rails中 yeild 与 content_for之间的区别

yield is how you specify where your content areas is going to go within a layout. You might have something like this:

yield 是你指明您的内容将如何放在一个布局中。你可能会有这样的事情：

<code style="margin:0px; padding:0px; border:0px; vertical-align:baseline; font-family:Consolas,Menlo,Monaco,'Lucida Console','Liberation Mono','DejaVu Sans Mono','Bitstream Vera Sans Mono','Courier New',monospace,serif; white-space:inherit"><span class="tag" style="color:#8000;margin:0px; padding:0px; border:0px; vertical-align:baseline; background-color:transparent;"><div></span><span class="pln" style="margin:0px; padding:0px; border:0px; vertical-align:baseline; background-color:transparent">  </span><span class="tag" style="color:#8000;margin:0px; padding:0px; border:0px; vertical-align:baseline; background-color:transparent;"><h1></span><span class="pln" style="margin:0px; padding:0px; border:0px; vertical-align:baseline; background-color:transparent"> This is the wrapper!</span><span class="tag" style="color:#8000;margin:0px; padding:0px; border:0px; vertical-align:baseline; background-color:transparent;"></h1></span><span class="pln" style="margin:0px; padding:0px; border:0px; vertical-align:baseline; background-color:transparent">  </span><span class="pun" style="margin:0px; padding:0px; border:0px; vertical-align:baseline; background-color:transparent"><%=</span><span class="pln" style="margin:0px; padding:0px; border:0px; vertical-align:baseline; background-color:transparent"> </span><span class="kwd" style="color:#008b;margin:0px; padding:0px; border:0px; vertical-align:baseline; background-color:transparent;">yield</span><span class="pln" style="margin:0px; padding:0px; border:0px; vertical-align:baseline; background-color:transparent"> </span><span class="pun" style="margin:0px; padding:0px; border:0px; vertical-align:baseline; background-color:transparent">:</span><span class="pln" style="margin:0px; padding:0px; border:0px; vertical-align:baseline; background-color:transparent">my_content %></span><span class="tag" style="color:#8000;margin:0px; padding:0px; border:0px; vertical-align:baseline; background-color:transparent;"></div></span></code>

content_for is how you specify which content is going to be rendered into which content area. You might have something like this:

content_for你指定的内容将被渲染到内容区域。你可能会有这样的事情：

<code style="margin:0px; padding:0px; border:0px; vertical-align:baseline; font-family:Consolas,Menlo,Monaco,'Lucida Console','Liberation Mono','DejaVu Sans Mono','Bitstream Vera Sans Mono','Courier New',monospace,serif; white-space:inherit"><span class="pun" style="margin:0px; padding:0px; border:0px; vertical-align:baseline; background-color:transparent"><%</span><span class="pln" style="margin:0px; padding:0px; border:0px; vertical-align:baseline; background-color:transparent"> content_for </span><span class="pun" style="margin:0px; padding:0px; border:0px; vertical-align:baseline; background-color:transparent">:</span><span class="pln" style="margin:0px; padding:0px; border:0px; vertical-align:baseline; background-color:transparent">my_content </span><span class="kwd" style="color:#008b;margin:0px; padding:0px; border:0px; vertical-align:baseline; background-color:transparent;">do</span><span class="pln" style="margin:0px; padding:0px; border:0px; vertical-align:baseline; background-color:transparent"> %>  This is the content.</span><span class="pun" style="margin:0px; padding:0px; border:0px; vertical-align:baseline; background-color:transparent"><%</span><span class="pln" style="margin:0px; padding:0px; border:0px; vertical-align:baseline; background-color:transparent"> </span><span class="kwd" style="color:#008b;margin:0px; padding:0px; border:0px; vertical-align:baseline; background-color:transparent;">end</span><span class="pln" style="margin:0px; padding:0px; border:0px; vertical-align:baseline; background-color:transparent"> %></span></code>

The result would be

<code style="margin:0px; padding:0px; border:0px; vertical-align:baseline; font-family:Consolas,Menlo,Monaco,'Lucida Console','Liberation Mono','DejaVu Sans Mono','Bitstream Vera Sans Mono','Courier New',monospace,serif; white-space:inherit"><span class="tag" style="color:#8000;margin:0px; padding:0px; border:0px; vertical-align:baseline; background-color:transparent;"><div></span><span class="pln" style="margin:0px; padding:0px; border:0px; vertical-align:baseline; background-color:transparent">  </span><span class="tag" style="color:#8000;margin:0px; padding:0px; border:0px; vertical-align:baseline; background-color:transparent;"><h1></span><span class="pln" style="margin:0px; padding:0px; border:0px; vertical-align:baseline; background-color:transparent"> This is the wrapper!</span><span class="tag" style="color:#8000;margin:0px; padding:0px; border:0px; vertical-align:baseline; background-color:transparent;"></h1></span><span class="pln" style="margin:0px; padding:0px; border:0px; vertical-align:baseline; background-color:transparent">  This is the content.</span><span class="tag" style="color:#8000;margin:0px; padding:0px; border:0px; vertical-align:baseline; background-color:transparent;"></div></span></code>

They are opposite ends of the rendering process, with yield specifying where content goes, and content_for specifying what the actual content is.

他们在渲染过程的两端，与yield 规定内容去哪里，和content_for指定实际的内容是什么。

Is there a generally accepted best practice?

The best practice is to use yield in your layouts, and content_for in your views. There is a special second use for content_for, where you give it no block and it returns the previously rendered content. This is primarily for use in helper methods where yield cannot work. Within your views, the best practice is to stick to yield :my_content to recall the content, and content_for :my_content do...end to render the content.

最好的方法是将yield 用在layout中，content_for 用在view中；content_for 有另外的一种用法，当不传block给它时，它将返回之前呈现的内容；这主要用在helper中，yeild不能工作；在view中，content_for 最好用于呈现内容，yield 最好用于调取内容。

转自：http://stackoverflow.com/questions/13150983/rails-what-is-the-difference-between-content-for-and-yield