asp.net ajax 留言板

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;

public partial class 留言板 : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            string sql = ConfigurationManager.ConnectionStrings["strcnn"].ConnectionString;
            using (SqlConnection sqlcnn = new SqlConnection(sql))
            {
                SqlCommand sqlcmm = sqlcnn.CreateCommand();
                sqlcmm.CommandText = "select [content] from chat";
                sqlcnn.Open();
                SqlDataReader reader = sqlcmm.ExecuteReader();
                if (reader.HasRows)
                {
                    while (reader.Read())
                    {
                        this.txt_show.Text += "小王说:\n" + Convert.ToString(reader["content"]) + "\n";
                    }
                }
            }
        }
    }
    protected void Button1_Click(object sender, EventArgs e)
    {
         string sql = ConfigurationManager.ConnectionStrings["strcnn"].ConnectionString;
         using (SqlConnection sqlcnn = new SqlConnection(sql))
         {
             SqlCommand sqlcmm = sqlcnn.CreateCommand();
             sqlcmm.CommandText = "insert into chat ([content],createtime) values (@con,@time)";
             sqlcmm.Parameters.AddWithValue("@con",this.txt_say.Text.Trim ());
             sqlcmm.Parameters.AddWithValue("@time",DateTime.Now);
             sqlcnn.Open();
             sqlcmm.ExecuteNonQuery();
         }
         ScriptManager.RegisterStartupScript(this, this.GetType(), "", "<script>openLayer('test_con3')</script>", false);
        // this.txt_say.Text = "";
         this.txt_show.Text += "小王说:\n" + this.txt_say.Text + "\n";
    }
}