Ruby-on-rails Rails 检查 yield :area 是否在 content_for 中定义
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Rails check if yield :area is defined in content_for
提问by William Yeung
I want to do a conditional rendering at the layout level based on the actual template has defined content_for(:an__area), any idea how to get this done?
我想根据已定义的实际模板在布局级别进行条件渲染content_for(:an__area)，知道如何完成此操作吗？
回答by gudleik
@content_for_whateveris deprecated.
Use content_for?instead, like this:
@content_for_whatever已弃用。content_for?改为使用，如下所示：
<% if content_for?(:whatever) %>
<div><%= yield(:whatever) %></div>
<% end %>
回答by efalcao
not really necessary to create a helper method:
创建辅助方法并不是真正必要的：
<% if @content_for_sidebar %>
<div id="sidebar">
<%= yield :sidebar %>
</div>
<% end %>
then of course in your view:
那么当然在你看来：
<% content_for :sidebar do %>
...
<% end %>
I use this all the time to conditionally go between a one column and two column layout
我一直使用它来有条件地在一列和两列布局之间切换
回答by gregwinn
<%if content_for?(:content)%>
<%= yield(:content) %>
<%end%>
回答by Nick
Can create a helper:
可以创建一个助手：
def content_defined?(var)
content_var_name="@content_for_#{var}"
!instance_variable_get(content_var_name).nil?
end
And use this in your layout:
并在您的布局中使用它：
<% if content_defined?(:an__area) %>
<h1>An area is defined: <%= yield :an__area %></h1>
<% end %>
回答by Enrico
I'm not sure of the performance implications of calling yield twice, but this will do regardless of the internal implementation of yield (@content_for_xyz is deprecated) and without any extra code or helper methods:
我不确定两次调用 yield 对性能的影响，但是无论 yield 的内部实现如何（@content_for_xyz 已弃用）并且没有任何额外的代码或辅助方法，这都将起作用：
<% if yield :sidebar %>
<div id="sidebar">
<%= yield :sidebar %>
</div>
<% end %>
回答by William Yeung
Ok I am going to shamelessly do a self reply as no one has answered and I have already found the answer :) Define this as a helper method either in application_helper.rb or anywhere you found convenient.
好的，我将无耻地做一个自我回复，因为没有人回答，我已经找到了答案:) 在 application_helper.rb 或任何您觉得方便的地方将其定义为辅助方法。
def content_defined?(symbol)
content_var_name="@content_for_" +
if symbol.kind_of? Symbol
symbol.to_s
elsif symbol.kind_of? String
symbol
else
raise "Parameter symbol must be string or symbol"
end
!instance_variable_get(content_var_name).nil?
end
