Why can not use <%=...%> in the ListView - asp.net

Question

All, Generally .If we want to output a variable in a page which defined in the code-behind class file of page . We could set the variable with public or protect visibility. and in the front page we can use it like below.
<%=VariableName%>.
But I don't know why can't use it in the ListView. Please help to review my code.
In the front page
<div id="divIssuedListContainer" class="myIssuedList">
<asp:ListView id="listShower" runat="server">
<LayoutTemplate>
<div id="divIssuedListHeadTitle">
<div id="divIssuedListTitleIco">
<img alt="" src="ico/IssuedCap.png" />
</div>
<div id="divIssuedListTitleName">
<span>ISSUED</span><span>TRADE NAMES</span><span>/LICENSES</span>
</div>
<div id="divIssuedListItemNumber">
<span>
<%=iListNumber%></span>
</div>
</div>
<div style="clear:both"></div>
<div id="divIssuedListBody">
<ul>
<asp:PlaceHolder runat="server" ID="itemPlaceholder"></asp:PlaceHolder>
</ul>
</div>
</LayoutTemplate>
<ItemTemplate>
<li>
<table>
<tr>
<td>
<img alt="" src="" />
</td>
<td>
<div>
<span>
<%# Eval("altID") %>
-
<%# Eval("englishTradeName") %></span></div>
<div>
<span>Expired Date:<%# Eval("expDate") %></span>
</div>
</td>
</tr>
</table>
</li>
</ItemTemplate>
</asp:ListView>
In the code-behind of page
public partial class _Default : System.Web.UI.Page
{
protected int iListNumber = 0;
protected void Page_Load(object sender, EventArgs e)
{
List<SimpleCapModel> DataSourceList = TestDataHelper.GetMyIssuedList();
listShower.DataSource = DataSourceList;
iListNumber = DataSourceList.Count();
listShower.DataBind();
}
}
I got an error page said :
The Controls collection cannot be modified because the control contains code blocks (i.e. <% ... %>).
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
Exception Details: System.Web.HttpException: The Controls collection cannot be modified because the control contains code blocks (i.e. <% ... %>).
Source Error:
Line 19: listShower.DataSource = DataSourceList;
Line 20: iListNumber = DataSourceList.Count();
Line 21: listShower.DataBind();//this line cause error.
Line 22: }
Line 23: }
And If I use the expression <%#iListNumber%>. The error is gone, but I got a empty value instead of the number of the list. please review below rendered result html :
<div id="divIssuedListItemNumber">
<span> </span>
</div>
I didn't know whether I missed something ? If I did .Please help to let me know it.thanks.

Answer 1

You need to use <%#iListNumber %> because you are using data-binding the ListView, otherwise you'll get the exception (see: http://support.microsoft.com/kb/976112 for more on inline expressions).
Try using <%#iListNumber.ToString %> and see if that makes a difference.
UPDATE:
The problem appears to be that your inline-expression is in the LayoutTemplate, where data-binding [apparently] won't work without either handling the OnLayoutCreated event, or extending the ListView.
See either of the following for examples of how to extend the ListView:
http://www.codeproject.com/Articles/42962/Databind-Expression-in-ListView-LayoutTemplate
http://forums.asp.net/p/1201992/3319344.aspx#3319344

Answer 2

Given the error you're receiving, it basically means this: you can't just randomly throw .NET tags in databound controls.
The solution is to, instead, throw that random text in a .NET control, like this: <asp:Literal Runat="server" Text="<%# iListNumber %>" />
When you put a .NET codeblock in code, it dynamically has to build a control placeholder for it. It's a little tricky. But if you wrap all your custom tags up in a control, then just that one property gets databound and the databound block remains "clean" if that makes sense.