asp.net: DropDownList绑定数据源及选中某个值的公用方法及例子

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using System.Web.UI.WebControls;
using System.Data;

namespace Common
{
    public abstract class DropDownListHelper
    {
        public readonly string STRING_VALUE = "STRING_VALUE";
        public readonly string STRING_TEXT = "STRING_TEXT";

        public static void SetSource(out string sError,DropDownList ddlCtrl, string sSQL,DataTable dtSource = null, bool bSelectFirstItem = false, string sFirstRowText = "")
        {
            sError = string.Empty;
            DataTable dt = null;

            try
            {
                if (!string.IsNullOrEmpty(sSQL))
                {
                    dt = SqlServerHelper.GetDataTable(out sError,sSQL);
                }
                else if (dtSource != null)
                {
                    dt = dtSource.Copy();
                }
            }
            catch (Exception ex)
            {
                sError = ex.Message.ToString();
                return;
            }

            ddlCtrl.Items.Clear();
            ddlCtrl.DataSource = null;

            if (dt != null && dt.Rows.Count > 0 && dt.Columns.Count > 1) // 一般为2列: id列 和 value 列
            {
                if (!string.IsNullOrEmpty(sFirstRowText))
                {
                    DataRow dr = dt.NewRow();
                    dr[dt.Columns[0]] = -1; // 这一项的 ID 值为 -1
                    dr[dt.Columns[1]] = sFirstRowText;
                    dt.Rows.InsertAt(dr, 0);// 从索引为0的位置插入
                }

                //ddlCtrl.AutoPostBack = true;
                ddlCtrl.DataSource = dt;
                ddlCtrl.DataValueField = dt.Columns[0].ColumnName; // 对应ID
                ddlCtrl.DataTextField = dt.Columns[1].ColumnName; // 显示内容
                ddlCtrl.DataBind();

                if (bSelectFirstItem) // 是否选中第一项
                {
                    int iID = 0;
                    if (Int32.TryParse(dt.Rows[0][0].ToString(), out iID))
                    {
                        ddlCtrl.SelectedValue = iID.ToString();
                    }
                }
                else
                {
                    ddlCtrl.Items.Insert(0, "");// 从索引为0的位置插入
                }
            }
        }

        public static void SelectItem(out string sError, DropDownList ddlCtrl, string sSQL,string sSelectedValue="")
        {
            sError = string.Empty;

            try
            {
                if (!string.IsNullOrEmpty(sSelectedValue)) ddlCtrl.SelectedValue = sSelectedValue;
                else if (!string.IsNullOrEmpty(sSQL))
                {
                    object oResult = SqlServerHelper.GetSingle(sSQL);
                    if (!Common.Tool.IsNullOrEmptyObject(oResult))
                        ddlCtrl.SelectedValue = oResult.ToString();
                }
            }
            catch (Exception ex)
            {
                sError = ex.Message.ToString();
                return;
            }

 
        }

    }
}

//绑定数据源方法:1
            string sError=string.Empty;
            Common.DropDownListHelper.SetSource(out sError, ddlAppName, "", 取下拉框数据源的dataTable,true,"无");
            if (!string.IsNullOrEmpty(sError)) { Common.MessageBox.Show(this, sError); return; }
//绑定数据源方法:2
            string sError=string.Empty;
            Common.DropDownListHelper.SetSource(out sError, ddlAppName, "取下拉框数据源的sql语句(2列就行了：id,value)", null,true,"无");
            if (!string.IsNullOrEmpty(sError)) { Common.MessageBox.Show(this, sError); return; }
//设置dropDownlist选中某个值
                    string sSQL = "select GroupID FROM sysUserGroup WHERE AppID= " + hidAppID.Value + " and UserID=" + hidUserID.Value;
                    Common.DropDownListHelper.SelectItem(out sError, ddlGroup, sSQL);
                    if (!string.IsNullOrEmpty(sError)) { Common.MessageBox.Show(this, sError); return; }
//Common.MessageBox.Show 方法：
		/// <summary>
		/// 显示消息提示对话框
		/// </summary>
		/// <param name="page">当前页面指针，一般为this</param>
		/// <param name="msg">提示信息</param>
		public static void  Show(System.Web.UI.Page page,string msg)
		{
            msg = msg.Replace("'", "\""); // 把单引号替换为双引号
            page.ClientScript.RegisterStartupScript(page.GetType(),"message", "<script language='javascript' defer>alert('" + msg.ToString() + "');</script>");
		}
// SqlServerHelper 类请参考：http://blog.csdn.net/keenweiwei/article/details/6845709