【ASP.net控件】DropDownList数据绑定一个小bug

浏览数：18 / 时间：2015年06月09日

　　绑定数据出现这种情况，明明在第一项插入了一条数据，却始终在DropDownList中没有显示出来。

　代码如下：　

if (!IsPostBack)
            {

                //绑定城市
                DataTable dtCity = new HighSearch().GetCitySelect();
                DropDownList1.DataSource = dtCity;
                DropDownList1.DataValueField = "citycode";
                DropDownList1.DataTextField = "cityname";
                DataBind();
                DropDownList1.Items.Insert(0, new ListItem("请选择城市", ""));
                DropDownList2.Items.Insert(0, new ListItem("请选择线路", ""));
                DropDownList3.Items.Insert(0, new ListItem("请选择站点", ""));

                //绑定项目
                DataTable dtProject = new HighSearch().GetProjectSelect();
                DropDownList4.DataSource = dtProject;
                DropDownList4.DataValueField = "projectname";
                DropDownList4.DataTextField = "projectname";
                DataBind();
                DropDownList4.Items.Insert(0, new ListItem("请选择项目", ""));

            }

结果如下：

找了好久才找到原因，原因是DropDownList要先绑定完数据后再插入选项。

修改代码如下：

if (!IsPostBack)
            {            
                //绑定项目
                DataTable dtProject = new HighSearch().GetProjectSelect();
                DropDownList4.DataSource = dtProject;
                DropDownList4.DataValueField = "projectname";
                DropDownList4.DataTextField = "projectname";
                DataBind();
         
                //绑定城市
                DataTable dtCity = new HighSearch().GetCitySelect();
                DropDownList1.DataSource = dtCity;
                DropDownList1.DataValueField = "citycode";
                DropDownList1.DataTextField = "cityname";
                DataBind();

                DropDownList1.Items.Insert(0, new ListItem("请选择城市", ""));
                DropDownList2.Items.Insert(0, new ListItem("请选择线路", ""));
                DropDownList3.Items.Insert(0, new ListItem("请选择站点", ""));
                DropDownList4.Items.Insert(0, new ListItem("请选择项目", ""));
                            
            }