DropDownList的使用

  protected void Page_Load(object sender, EventArgs e)
    {
        if(!IsPostBack)
        {
            //初始化数据
            List<ClassInfo> list = new List<ClassInfo>();
            ClassInfo cls1 = new ClassInfo { ClassId=1,ClassName="S1101"};
            ClassInfo cls2 = new ClassInfo { ClassId = 2, ClassName = "S2101" };
            ClassInfo cls3 = new ClassInfo { ClassId = 3, ClassName = "S2102" };
            ClassInfo cls4 = new ClassInfo { ClassId = 4, ClassName = "S3001" };

            list.Add(cls1);
            list.Add(cls2);
            list.Add(cls3);
            list.Add(cls4);


            //绑定数据源
            this.ddlClass.DataSource = list;
            this.ddlClass.DataTextField = "ClassName";
            this.ddlClass.DataValueField = "ClassId";

            this.ddlClass.DataBind();//如果不写，会如何？

            //插入友好提示
            this.ddlClass.Items.Insert(0, "请选择班级");

        }
    }
    protected void ddlClass_SelectedIndexChanged(object sender, EventArgs e)
    {
        this.lblMessage.Text = "选择的班级信息 ClassId: "+this.ddlClass.SelectedValue.ToString()
            + "  ClassName: " + this.ddlClass.SelectedItem.ToString(); ;
    }

页面层

 <form id="form1" runat="server">
    <div>
    
        班级：<asp:DropDownList ID="ddlClass" 
            runat="server" AutoPostBack="True" 
            onselectedindexchanged="ddlClass_SelectedIndexChanged">
        </asp:DropDownList>
        <br />
        <asp:Label ID="lblMessage" runat="server" Text=""></asp:Label>
    
    </div>
    </form>

实体层

public class ClassInfo
{
    public ClassInfo()
    {
        
    }
    public int ClassId { get; set; }
    public string ClassName { get; set; }
}

后台代码