Neat way to conditionally test whether to add a class in HAML template [duplicate]

问题

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Closed 7 years ago.

Possible Duplicate:
Append class if condition is true in Haml (with Rails)

I'm using a template that allows you to mark a list item as current (using class=current), highlighting it in a nav bar.

In HAML, this looks like:

%li.current
  Menu item A
%li
  Menu item B
%li
  Menu item C

I have this code in a Sinatra view and want to programmatically add the class=current, depending on a parameter to the view.

How do I do this in the neatest way possible?

Currently, I'm doing it like this:

  - if section == "pages"
    %li.current
      %a{:href => "#pages"} Pages
  - else
    %li
      %a{:href => "#pages"} Pages

Which feels too verbose.

回答1:

You can inline the conditional to determine if the class is needed for the %li

%li{ :class => ('current' if section == "pages") }
  %a{ :href => "#pages" } Pages

回答2:

If section can be another string rather than "pages", you should use something like mguymon answered. But if it can only be nil, false or "pages" this code is more succinct:

%li{ class:section && 'current' }
  %a{ :href => "#pages" } Pages

This use the principle that HAML omit nil or false attributes and every object in Ruby is evalueted as true, except: false and nil.

So, if section is different than nil or false, then section && 'current' outputs 'current' else it outputs false omitting the class attribute.

来源：https://stackoverflow.com/questions/12312052/neat-way-to-conditionally-test-whether-to-add-a-class-in-haml-template