[html] Conditional HTML Attributes using Razor MVC3

The variable strCSSClass often has a value but sometimes is empty.

I do not want to include an empty class="" in this input element's HTML, which means if strCSSClass is empty, I don't want the class= attribute at all.

The following is one way to do a conditional HTML attribute:

<input type="text" id="@strElementID" @(CSSClass.IsEmpty() ? "" : "class=" + strCSSClass) />

Is there a more elegant way of doing this? Specifically one where I could follow the same syntax as is used in the other parts of the element: class="@strCSSClass" ?

I guess a little more convenient and structured way is to use Html helper. In your view it can be look like:

@{
 var htmlAttr = new Dictionary<string, object>();
 htmlAttr.Add("id", strElementId);
 if (!CSSClass.IsEmpty())
 {
   htmlAttr.Add("class", strCSSClass);
 }
}

@* ... *@

@Html.TextBox("somename", "", htmlAttr)

If this way will be useful for you i recommend to define dictionary htmlAttr in your model so your view doesn't need any @{ } logic blocks (be more clear).

Note you can do something like this(at least in MVC3):

<td align="left" @(isOddRow ? "class=TopBorder" : "style=border:0px") >

What I believed was razor adding quotes was actually the browser. As Rism pointed out when testing with MVC 4(I haven't tested with MVC 3 but I assume behavior hasn't changed), this actually produces class=TopBorder but browsers are able to parse this fine. The HTML parsers are somewhat forgiving on missing attribute quotes, but this can break if you have spaces or certain characters.

<td align="left" class="TopBorder" >

OR

<td align="left" style="border:0px" >

What goes wrong with providing your own quotes

If you try to use some of the usual C# conventions for nested quotes, you'll end up with more quotes than you bargained for because Razor is trying to safely escape them. For example:

<button type="button" @(true ? "style=\"border:0px\"" : string.Empty)>

This should evaluate to <button type="button" style="border:0px"> but Razor escapes all output from C# and thus produces:

style="border:0px"

You will only see this if you view the response over the network. If you use an HTML inspector, often you are actually seeing the DOM, not the raw HTML. Browsers parse HTML into the DOM, and the after-parsing DOM representation already has some niceties applied. In this case the Browser sees there aren't quotes around the attribute value, adds them:

style=""border:0px""

But in the DOM inspector HTML character codes display properly so you actually see:

style=""border:0px""

In Chrome, if you right-click and select Edit HTML, it switch back so you can see those nasty HTML character codes, making it clear you have real outer quotes, and HTML encoded inner quotes.

So the problem with trying to do the quoting yourself is Razor escapes these.

If you want complete control of quotes

Use Html.Raw to prevent quote escaping:

<td @Html.Raw( someBoolean ? "rel='tooltip' data-container='.drillDown a'" : "" )>

Renders as:

<td rel='tooltip' title='Drilldown' data-container='.drillDown a'>

The above is perfectly safe because I'm not outputting any HTML from a variable. The only variable involved is the ternary condition. However, beware that this last technique might expose you to certain security problems if building strings from user supplied data. E.g. if you built an attribute from data fields that originated from user supplied data, use of Html.Raw means that string could contain a premature ending of the attribute and tag, then begin a script tag that does something on behalf of the currently logged in user(possibly different than the logged in user). Maybe you have a page with a list of all users pictures and you are setting a tooltip to be the username of each person, and one users named himself '/><script>$.post('changepassword.php?password=123')</script> and now any other user who views this page has their password instantly changed to a password that the malicious user knows.