VB.NET数据循环显示

Imports System.Data
Imports System.Data.SqlClient
 
Public Class Form1
    Dim cn As SqlConnection
    Dim ml As SqlDataAdapter
    Dim am As SqlCommand
    Dim ds As DataSet
    Dim at As String
    Private itms As Integer
    Private itm As Integer

    Private Sub InitializeTimer()
        itms = 0
        itm = 4

    End Sub
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load


        Dim cnm As String = "Data Source=(local);Initial Catalog=DB_1001;Integrated Security=False;User ID=sa;Password=123;"
        cn = New SqlConnection(cnm)

        Timer1.Enabled = True
        DataGridView1.AllowUserToAddRows = False
        DataGridView1.RowHeadersVisible = False
    End Sub


    Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
        itm = 6
        If itms < 15 Then
            Timer1.Interval = 2000

            Dim sql As String = "select top (" + Convert.ToString(itm) + ") id,names,email from aatest where id not in(select top(" + Convert.ToString(itms) + ") id from aatest) "
            ml = New SqlDataAdapter(sql, cn)
            ds = New DataSet
            ml.Fill(ds, "abc")
            DataGridView1.DataSource = ds.Tables("abc")
            itms = itms + 6
            DataGridView1.AutoGenerateColumns = False
            If itms >= 15 Then
                itms = 0
            End If
        End If


    End Sub
End Class