Combobox เลือกข้อมูลแล้ว ข้อมูลใน textbox ไม่เปลี่ยนตามค่ะ

Private Sub f_rent_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dock = DockStyle.Fill
        'Me.cb_memid.Text = ""
        SelectData()
    End Sub

    Public Sub SelectData()
        Cnnstring = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=database/database.mdb;"
        With Conn
            If .State = ConnectionState.Open Then .Close()
            .ConnectionString = Cnnstring
            .Open()
        End With
        Dim sqluser As String = ""
        sqluser = "SELECT * FROM tb_member"

        da = New OleDbDataAdapter(sqluser, Conn)
        da.Fill(ds, "tb_member")

        If ds.Tables("tb_member").Rows.Count <> 0 Then
            IsFind = True
            With cb_memid
                '.ReadOnly = True
                .DataSource = ds.Tables("tb_member")
                .DisplayMember = "รหัสสมาชิก"
                .ValueMember = "รหัสสมาชิก"

            End With
            txt_memname.Text = CStr(ds.Tables("tb_member").Rows(0).Item("ชื่อสมาชิก"))

        Else
            IsFind = False
            cb_memid.DataSource = Nothing
        End If

    End Sub