ASP.net技术：AJAX实现留言板信息展开

实例说明
留言板是目前网络比较流行的、方便的、快捷的一种用来保存留言的网络工具。用户可以通过留言板为网站管理人员留言，也可以作为用户与管理员交流的通信工具。留言板通常应用在企业门户网站、电子商务销售平台网等网站。

技术要点
DynamicPopulate控件提供了一种动态效果，能通过WebService或访问服务器端代码获取一段HTML文本，并替换掉目标控件上原来的内容。DynamicPopulate控件的主要属性及说明如表所示
表 DynamicPopulate控件的属性及说明

实现过程
（1）新建一个AJAX网站，命名为07，默认窗体为Default.aspx。

（2）在Default.aspx窗体中主要添加一个ScriptManager控件、一个UpdatePanel控件和一个GridView控件，分别用于管理页面中的AJAX控件、实现局部更新、显示留言板信息。

（3）对GridView控件进行编辑列，添加一个TemplateField项。

（4）编辑GridView模板，在模板中设计代码如下：

 <ItemTemplate>
           <table style="height: 1px" width="100%" cellpadding="0" cellspacing="0">
              <tr>
                   <td colspan="3">
              <hr />
                     &nbsp;</td>
                               </tr>
                                 <tr>
                                    <td width="80">
                                                留言标题：</td>
                                            <td colspan="2">
                                                <%# Eval("title") %>
                                            </td>
                                        </tr>
                                        <tr>
                                            <td style="vertical-align: top; height: 11px" width="80">
                                                留言内容：</td>
                                            <td colspan="2" style="height: 11px; vertical-align: top;">
                                                <%# Eval("message") %>
                                            </td>
                                        </tr>
                                        <tr>
                                            <td style="height: 26px;" width="80">
                                            </td>
                                            <td colspan="2" style="height: 26px">
                                                <table cellpadding="0" cellspacing="0" width="100%">
                                                    <tr>
         <td colspan="3" style="height: 17px" align="right">
                 < a href="#message">我要留言</a> <a href='Reply.aspx?MessageID= <%# Eval("ID") %>'>我要回复</a>
         <asp:HyperLink ID="hlnkShow" runat="server" NavigateUrl="#">展开>></asp:HyperLink>&nbsp;
                  </td>
                                                    </tr>
                                                    <tr>
          <td colspan="3">
           <asp:Panel ID="plReturn" runat="server" Height="0px" Width="100%">
                                                            </asp:Panel>
                                                        </td>
                                                    </tr>
                                                    <tr>
          <td colspan="3">
       <cc1:DynamicPopulateExtender ID="dpeReturn" runat="server" ServicePath="Return.asmx"
           ServiceMethod="GetReplyByMessage" ContextKey='<%# Eval("ID") %>' ClearContentsDuringUpdate="true"
                        PopulateTriggerControlID="hlnkShow" TargetControlID="plReturn">
        </cc1:DynamicPopulateExtender>
                                                        </td>
                                                    </tr>
                                                </table>
                                            </td>
                                        </tr>
                                        <tr>
                                            <td width="80">
                                            </td>
                                            <td colspan="2">
                                                <table style="width: 512px">
                                                    <tr>
                                               <td style="width: 103px">
                                                   留言人联系方式：</td>
                                              <td style="width: 214px">
                                              <a href='mailto:<%# Eval("Email") %>'>
                                                     <%# Eval("Email") %>
                                                  </td>
                                              <td style="width: 41px">
                                            时间：</td>
                                        <td>
                                   [<%# Eval("CreateDate") %>]
                               </td>
                       </tr>
                   </table>
                 </td>
           </tr>
        /table>
   </ItemTemplate>

（5）创建一个Web服务，命名为Return.asmx。在WEB服务中创建GetReplyByMessage方法来实现留言板中的信息展开。代码如下：

[WebMethod]
    public string GetReplyByMessage(string contextKey)
    {
        OleDbConnection conn = new OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + Server.MapPath("Ex18_07.mdb"));
        OleDbDataAdapter da = new OleDbDataAdapter("select * from tb_reply  where messageID = " + contextKey + " Order by CreateDate DESC", conn);
        DataSet ds = new DataSet();
        da.Fill(ds);

        if (ds == null || ds.Tables.Count <= 0 || ds.Tables[0].Rows.Count <= 0)
        {
            return string.Empty;
        }
        StringBuilder returnHtml = new StringBuilder();
        foreach (DataRow row in ds.Tables[0].Rows)
        {
            returnHtml.Append("<tabel><tr><td>回复" + row["CreateDate"]);
            returnHtml.Append("</td><br /><br /><td>");
            returnHtml.Append(row["Reply"]);
            returnHtml.Append("</td></tr><br /><br /></tabel>");
        }
        return returnHtml.ToString();
    }

（6）在Default.aspx.cs文件获取数据库中的留言信息，实现代码如下：

protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            OleDbConnection conn = new OleDbConnection(@"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + Server.MapPath("Ex18_07.mdb"));
            OleDbDataAdapter da = new OleDbDataAdapter("select * from tb_Message  Order by CreateDate DESC", conn);
            DataSet ds = new DataSet();
            da.Fill(ds);
            GridView1.DataSource = ds;
            GridView1.DataBind();
        }
    }