VB.NET 异步读取数据方法之二

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Imports System.Data.SqlClient
Imports System.Threading

Public Class FrmMain

    Private Sub btnLoad_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnLoad.Click
        Dim cn As New SqlConnection                                                                                                        ’定义连结字符串，并且要注意加ASYNCHRONOUS PROCESSING=TRUE
        cn.ConnectionString = "Data Source=WANGLI;Initial Catalog=PlcData;Persist Security Info=True;User ID=sa;pwd=sa;Asynchronous processing=true"

cn.Open()

Dim strSql As String = "select * from tbdata"
Dim mycommand As New SqlCommand(strSql, cn)

Dim itfAsynch As IAsyncResult ’定义一个异步读取变量
itfAsynch = mycommand.BeginExecuteReader(CommandBehavior.CloseConnection) ’执行异步读写

        While Not itfAsynch.IsCompleted                                                                                                        ’ 等待执行,
            Console.WriteLine("Working on main thread...")
            Thread.Sleep(1000)
        End While

Console.WriteLine()

        Dim dt As New DataTable                                                                                                                   ’执行完结后将数据写入datatable中
        Dim MydataReader As SqlDataReader = mycommand.EndExecuteReader(itfAsynch)
        'While MydataReader.Read
        '    Console.WriteLine("序号:" & MydataReader(0).ToString)
        'End While
        dt.Load(MydataReader)
        DataGridView1.DataSource = dt

MydataReader.Close()

Console.ReadLine()

End Sub
End Class