In today’s post I’m going to discuss a small, but useful,
feature we’ve recently introduced: server-side comment support in Razor.
Why Server Side Comments?
Scenario: You are working within a view template, and want
to temporarily disable some content or view code (potentially to help track
down a problem, or to temporarily change the output of your site).
HTML supports client-side comments (<!-- -->), which
you can use to prevent a browser from parsing/running/displaying the HTML
content within it. The problem with using this approach for many
scenarios, though, is that the content contained within the comment is still
sent down from the server to the client unnecessarily – and the server-side
code within the comment will still execute on the server.
ASP.NET Web Forms supports a server-side comment syntax (<%-- --%>) that you can
use to completely disable content/code/controls within a page. With
server-side comments, the ASP.NET Web Forms compiler completely ignore
everything within the <%-- --%> blocks at parse time, and removes the content
completely when assembling the page (like the contents wasn’t there at
all). You can learn more about this feature from an older blog post of
mine here.
One question someone asked me earlier this week was “is
there an equivalent way to do this with Razor?”. The answer is - yes!
Server Side Comments with Razor
Razor now allows you to wrap any code/content/region of a
view within a @* comment *@ syntax (which works for both C# and VB
templates). This syntax indicates that the Razor parser should ignore
everything within that block and treat it like it isn’t there at all (meaning
nothing is ever executed, there is no performance overhead at runtime, and
nothing is sent down to the client).
For example, below I’ve wrapped some HTML content and
server-code within a @* *@ block. This is equivalent to it not being
there at all:
Notice above how Visual Studio (starting with
this week’s ASP.NET MVC 3 RC build) now colorizes comments (by default in
green) to make them more visible within the editor.
Visual Studio also now enables you to use the
comment/uncomment buttons on the text editor toolbar to easily comment/un-comment
a block of text/code. For example, we could select the above @* *@
comment block within the text editor, and then click the “Uncomment” toolbar
button (or better yet press Ctrl+K, Ctrl+U) to have VS uncomment the region:
When we do this the editor will automatically
uncomment the block for us (saving us some keystrokes):
We could then highlight another region of text/code within
the editor, and then either click the “Comment” toolbar button or press Ctrl+K,
Ctrl+C to apply a server-side comment
When we do this the editor will automatically
comment the block for us (saving us some keystrokes):
