本文记录的是带领成员开发一个小模块功能的时候，需要用到弹出窗口加载树状级联单位选择，最后决定用采用jQuery+EasyUI插件进行开发。但是在使用EasyUI中tree的插件时，碰到了不少麻烦。为了提供弹出树的显示速度，就采用异步加载数节点值，首先先加载根节点，然后根据点击的节点展开加载子节点。

　　往往结果和预期的都不一样，困惑了几天，展开后子节点是动态加载了，但是收缩后无法清空之前填充的数据；第二次在展开时，子节点又被重复加载了一遍，造成了数据重复显示，并没有提供清除子节点的方法。想尽了各种办法来解决这个问题，只能换另一种形式加载子节点的值了，把每一个节点值保存起来，判断是否已经存在，存在就不在去加载。

　　两种方法见实例：

　　页面getTreeNode.ashx返回树节点JSON格式数据：

public class getTreeNode : IHttpHandler, System.Web.SessionState.IRequiresSessionState
{
    public void ProcessRequest(HttpContext context)
    {
        context.Response.ContentType = \"text/plain\";
        DataTable dt = (DataTable)context.Session[\"viewmaintain\"];
        string parentId = string.Empty;
        string resultStr = string.Empty;
        string attributes = string.Empty;
        string colName = string.Empty;
        string sql = string.Empty;
        string Casname = string.Empty;
        bool colt = false;
        string icon = \"icon-profile\";
        if (!string.IsNullOrEmpty(context.Request.QueryString[\"pid\"]))
        {
            parentId = context.Request.QueryString[\"pid\"].ToString();
        }
        if ((!string.IsNullOrEmpty(context.Request.QueryString[\"coln\"])) && (string.IsNullOrEmpty(context.Request.QueryString[\"casn\"])))
        {
            colName = HttpUtility.UrlDecode(context.Request.QueryString[\"coln\"].ToString());
            if (dt != null)
            {
                bool pt = true;
                while (pt)
                {
                    for (int i = 0; i < dt.Rows.Count; i++)
                    {
                        Casname = dt.Rows[i][\"view_colname\"].ToString();
                        if (dt.Rows[i][\"view_colname\"].ToString() == colName)
                        {
                            if (dt.Rows[i][\"view_cas\"].ToString() != null&&dt.Rows[i][\"view_cas\"].ToString() !=\"\")
                            {
                                colName = dt.Rows[i][\"view_cas\"].ToString();
                            }
                            else
                            {
                                colt = true;
                                sql = dt.Rows[i][\"view_sql\"].ToString();
                                pt = false;
                            }
                            break;
                        }
                    }
                }
            }
        }
        if ((!string.IsNullOrEmpty(context.Request.QueryString[\"casn\"])) && (!string.IsNullOrEmpty(context.Request.QueryString[\"coln\"])))
        {
           string casnName = HttpUtility.UrlDecode(context.Request.QueryString[\"casn\"].ToString());
           colName = HttpUtility.UrlDecode(context.Request.QueryString[\"coln\"].ToString());
            if (dt != null)
            {
                for (int i = 0; i < dt.Rows.Count; i++)
                {
                    Casname = dt.Rows[i][\"view_colname\"].ToString();
                    if (dt.Rows[i][\"view_cas\"].ToString() == casnName && casnName != colName)
                    {
                        colt = true;
                        sql = dt.Rows[i][\"view_sql\"].ToString();
                        break;
                    }
                }
            }
        }
        try
        {
            if (parentId != \"\" && colt == true)
            {
                //此处省略得到数据列表的代码
                List<TreeInfo> ltree = DAL_TreeInfo.GetItemValue(parentId, sql);
                resultStr = \"\";
                resultStr += \"[\";
                if (ltree.Count > 0)
                {
                    foreach (TreeInfo item in ltree)
                    {
                        attributes = \"\";
                        attributes += \"{\\\"cas\\\":\\\"\" + Casname;
                        attributes += \"\\\",\\\"val\\\":\\\"\" + item._text + \"\\\"}\";
                        resultStr += \"{\";
                        resultStr += string.Format(\"\\\"id\\\": \\\"{0}\\\", \\\"text\\\": \\\"{1}\\\", \\\"iconCls\\\": \\\"{2}\\\", \\\"attributes\\\": {3}, \\\"state\\\": \\\"closed\\\"\", item._id, item._text, icon, attributes);
                        resultStr += \"},\";
                    }
                    resultStr = resultStr.Substring(0, resultStr.Length - 1);
                }
                resultStr += \"]\";
            }
            else
            {
                resultStr = \"[]\";
            }
        }
        catch (Exception ex)
        {
            resultStr = \"出错\";
        }
        context.Response.Write(resultStr);
    }
    public bool IsReusable
    {
        get
        {
            return false;
        }
    }
}