Repeater ItemCommand事件未触发

我想当用户单击具有类session_box的Panel时，单击事件触发。但是当我点击它时，什么也没发生。当我调试代码时，ItemCommand事件甚至没有被调用!

下面是我的代码:

HTML:

<div id="sessions_wrapper">
    <asp:Repeater ID="sessions_repeater" runat="server" 
        DataSourceID="SqlDataSource1" 
        onitemcommand="sessions_repeater_ItemCommand">
        <ItemTemplate>
            <asp:Panel CssClass="session_box" runat="server" data-session-id='<%# Eval("session_id") %>'>
                <asp:Image CssClass="session_icon" runat="server" ImageUrl='<%# Eval("session_cover") %>' alt="" />
                <div class="session_info">
                    <p>Title: <%# Eval("session_name") %></p>
                    <p>Date: <%# Eval("session_date") %></p>
                    <p>Photos: <%# Eval("session_photos") %></p>
                </div>
            </asp:Panel>
        </ItemTemplate>
    </asp:Repeater>                            
    <asp:SqlDataSource ID="SqlDataSource1" runat="server" 
        ConnectionString="<%$ ConnectionStrings:DBCS %>" 
        ProviderName="<%$ ConnectionStrings:DBCS.ProviderName %>" 
        SelectCommand="SELECT * FROM [sessions]"></asp:SqlDataSource>
</div>

c#:

protected void sessions_repeater_ItemCommand(object source, RepeaterCommandEventArgs e)
{
    string sid = ((Panel)e.CommandSource).Attributes["data-session-id"];
    Response.Redirect("sessions.aspx?sid=" + sid);
}