在下拉框中显示树形菜单

    #region   在下拉框中显示树形菜单    private void BindDdlData(DropDownList ddl, int id)    {        DataSet ds = (DataSet)this.ViewState["ds"];        DataView dv = new DataView(ds.Tables[0]);        dv.RowFilter = "parentid = " + id.ToString();        int m = 0;        foreach (DataRowView drv in dv)        {            m++;            string blank = "";            if (id != 0)            {                for (int i = 0; i < m; i++)                {                    blank += "-";                }            }            ListItem li = new ListItem();            li.Text = blank + drv["categoryname"].ToString();            li.Value = drv["categoryid"].ToString();            ddl.Items.Add(li);            BindDdlData(ddl, Convert.ToInt32(drv["categoryid"]));        }    }    #endregion   在下拉框中显示树形菜单