rails, bootstrap, media-breakpoint-only

Question

我在网上花了一天时间试图让 bootstrap 的 media-breakpoint-only 工作但没有找到明确的说明。

我有引导导航栏工作，所以我怀疑我已经正确安装了引导。

我想让以下代码工作：

h1 {
 @include media-breakpoint-only(xs) {
   color: red;
 }
 @include media-breakpoint-only(sm) {
   color: green;
 }
 @include media-breakpoint-only(md) {
   color: blue;
 }
 @include media-breakpoint-only(lg) {
   color: yellow;
 }
 @include media-breakpoint-only(xl) {
   color: orange;
 }
}

但我不知道将这段代码放在哪里，或者我需要做哪些额外的事情才能让媒体断点正常工作。

当我将上述代码放在 application.scss 的末尾时（见下文），我收到以下错误：

未定义的 mixin 'media-breakpoint-only'。

我的 Gemfile 是

source 'https://rubygems.org'
git_source(:github) { |repo| "https://github.com/#{repo}.git" }

ruby '2.5.1'

# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
gem 'rails', '~> 5.2.0'
# Use postgresql as the database for Active Record
gem 'pg', '>= 0.18', '< 2.0'
# Use Puma as the app server
gem 'puma', '~> 3.11'
# Use SCSS for stylesheets
gem 'sass-rails', '~> 5.0'
# Use Uglifier as compressor for JavaScript assets
gem 'uglifier', '>= 1.3.0'
# See https://github.com/rails/execjs#readme for more supported runtimes
# gem 'mini_racer', platforms: :ruby

# Shnelvar
gem 'jquery-rails' 

# Use CoffeeScript for .coffee assets and views
gem 'coffee-rails', '~> 4.2'
# Turbolinks makes navigating your web application faster. Read more: https://github.com/turbolinks/turbolinks
gem 'turbolinks', '~> 5'
# Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder
gem 'jbuilder', '~> 2.5'
# Use Redis adapter to run Action Cable in production
# gem 'redis', '~> 4.0'
# Use ActiveModel has_secure_password
# gem 'bcrypt', '~> 3.1.7'

# Use ActiveStorage variant
# gem 'mini_magick', '~> 4.8'

# Use Capistrano for deployment
# gem 'capistrano-rails', group: :development

# Reduces boot times through caching; required in config/boot.rb
gem 'bootsnap', '>= 1.1.0', require: false

group :development, :test do
  # Call 'byebug' anywhere in the code to stop execution and get a debugger console
  gem 'byebug', platforms: [:mri, :mingw, :x64_mingw]
end

group :development do
  # Access an interactive console on exception pages or by calling 'console' anywhere in the code.
  gem 'web-console', '>= 3.3.0'
  gem 'listen', '>= 3.0.5', '< 3.2'
  # Spring speeds up development by keeping your application running in the background. Read more: https://github.com/rails/spring
  gem 'spring'
  gem 'spring-watcher-listen', '~> 2.0.0'
end

group :test do
  # Adds support for Capybara system testing and selenium driver
  gem 'capybara', '>= 2.15', '< 4.0'
  gem 'selenium-webdriver'
  # Easy installation and use of chromedriver to run system tests with Chrome
  gem 'chromedriver-helper'
end

# Windows does not include zoneinfo files, so bundle the tzinfo-data gem
gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw, :jruby]

gem 'bootstrap-sass', '~> 3.3', '>= 3.3.7'
gem 'bootstrap', '~> 4.1.3'

应用程序.js

// This is a manifest file that'll be compiled into application.js, which will include all the files
// listed below.
//
// Any JavaScript/Coffee file within this directory, lib/assets/javascripts, or any plugin's
// vendor/assets/javascripts directory can be referenced here using a relative path.
//
// It's not advisable to add code directly here, but if you do, it'll appear at the bottom of the
// compiled file. JavaScript code in this file should be added after the last require_* statement.
//
// Read Sprockets README (https://github.com/rails/sprockets#sprockets-directives) for details
// about supported directives.
//
//= require jquery


//= require rails-ujs

// Shnelvar
// From https://github.com/rails/jquery-rails
//   If you are running Rails 5.1 and up, and if you have included //= require rails-ujs, then jquery_ujs is not needed anymore. You can just add:
// require jquery_ujs


//= require activestorage
//= require turbolinks
//= require_tree .

// Shnelvar
//   See https://github.com/twbs/bootstrap-rubygem
//= require jquery3
//= require popper
//= require bootstrap-sprockets

应用程序.scss

/*
 * This is a manifest file that'll be compiled into application.css, which will include all the files
 * listed below.
 *
 * Any CSS and SCSS file within this directory, lib/assets/stylesheets, or any plugin's
 * vendor/assets/stylesheets directory can be referenced here using a relative path.
 *
 * You're free to add application-wide styles to this file and they'll appear at the bottom of the
 * compiled file so the styles you add here take precedence over styles defined in any other CSS/SCSS
 * files in this directory. Styles in this file should be added after the last require_* statement.
 * It is generally better to create a new file per style scope.
 *
 * require_tree .
 * require_self
 */

// See 
//  https://www.youtube.com/watch?v=vcBXXOdPfgE&index=8&list=PLYM1n9xxMy4ClO2GjX73U3BLsXx9Z7wh5
$navbar-default-bg: red;

// Shnelvar
//   See https://github.com/twbs/bootstrap-sass
@import "bootstrap-sprockets";

// Custom bootstrap variables must be set or imported *before* bootstrap.
@import "bootstrap";

// Shnelvar
//   For ralph-shiny-button etc.
@import "ralph";

// Shnelvar
//   See https://stackoverflow.com/questions/33404154/bootstrap-change-the-navbar-font-size
//   See https://teamtreehouse.com/community/how-do-you-change-the-bootstrap-font-style
.nav a{
    color: white !important;
    // font-size: 3.8em !important;
    font-size: 2.8em;
    }

Answer 1

这很可能是因为您在自己的样式表之后导入了引导样式表。看，application.css 文件中的* require_tree . 表示您从app/assets/stylesheets 导入所有样式表，因此您会收到错误，因为当时引导程序的mixin 尚不可用。

例如，要修复它，我建议创建一个全局样式表文件。 app/assets/stylesheets/main.scss，您可以在其中以正确的顺序导入所有内容。

// app/assets/stylesheets/main.scss
$navbar-default-bg: red;

@import "bootstrap-sprockets"
@import "bootstrap"

@import "some-file"   // import specific file from app/assets/stylesheets/
@import "some-dir/*"  // import whole directory from app/assets/stylesheets/

// any other styles here

在application.css 中只保留：

/*
 * This is a manifest file that'll be compiled into application.css, which will include all the files
 * listed below.
 *
 * Any CSS and SCSS file within this directory, lib/assets/stylesheets, or any plugin's
 * vendor/assets/stylesheets directory can be referenced here using a relative path.
 *
 * You're free to add application-wide styles to this file and they'll appear at the bottom of the
 * compiled file so the styles you add here take precedence over styles defined in any other CSS/SCSS
 * files in this directory. Styles in this file should be added after the last require_* statement.
 * It is generally better to create a new file per style scope.
 *
 * require main
 * require_self
 */