In this example, the BeforeLineChange event checks the value of the Markdown Amount field in the Invoice Entry grid. If the user attempts to enter a markdown amount greater than 20%, the KeepFocus parameter stops the line change event, and moves the focus back to the current line:
Private Sub Grid_BeforeLineChange(KeepFocus As Boolean) If CCur(MarkdownAmount) > CCur(UnitPrice) * 0.2 Then 'The markdown was greater than 20% KeepFocus = True MsgBox "You cannot enter a markdown greater than 20% " + _ "of the unit price." End If End Sub