ComboBox1.DataSource = Nothing 清空后确实没有数据了，但是加载后之前的数据又重复显示出来了，如何搞的啊

ComboBox1.DataSource = Nothing 清空后确实没有数据了，但是加载后之前的数据又重复显示出来了，怎么搞的啊？
Private Sub ComboBox1_load()
  Try
  conn = New SqlConnection("server=(local);uid=sa;pwd=;database=uuu;Integrated Security=True")
  conn.Open()
  myCommand = New SqlCommand("Select * from User", conn)
  sda.SelectCommand = myCommand
  sda.Fill(ds, "User")
  If ds.Tables(0).Rows.Count > 0 Then
  ComboBox1.DataSource = ds.Tables(0)
  ComboBox1.DisplayMember = "username"
  ComboBox1.ValueMember = "userid"
  ComboBox1.Text = ""
  'ComboBox1.SelectedValue = ""
  Else
  MsgBox("没记录")
  End If
  Catch
  MsgBox(Err.Description)
  End Try
  conn.Close()
  End Sub

  Private Sub Button6_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button6.Click
  '加载
  ComboBox1_load()
  End Sub

  Private Sub Button5_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button5.Click
  '清空
  ComboBox1.DataSource = Nothing
  ComboBox1.Items.Clear()
  End Sub

------解决方案--------------------
加载时 ComboBox1.DataSource = ds.Tables(0)，这不是又指定了datasource吗
------解决方案--------------------
你的"清空"只是UI层面的并非真正的删除数据,没有操作数据库,所以下次进来的时候还会显示
------解决方案--------------------
Private Sub Button5_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button5.Click
'清空
ds.Tables(0).rows.clear
End Sub