How to get query string parameter from MVC Razor markup?

Question

I want to check the URL parameter in my Razor markup. For example, how do I do something like this:

<div id="wrap" class="@{if (URL "IFRAME" PARAMETER EQUALS 1) iframe-page}">

Answer 1

Similar thread

<div id="wrap" class=' @(ViewContext.RouteData.Values["iframe"] == 1 ? /*do sth*/ : /*do sth else*/')> </div>

EDIT 01-10-2014: Since this question is so popular this answer has been improved.

The example above will only get the values from RouteData, so only from the querystrings which are caught by some registered route. To get the querystring value you have to get to the current HttpRequest. Fastest way is by calling (as TruMan pointed out) `Request.Querystring' so the answer should be:

<div id="wrap" class=' @(Request.QueryString["iframe"] == 1 ? /*do sth*/ : /*do sth else*/')> </div>

You can also check RouteValues vs QueryString MVC?

EDIT 03-05-2019: Above solution is working for .NET Framework.
As others pointed out if you would like to get query string value in .NET Core you have to use Query object from Context.Request path. So it would be:

<div id="wrap" class=' @(Context.Request.Query["iframe"] == new StringValues("1") ? /*do sth*/ : /*do sth else*/')> </div>

Please notice I am using StringValues("1") in the statement because Query returns StringValues struct instead of pure string. That's cleanes way for this scenerio which I've found.