[razor] How to add a second css class with a conditional value in razor MVC 4

While Microsoft has created some automagic rendering of html attributes in razor MVC4, it took me quite some time to find out how to render a second css class on an element, based on a conditional razor expression. I would like to share it with you.

Based on a model property @Model.Details, I want to show or hide a list item. If there are details, a div should be shown, otherwise, it should be hidden. Using jQuery, all I need to do is add a class show or hide, respectively. For other purposes, I also want to add another class, "details". So, my mark-up should be:

<div class="details show">[Details]</div> or <div class="details hide">[Details]</div>

Below, I show some failed attempts (resulting mark-up assuming there are no details).

This: <div @(@Model.Details.Count > 0 ? "class=details show" : "class=details hide")>,

will render this: <div class="details" hide="">.

This: <div @(@Model.Details.Count > 0 ? "class=\"details show\"" : "class=\"details hide\"")>.

will render this: <div class=""details" hide&quot;="">.

This: <div @(@Model.Details.Count > 0 ? "class='details show'" : "class='details hide'")>

will render this: <div class="'details" hide&#39;="">.

None of these are correct mark-up.

This:

    <div class="details @(Model.Details.Count > 0 ? "show" : "hide")">

will render this:

    <div class="details hide">

and is the mark-up I want.

You can use String.Format function to add second class based on condition:

<div class="@String.Format("details {0}", Details.Count > 0 ? "show" : "hide")">

You can add property to your model as follows:

    public string DetailsClass { get { return Details.Count > 0 ? "show" : "hide" } }

and then your view will be simpler and will contain no logic at all:

    <div class="details @Model.DetailsClass"/>

This will work even with many classes and will not render class if it is null:

    <div class="@Model.Class1 @Model.Class2"/>

with 2 not null properties will render:

    <div class="class1 class2"/>

if class1 is null

    <div class=" class2"/>