通过递归方法 将DataTable中的树状数据信息 按树状格式显示在DropDownList中

DataTable中的数据：
TypeID , TypeName , ParentTypeID
1 类别A 0
2 类别B 0
3 子类别B1 2
4 子类别A1 1
5 孙类别A11 4

DropDownList的显示效果：
类别A
|--子类别A1
|----孙类别A11
类别B
|--子类别B1

Code
#region 绑定
private void fn_Bind_DropDownList()
{
DataSet ds;

//数据库操作 取出相应的ds
//ds = bll_Type.SelectAllTypeForChoose();

this.ddl_Type.Items.Clear();
if (ds != null && ds.Tables.Count > 0 && ds.Tables[0].Rows.Count > 0)
{
DataTable dtPara = ds.Tables[0];
DataTable dtTree = new DataTable();
dtTree = dtPara.Clone();
fn_ChangeToTree(ref dtTree, dtPara, 0, "0");//从顶级开始递归遍历

this.ddl_Type.DataSource = dtTree;
this.ddl_Type.DataTextField = dtTree.Columns[1].ToString();
this.ddl_Type.DataValueField = dtTree.Columns[0].ToString();
this.ddl_Type.DataBind();
}
this.ddl_Type.Items.Insert(0, new ListItem("", "0"));
}
#endregion

#region 将类别DataTable信息 整理成树状显示
private void fn_ChangeToTree(ref DataTable dtTree ,DataTable dtPara,int intLevel,string strParentTypeID)
{
intLevel++;
string strLeftPre = "";//处理每个级别的前缀内容显示
if(intLevel>1)
{
strLeftPre ="|" + strLeftPre.PadLeft(intLevel*2,'-');
}

DataTable dt1 = new DataTable();//当前类别
dt1 = dtPara.Clone();
DataTable dt2 = new DataTable();//下一级
dt2 = dtPara.Clone();

for (int i = 0; i < dtPara.Rows.Count; i++)
{
DataRow dr = dtPara.Rows[i];
string strRowParentTypeID = dr["ParentTypeID"].ToString();
if (strRowParentTypeID == strParentTypeID)
{
dt1.Rows.Add(dr.ItemArray);
}
else
{
dt2.Rows.Add(dr.ItemArray);
}
}

for (int j = 0; j < dt1.Rows.Count; j++)
{
DataRow dr = dt1.Rows[j];

dr["TypeName"] = strLeftPre + dr["TypeName"].ToString();
dtTree.Rows.Add(dr.ItemArray);
string strRowParentTypeID = dr["TypeID"].ToString();
fn_ChangeToTree(ref dtTree, dt2, intLevel, strRowParentTypeID);//递归
}
}
#endregion