新人求解:必须在 ListView“Listview1”上指定项占位符。可通过将控件的 ID 的属性设置为“itemPlaceholder”来指定项占位符


        protected void Page_Load(object sender, EventArgs e)
        {
            DataSet ds = XXXXXXX; //能得到dataset
            Listview1.DataSource = ds.Tables[0].DefaultView;
            Listview1.DataBind();        
        } <asp:listview ID="Listview1" runat="server">
        <LayoutTemplate>
            <table runat="server">
                <tr runat="server" style="background-color: #98FB98">
                    <th runat="server">id</th>
                    <th runat="server">year</th>
                    <th runat="server">title</th>
                    <th runat="server">conditions</th>
                </tr>
                <tr runat="server" id="itemPlachHoder"></tr>            </table>
        </LayoutTemplate>
        <ItemTemplate>
            <tr runat="server">
                <td><asp:Label runat="server" ID="lb_id" Text='<%#Eval("ID") %>'></asp:Label></td>
                <td><asp:Label runat="server" ID="lb_year" Text='<%#Eval("GRAYEAR") %>'></asp:Label></td>
                <td><asp:Label runat="server" ID="lb_title" Text='<%#Eval("TITLE") %>'></asp:Label></td>
                <td><asp:Label runat="server" ID="lb_condition" Text='<%#Eval("CONDITIONS") %>'></asp:Label></td>
            </tr>
        </ItemTemplate>
    </asp:listview>
为什么还会报错
须在 ListView“Listview1”上指定项占位符。可通过将控件的 ID 的属性设置为“itemPlaceholder”来指定项占位符。项占位符控件还必须指定 runat="server"。 
呢？