帮我看看有什么问题 谢谢了

Imports System.Data.OleDbPublic Class Form1   Private Sub Form1_Load(ByVal sender As System.Object, _   ByVal e As System.EventArgs) Handles MyBase.Load   Dim con As OleDbConnection = New OleDbConnection( _   "Provider=Microsoft.jet.oledb.4.0;data source=E:\我的项目\图书管理信息系统\图书管理信息系统\book.mdb")   Dim cmd As OleDbCommand = New _   OleDbCommand("SELECT book_name,book_id FROM book_info", con)   con.Open()   Dim myDA As OleDbDataAdapter = New OleDbDataAdapter(cmd)   Dim myDataSet As DataSet = New DataSet()   myDA.Fill(myDataSet, "MyTable")   '第一种   ComboBox1.DataSource = myDataSet.Tables("MyTable").DefaultView   ComboBox1.ValueMember = "book_name"   ComboBox1.DisplayMember = "book_info"   ' 第二种   'For Each dRow As DataRow In myDataSet.Tables("MyTable").Rows   ' ComboBox1.Items.Add(dRow.Item("Username"))   'Next   con.Close()   con = Nothing
   End Sub
   Private Sub ComboBox1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ComboBox1.SelectedIndexChanged   TextBox1.Text = ComboBox1.SelectedValue
   End SubEnd Class