主题：dropdownbox

Dim drp As WinForm.DropDownBox = e.Sender
Dim vals As String() = {"工商银行","建设银行","农业银行","中国银行"}
Dim val As String = drp.value
Dim index As Integer = -1
For i As Integer = 0 To vals.Length - 1
    If val = vals(i) Then
        index = i
        Exit For
    End If
Next
index = index + 1
If index > 3 Then
    index = 0
End If
drp.Value = vals(Index)

上面的代码是要用微调按钮来进行选择的。如果我不用微调按钮，就用下拉按钮进行选择，请问要怎样修改代码？谢谢。