public virtual ListItem SelectedItem { get { int selectedIndex = this.SelectedIndex; if (selectedIndex >= 0) { return this.Items[selectedIndex]; } return null; }}public virtual string SelectedValue { get { int selectedIndex = this.SelectedIndex; if (selectedIndex >= 0) { return this.Items[selectedIndex].Value; } return string.Empty; }} 在没有选定任何项的情况下，SelectedValue默认值是string.Empty，而SelectedItem默认值是null（也就是说通过SelectedItem.Value可能发生异常）
1. selectedIndex——指的是dropdownlist中选项的索引，为int，从0开始，可读可写
2. selectedItem——指的是选中的dropdownlist中选项，为ListItem，只读不写
3. selectedValue——指的是选中的dropdownlist中选项的值，为string， 只读不写
4. selectedItem.Text——指的是选中的dropdownlist中选项的文本内容，与selectedItems的值一样为string，可读可写
5. selectedItem.value——指的是选中的dropdownlist中选项的值，与selectedValue的值一样，为string，可读可写
光看文字可能不太理解，我也是通过程序来加深理解的，下面举个例子：
前台代码：
代码 1 view plaincopy to clipboardprint? 2 <% @ Page Language = " C# " AutoEventWireup = " true " CodeFile = " dropdown.aspx.cs " Inherits = " dropdown " %> 3 4 <! DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd" > 5 6 < html xmlns ="http://www.w3.org/1999/xhtml" > 7 < head runat ="server" > 8 < title > 无标题页 </ title > 9 </ head > 10 < body > 11 < form id ="form1" runat ="server" > 12 < div > 13 < asp:DropDownList ID ="DropDownList1" runat ="server" > 14 < asp:ListItem Value ="1" > 北京 </ asp:ListItem > 15 < asp:ListItem Value ="2" > 上海 </ asp:ListItem > 16 < asp:ListItem Value ="3" > 广州 </ asp:ListItem > 17 </ asp:DropDownList > 18 < asp:Button ID ="Button1" runat ="server" OnClick ="Button1_Click" Text ="check" />< br /> 19 < asp:Label ID ="Label1" runat ="server" Text ="" ></ asp:Label > 20 < br /> 21 < asp:Label ID ="Label2" runat ="server" Text ="" ></ asp:Label > 22 < br /> 23 < asp:Label ID ="Label3" runat ="server" Text ="" ></ asp:Label >< br /> 24 < asp:Label ID ="Label4" runat ="server" Text ="" ></ asp:Label > 25 < br /> 26 < asp:Label ID ="Label5" runat ="server" Text ="" ></ asp:Label > 27 28 </ div > 29 </ form > 30 </ body > 31 </ html >
后台代码：
代码 1 using System; 2 using System.Data; 3 using System.Configuration; 4 using System.Collections; 5 using System.Web; 6 using System.Web.Security; 7 using System.Web.UI; 8 using System.Web.UI.WebControls; 9 using System.Web.UI.WebControls.WebParts; 10 using System.Web.UI.HtmlControls; 11 12 public partial class dropdown : System.Web.UI.Page 13 { 14 protected void Page_Load( object sender, EventArgs e) 15 { 16 17 } 18 protected void Button1_Click( object sender, EventArgs e) 19 { 20 Label1.Text = " selectedIndex= " + DropDownList1.SelectedIndex; 21 Label2.Text = " selectedItem= " + DropDownList1.SelectedItem; 22 Label3.Text = " selectedValue= " + DropDownList1.SelectedValue; 23 Label4.Text = " selectedItem.text= " + DropDownList1.SelectedItem.Text; 24 Label5.Text = " selectedItem.value= " + DropDownList1.SelectedItem.Value; 25 } 26 }
运行效果如下：
