Asp.net中慎用Page.DataBind()

问题代码

Default.aspx:

<asp:DropDownList ID="ddlTradingServiceType" CssClass="s_w90 m-r0" runat="server"
        EnableViewState="false">
        <asp:ListItem Value="-1">全部</asp:ListItem>
        <asp:ListItem Value="consignment">寄售交易</asp:ListItem>
        <asp:ListItem Value="escort">担保交易</asp:ListItem>
        <asp:ListItem Value="id">帐号交易</asp:ListItem>
        <asp:ListItem Value="api">官方合作交易</asp:ListItem>
        <asp:ListItem Value="cardservice">点卡交易</asp:ListItem>
    </asp:DropDownList><a href="?ts=nodefine">跳跳</a>

 

Default.aspx.cs:

protected void Page_Load(object sender, EventArgs e)
        {
            if (!string.IsNullOrEmpty(Request.QueryString["ts"]))
            {
                ddlTradingServiceType.SelectedValue = Request.QueryString["ts"];
                ddlTradingServiceType.DataBind();
            }
        }

 

当页面点击"跳跳"时，页面会报错

原因在我给dllTradingServiceType.SelectedValue赋值后，调用了DataBind()，而在控件数据绑定的时候，服务会发现dllTradingServiceType的Items集合中没有Value为nodefine的项，故报无效SelectedValue的错误。往往在写程序时我们会给DropDownList控件的SelectedValue赋值一个不存在的Value，如果我们不调用DataBind()，服务器是不会检测项目列表的，故不会出错，事实上这种写法存在问题。MSDN对Page.DataBind()的解释：
Binds a data source to the invoked server control and all its child controls.

Remarks
Use this method to bind data from a source to a server control. This method is commonly used after retrieving a data set through a database query.

Note   When called on a server control, this method resolves all data-binding expressions in the server control and in any of its child controls.

This method is commonly overridden when creating custom templated data-bound controls. For more information, see Developing a Templated Data-Bound Control.

For more information about data binding to server controls, see Data Binding Expression Syntax.