessageBox("You clicked the bottom button.")