SharePoint list Search

using System;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using Microsoft.SharePoint;
using ASPWebPart = System.Web.UI.WebControls.WebParts;
using System.Xml;
using Microsoft.SharePoint.WebPartPages;
namespace Train.StudentQuery
{
    public partial class StudentQueryUserControl : UserControl
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!this.Page.IsPostBack)
            {
                SPSecurity.RunWithElevatedPrivileges(delegate()
                {
                    using (SPSite site = new SPSite(@"http://lwj:7004"))
                    {
                        using (SPWeb web = site.OpenWeb())
                        {
                            SPList list = web.Lists["班级信息"];
                            SPListItemCollection items = list.Items;
                            ddlClass.Items.Add(new ListItem("所有班级", ""));
                            foreach (SPListItem item in items)
                            {
                                string className = item["班级名称"] == null ? "" : item["班级名称"].ToString();
                                ddlClass.Items.Add(new ListItem(className, className));
                            }
                        }
                    }
                }); 
            }
        }

        protected void btnQuery_Click(object sender, EventArgs e)
        {
            string query = getQuery();
            execQuery(query);
        }
        protected void btnReset_Click(object sender, EventArgs e)
        {
            txtName.Text = "";
            for (int i = 0; i < ddlClass.Items.Count; i++)
            {
                ddlClass.Items[i].Selected = false;
            }
            ddlClass.Items[0].Selected = true;
            for (int i = 0; i < ddlSex.Items.Count; i++)
            {
                ddlSex.Items[i].Selected = false;
            }
            ddlSex.Items[0].Selected = true;
            string query = getQuery();
            execQuery(query);

        }
        /// <summary>
        /// 获取查询字符串
        /// </summary>
        /// <returns></returns>
        string getQuery()
        {

            string query = "";
            string addCaml = "";
            SPList list = SPContext.Current.Web.Lists["学员信息表"];
            if (this.txtName.Text != "")
            {
                addCaml = @"<Where>
                              <Contains>
                                 <FieldRef Name='" + list.Fields["姓名"].InternalName + @"' />
                                 <Value Type='Text'>" + txtName.Text + @"</Value>
                              </Contains>
                           </Where>";
                query = createCaml("And", query, addCaml);
            }
            if (this.ddlSex.SelectedItem.Value != "")
            {
                addCaml = @"<Where>
                              <Eq>
                                 <FieldRef Name='" + list.Fields["性别"].InternalName + @"' />
                                 <Value Type='Text'>" + this.ddlSex.SelectedItem.Value + @"</Value>
                              </Eq>
                           </Where>";
                query = createCaml("And", query, addCaml);
            }

            if (this.ddlClass.SelectedItem.Value != "")
            {
                addCaml = @"<Where>
                              <Eq>
                                 <FieldRef Name='" + list.Fields["所在班级"].InternalName + @"' />
                                 <Value Type='Text'>" + this.ddlClass.SelectedItem.Value + @"</Value>
                              </Eq>
                           </Where>";
                query = createCaml("And", query, addCaml);
            }
           //Response.Write("<script>alert('"+query+"')</script>");
            return query;
        }
        string createCaml(string logicType, string caml, string addCaml)
        {

            string returnCaml = "";
            if (caml == "")
            {
                XmlDocument meXml = new XmlDocument();
                meXml.LoadXml(addCaml);
                XmlNode mewhere = meXml.SelectSingleNode("Where");

                returnCaml = "<Where>"
                           + mewhere.InnerXml
                          + "</Where>";
            }
            else
            {

                XmlDocument docXml = new XmlDocument();
                docXml.LoadXml(caml);
                XmlNode where = docXml.SelectSingleNode("Where");
                XmlDocument meXml = new XmlDocument();

                meXml.LoadXml(addCaml);
                XmlNode mewhere = meXml.SelectSingleNode("Where");

                returnCaml = "<Where><" + logicType + ">" +
                           where.InnerXml +
                           mewhere.InnerXml +
                          "</" + logicType + "></Where>";
            }
            return returnCaml;

        }
        void execQuery(string query)
        {

            ASPWebPart.WebPartCollection webParts = ASPWebPart.WebPartManager.GetCurrentWebPartManager(this.Page).WebParts;
            foreach (ASPWebPart.WebPart wp in webParts)
            {
                if (wp is XsltListViewWebPart)
                {
                    XsltListViewWebPart xsltListViewWebPart = wp as XsltListViewWebPart;
                    if (xsltListViewWebPart != null)
                    {
                        string XmlDefinition = xsltListViewWebPart.XmlDefinition;
                        XmlDocument xmldoc = new XmlDocument();
                        xmldoc.LoadXml(XmlDefinition);
                        XmlNode ViewNode = xmldoc.SelectSingleNode("View");
                        ((XmlElement)ViewNode).SetAttribute("Scope", "Recursive");

                        XmlNode queryNode = xmldoc.SelectSingleNode("View/Query");
                        queryNode.InnerXml = query + queryNode.InnerXml;
                        XmlNode AggregationsNode = xmldoc.SelectSingleNode("View/Aggregations");
                        if (AggregationsNode == null)
                        {
                            XmlNode newAggregationsNode = xmldoc.CreateElement("Aggregations");
                            ((XmlElement)newAggregationsNode).SetAttribute("Value", "Off");
                            ViewNode.AppendChild(newAggregationsNode);
                        }
                        else
                        {
                            ((XmlElement)AggregationsNode).SetAttribute("Value", "Off");
                        }
                        //XmlNode ToolbarNode = xmldoc.SelectSingleNode("View/Toolbar");
                        //((XmlElement)AggregationsNode).SetAttribute("Type", "Freeform");
                        xsltListViewWebPart.XmlDefinition = xmldoc.OuterXml;
                        xsltListViewWebPart.AsyncRefresh = true;

                    }
                }
            }
        }
    }
}