Private Sub ComboBox8_TextChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles ComboBox8.TextChanged
        Label23.Text = ComboBox8.Text
        '2＃电弧炉状态参数设置 
        Dim i As Integer
        Dim chars As String = ComboBox8.Text
        Select Case chars
            Case "熔化期"
                ComboBox10.Items.Clear()
                For i = 1 To Val(ComboBox1.Text)
                    ComboBox10.Items.Add(i)
                Next
            Case "氧化期"
                ComboBox10.Items.Clear()
                For i = 1 To Val(ComboBox2.Text)
                    ComboBox10.Items.Add(i)
                Next
            Case "还原期"
                ComboBox10.Items.Clear()
                For i = 1 To Val(ComboBox3.Text)
                    ComboBox10.Items.Add(i)
                Next
            Case "出钢期"
                ComboBox10.Items.Clear()
                For i = 1 To Val(ComboBox19.Text)
                    ComboBox10.Items.Add(i)
                Next
        End Select
    End Sub
 运行时ComboBox9、ComboBox10没有下拉菜单？为什么？ 谢谢！！