<%$, <%@, <%=, <%# … w

问题:

I\'ve programmed in both classic ASP and ASP.NET, and I see different tags inside of the markup for server side code.

I\'ve recently come across a good blog on MSDN that goes over the difference between:

• <%= (percentage together with equals sign) and
• <%# (percent sign and hash/pound/octothorpe)

(<%# is evaluated only at databind, and <%= is evaluated at render), but I also see:

• <%$ (percent and dollar sign) and
• <%@ (percent sign and at symbol).

I believe <%@ loads things like assemblies and perhaps <%$ loads things from config files? I\'m not too sure.

I was just wondering if anyone could clarify all of this for me and possibly explain why it\'s important to create so many different tags that seemingly have a similar purpose?

回答1:

• <% %> - is for inline code (especially logic flow)
• <%$ %> - is for evaluating expressions (like resource variables)
• <%@ %> - is for Page directives, registering assemblies, importing namespaces, etc.
• <%= %> - is short-hand for Response.Write (discussed here)
• <%# %> - is used for data binding expressions.
• <%: %> - is short-hand for Response.Write(Server.HTMLEncode()) ASP.net 4.0+
• <%#: %> - is used for data binding expressions and is automatically HTMLEncoded.
• <%-- --%> - is for server-side comments

回答2:

You\'ve covered 2 of them (<%# is evaluated only at databind, and <%= is evaluated at render), and the answer for \"<%@\" is that it\'s compiler directives (ie., stuff like what you\'d put on a compiler\'s command line).

I don\'t know about \"<%$\".