asp.net使用DataGridTree实现下拉树的方法

        {
            _dropdowntree = dropdowntree;
        }
        /**//// <summary>
        /// 用于树的前缀
        /// </summary>
        /// <param name="islast">是否是同级节点中的最后一个</param>
        /// <param name="haschild">本节点是否拥有子节点</param>
        /// <param name="parentstring">父节点前缀符号</param>
        /// <returns>本节点的前缀</returns>
        private string getprefix(bool islast, bool haschild, string parentstring)
        {
            string result = string.empty;
            if (!string.isnullorempty(parentstring))
            {
                parentstring = parentstring.remove(parentstring.length - 1).replace("├", "│").replace("└", "　");
                result += parentstring;
            }
            if (islast)
            {
                result += "└";
            }
            else
            {
                result += "├";
            }
            if (haschild)
            {
                result += "┬";
            }
            else
            {
                result += "─";