DataGridView的更新问题,急!急!急!

我的页面上只有一个DataGridView和一个Button,想通过OleDbDataAdapter.Update更新ACCESS表里的值,不知我的代码错在那里,一直不能更新效果,请高手帮忙!
我的代码:
Imports System.Data
Imports System.Data.OleDb
Imports System.Data.Odbc
Public Class Form1

Dim objConn As New OleDbConnection
Dim objAdap As OleDbDataAdapter
Dim objDs As New DataSet
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

Dim db As New DB
objConn = db.CreateCon() '这里创建一个连接

Dim strSql = "Select * From test"
objAdap = New OleDbDataAdapter(strSql, objConn)

Dim builder As OleDbCommandBuilder
builder = New OleDbCommandBuilder(objAdap)

objAdap.Fill(objDs, "tt")
DataGridView1.DataSource = objDs.Tables("tt")
objConn.Close()

End Sub

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
'点击按钮更新
objAdap.Update(objDs, "tt")
objDs.AcceptChanges()
objConn.Close()
MessageBox.Show("Update OK")
End Sub
End Class