What is the difference between <%#%> and <%=%>?
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Answer Posted / vinodh reddy
I was a little confused about the difference between <%=
expression %> and <%# expression %> in ASP.NET. It seems
like both work in a lot of cases, but in other cases, only
the # (data binding) version works. So, I decided to dig
into it a little bit. To try it out I built this simple
page:
<%@ Page Language="C#" AutoEventWireup="true"
CodeFile="Default.aspx.cs" Inherits="_Default" %><!DOCTYPE
html PUBLIC "-//W3C//DTD XHTML 1.0
Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-
transitional.dtd"><html
xmlns="http://www.w3.org/1999/xhtml" ><head
runat="server"> <title>Untitled
Page</title></head><body> <form id="form1"
runat="server"> <div> <p>Equals: <%=
this.TestValue %></p> <p>Pound: <%# this.TestValue %
></p> <p>Equals label: <asp:Label runat="server"
ID="_equals" Text="<%= this.TestValue %>" /></p>
<p>Pound label: <asp:Label runat="server" ID="_pound"
Text="<%# this.TestValue %>" /></p> </div>
</form></body></html>
And the code behind is:
public partial class _Default : System.Web.UI.Page {
protected void Page_Load(object sender, EventArgs e)
{ _testValue = "2"; } protected void
Page_PreRenderComplete(object sender, EventArgs e)
{ // DataBind(); _testValue = "3"; }
public string TestValue { get { return
_testValue; } } private string _testValue = "1";}
Here's what the result is when the DataBind() line is
commented out:
Equals: 3
Pound:
Equals label:
Pound label:
And, when it's not commented out:
Equals: 3
Pound: 2
Equals label:
Pound label: 2
At first glance it looks like the Equals label case did
nothing. But, if you view source, you see:
<p>Equals label: <span id="_equals"><%= this.TestValue %
></span></p>
The literal expression made it down to the browser and it's
just invalid HTML. What you can see as a result is:
The <%= expressions are evaluated at render time
The <%# expressions are evaluated at DataBind() time and
are not evaluated at all if DataBind() is not called.
<%# expressions can be used as properties in server-side
controls. <%= expressions cannot.
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