public partial class Default4 : System.Web.UI.Page
{
    private SqlConnection conn;
    private SqlCommand cmd;
    private SqlDataReader reader;
    protected void Page_Load(object sender, EventArgs e)
    {
        if(!IsPostBack)
            AddOnPreRenderCompleteAsync(new BeginEventHandler(BeginAsyncOperation), new EndEventHandler(EndAsyncOperation));

    }
    IAsyncResult BeginAsyncOperation(object sender, EventArgs e, AsyncCallback cb, object state)
    {
        string str = System.Web.Configuration.WebConfigurationManager.ConnectionStrings["GtKydjConnectionString"].ConnectionString;
        SqlConnection conn = new SqlConnection(str);
        cmd = new SqlCommand("select * from GtKydj", conn);
        conn.Open();
        return cmd.BeginExecuteReader(cb, state);
    }
    void EndAsyncOperation(IAsyncResult ar)
    {
        reader = cmd.EndExecuteReader(ar);
        GridView1.DataSource = reader;
        GridView1.DataBind();
    }
    public override void Dispose()
    {
        if (conn != null)
            conn.Close();
        base.Dispose();
    }
}