Rails视图嵌套布局：命名yield失效但匿名yield正常

Hey there, let's fix that named yield issue you're having with nested layouts in Rails. I spot a couple of small mistakes in your setup that are causing the :main_content yield to not render anything. Let's walk through the fixes step by step.

Critical Mistake 1: Your PWA layout is misnamed as a partial #

You named it _pwa.html.erb, but Rails expects layout files in app/views/layouts/ to be full template files (no leading underscore). The underscore tells Rails it's a partial, not a proper layout, which breaks the nested layout logic. Rename it to pwa.html.erb.

Fix the nested layout structure #

Your application.html.erb is the base layout, so your pwa.html.erb needs to properly nest inside it. Here are two correct ways to write the PWA layout:

Option 1: Use content_for to pass content to the base layout #

<%# app/views/layouts/pwa.html.erb %>
<% content_for :body do %>
  <div class="container">
    <%= yield :main_content %>
  </div>
<% end %>

<%= render template: "layouts/application" %>

Option 2: Declare the parent layout directly with the layout helper #

<%# app/views/layouts/pwa.html.erb %>
<% layout 'application' do %>
  <div class="container">
    <%= yield :main_content %>
  </div>
<% end %>

Ensure content_for runs before rendering the layout #

Your view file (view.html.erb) was cut off, but the key rule is: the content_for :main_content block needs to execute before you render the PWA layout. Here are two working approaches:

Approach 1: Write content_for directly in the view #

<%# app/views/your_controller/view.html.erb %>
<% content_for :main_content do %>
  <h1>Test</h1>
<% end %>

<%= render layout: "layouts/pwa" %>

Approach 2: Use a partial for reusable content #

Keep your _partial.html.erb as is (partials do use leading underscores):

<%# app/views/your_controller/_partial.html.erb %>
<% content_for :main_content do %>
  <h1>Test</h1>
<% end %>

Then in your view file, render the partial first, then the layout:

<%# app/views/your_controller/view.html.erb %>
<%= render partial: "partial" %>
<%= render layout: "layouts/pwa" %>

Why this works #

When you run content_for :main_content, Rails stores that content in a buffer. When the layout calls yield :main_content, it pulls from that buffer. If you render the layout before running content_for, the buffer is empty—hence nothing shows up. Also, using a proper layout file (no underscore) ensures Rails treats it as a layout template, not a partial, so the nested yield logic functions correctly.

内容的提问来源于stack exchange，提问作者james