DropDownList分层显示！

public static void BindDropFatherItem( DropDownList DropDownList )
    {
        DropDownList.Items.Clear();
        string strSql = "select * from Department";
        DataTable dt = DB.GetTable( strSql );//获取所有节点

        //判断跟节点数量
        string strSql1 = "select count(*) from Department where  ParentID = 0";
        int ParentCount = Convert.ToInt32( DB.ExecuteScalar( strSql1 ) );

        if( dt.Rows.Count > 0 )
        {
            foreach( DataRow dr in dt.Rows )
            {
                if( ParentCount == 0 )
                {
                    if( dr[ "ParentID" ].ToString().Trim() == "0" )//绑定根节点   
                    {
                        DropDownList.Items.Insert( 0, "请选择" );
                        DropDownList.Items.Add( new ListItem( dr[ "DepName" ].ToString(), dr[ "DepID" ].ToString() ) );
                        BindDropChildItem( DropDownList, dt, dr[ "DepID" ].ToString(), 1 );
                    }
                }
                else
                {
                    if( dr[ "ParentID" ].ToString().Trim() == "0" )//绑定根节点   
                    {                        
                        DropDownList.Items.Add( new ListItem( dr[ "DepName" ].ToString(), dr[ "DepID" ].ToString() ) );
                        BindDropChildItem( DropDownList, dt, dr[ "DepID" ].ToString(), 1 );
                    }
                }
                
            }
        }
    }

public static void BindDropChildItem( DropDownList DropDownList, DataTable dt, string id, int length )
    {
        DataRow[] rows = dt.Select( "ParentID='" + id + "'", "DepID  ASC" );//取出id子节点进行绑定   
        for( int i = 0; i < rows.Length; i++ )
        {
            DropDownList.Items.Add( new ListItem( Department.SpaceLength( length ) + rows[ i ][ "DepName" ].ToString(), rows[ i ][ "DepID" ].ToString() ) );
            BindDropChildItem( DropDownList, dt, rows[ i ][ "DepID" ].ToString(), length + 1 );//空白数目加1   
        }
    }

    //   子节点前面的空白数 
    public static string SpaceLength( int i )
    {
        string space = "";
        for( int j = 0; j < i; j++ )
        {
            space += "------";//分层显示字符；   
        }
        return space;
    }