What’s the difference between and ?

Pardon my ASP ignorance, but what’s the difference?

Answers:

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Method 1

These are somewhat informally referred to as “bee stings”. There are 4 types:

<%# %> is invoked during the DataBinding phase.

<%= %> is used to get values from code to the UI layer. Meant for backward compatibility with ASP applications. Shouldn’t use in .NET.

<%@ %> represents directives and allow behaviors to be set without resorting to code.

<%: %> (introduced in ASP.NET 4) is the same as %=, but with the added functionality of HtmlEncoding the output. The intention is for this to be the default usage (over %=) to help shield against script injection attacks.

Directives specify settings that are
used by the page and user-control
compilers when the compilers process
ASP.NET Web Forms pages (.aspx files)
and user control (.ascx) files.

ASP.NET treats any directive block
(<%@ %>) that does not contain an
explicit directive name as an @ Page
directive (for a page) or as an @
Control directive (for a user
control).

@Esteban – Added a msdn link to directives. If you need…more explanation, please let me know.

Method 2

See http://weblogs.asp.net/leftslipper/archive/2007/06/29/how-asp-net-databinding-deals-with-eval-and-bind-statements.aspx

As Albert says, it’s all to do with parsing databinding statements.

Method 3

The # version is used while data binding. <%= is just a simple Response.Write

Method 4

Not entirely related to the question, there’s another related notation in asp.net called Expression Builder:

<asp:SqlDataSource ... Runat="server"
 ConnectionString="<%$ ConnectionStrings:Northwind %>"
/>

<asp:Literal Runat="server"
  Text="<%$ Resources:MyResources, MyText %>"
/>

and it’s extensible, see http://msdn.microsoft.com/en-us/magazine/cc163849.aspx#S4

Method 5

javascript in .aspx that uses a master page.

var e = document.getElementById('<%= lblDescription.ClientID %>');
e.innerHTML = 'getElementById('lblDescription') will be null';

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