Проверьте это:
Сначала объявите это Vars:
Dim comboBoxCol As New DataGridViewComboBoxColumn
Dim gol As Integer = 0
Private Sub discountitems_new_discount_EditingControlShowing1(ByVal sender As Object, ByVal e As System.Windows.Forms.DataGridViewEditingControlShowingEventArgs) Handles discountitems_new_discount.EditingControlShowing
current_row = discountitems_new_discount.CurrentRow.Index.ToString
comboBox = CType(e.Control, ComboBox)
If (comboBox IsNot Nothing) Then
'Add the event handler.
'AddHandler comboBox.SelectedIndexChanged, New EventHandler(AddressOf ComboBox_SelectedIndexChanged)
gol = 1
AddHandler comboBox.SelectedIndexChanged, New EventHandler(AddressOf ComboBox_SelectedIndexChanged)
End If
End Sub
Private Sub ComboBox_SelectedIndexChanged(ByVal sender As Object, ByVal e As EventArgs)
comboBox = CType(sender, ComboBox)
If gol = 1 Then
Dim item_value As String = comboBox.SelectedValue 'Value
msgbox(item_value)
gol = 0
End If
End Sub