下拉列表问题

Question

 protected void btnSearch_Click(object sender, EventArgs e)
        {
            if (this.ProList.SelectedIndex<0)
                this.label.Text = "请选择部门！";
            else
                DoSearch();
        }
我是这么写的,但是有错误,说序列不包含任何元素 
下拉列表 :    ------请选择--------
                     部门1
                     部门2
                     部门3

Answer 1

 protected void btnSearch_Click(object sender, EventArgs e)
        {
            if (this.ProList.SelectedIndex<0)
                this.label.Text = "请选择部门！";
            else
                DoSearch();
        }
我是这么写的,但是有错误,说序列不包含任何元素 
下拉列表 :    ------请选择--------
                     部门1
                     部门2
                     部门3

Answer 2

protected void btnSearch_Click(object sender, EventArgs e)
        {
            if (this.ProList.SelectedIndex<0)
                this.label.Text = "请选择部门！";
            else
                DoSearch();
        }
我是这么写的,但是有错误,说序列不包含任何元素 
下拉列表 :    ------请选择--------
                     部门1
                     部门2
                     部门3

Answer 3

在page_load里
if(!postback)
中
重新绑定数据源
你现在的问题是,一刷新,dropdownlist就被清空了

Answer 4

回调的时候先走一边pageload，你确定你的dropdownlist绑定数据源是在！ispostback里边绑的？

Answer 5

 #region 初始化页面
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                InitDropDownList();
                if (Request.QueryString.Count == 1)
                {
                    string Year = Request.QueryString["Year"];
                    this.ddlYear.SelectedValue = Year;
                    DoSearch();
                }
            }
        }
        #endregion private void InitDropDownList()
        {
            var yearMax = (from my in eipc.ManHours
                           select my.DateTime.Value.Year).Max();
            var yearMin = (from my in eipc.ManHours
                           select my.DateTime.Value.Year).Min();
            this.ddlYear.Items.Clear();
            for (int i = yearMin; i <= yearMax; i++)
            {
                ListItem lItem = new ListItem();
                lItem.Text = i.ToString();
                lItem.Value = i.ToString();
                this.ddlYear.Items.Add(lItem);
            }
            this.ddlYear.SelectedValue = yearMax.ToString();            var query = from a in eipc.Departments
                        where a.DeptNo != "T0001" 
                        orderby a.StruDeptNo
                        select new
                        {
                            a.DeptNo,
                            a.CnName
                        };            ProList.DataSource = query;
            ProList.DataTextField = "CnName";
            ProList.DataValueField = "DeptNo";
            ProList.DataBind();
            this.ProList.Items.Insert(0, new ListItem("请选择部门", "0"));        }

Answer 6

把 SelectedIndex<0 改成 SelectedIndex==0就可以了