执行’rails s’时出现NameError
我为Rails开始了这个教程。 我刚刚创建了应用程序，并打算测试默认的欢迎页面，这发生了：
D:\Programming\Rails Projects\simpleCMS>rails server C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/actionview-4.2.3/lib/action_view/helpers.rb:40:in `': uninitialized constant ActionView::Helpers::ActiveModelHelper (NameError) from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/actionview-4.2.3/lib/action_view/helpers.rb:4:in `' from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/actionview-4.2.3/lib/action_view/helpers.rb:3:in `' from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/actionview-4.2.3/lib/action_view/base.rb:5:in `require' from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/actionview-4.2.3/lib/action_view/base.rb:5:in `' from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/web-console-2.2.1/lib/web_console/template.rb:7:in `' from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/web-console-2.2.1/lib/web_console/template.rb:6:in `' from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/web-console-2.2.1/lib/web_console/template.rb:1:in `' from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/web-console-2.2.1/lib/web_console.rb:12:in `require' from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/web-console-2.2.1/lib/web_console.rb:12:in `' from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/web-console-2.2.1/lib/web-console.rb:1:in `require' from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/web-console-2.2.1/lib/web-console.rb:1:in `' from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/bundler-1.10.6/lib/bundler/runtime.rb:76:in `require' from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/bundler-1.10.6/lib/bundler/runtime.rb:76:in `block (2 levels) in require' from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/bundler-1.10.6/lib/bundler/runtime.rb:72:in `each' from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/bundler-1.10.6/lib/bundler/runtime.rb:72:in `block in require' from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/bundler-1.10.6/lib/bundler/runtime.rb:61:in `each' from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/bundler-1.10.6/lib/bundler/runtime.rb:61:in `require' from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/bundler-1.10.6/lib/bundler.rb:134:in `require' from D:/Programming/Rails Projects/simpleCMS/config/application.rb:7:in `' from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/railties-4.2.3/lib/rails/commands/commands_tasks.rb:78:in `require' from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/railties-4.2.3/lib/rails/commands/commands_tasks.rb:78:in `block in server' from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/railties-4.2.3/lib/rails/commands/commands_tasks.rb:75:in `tap' from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/railties-4.2.3/lib/rails/commands/commands_tasks.rb:75:in `server' from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/railties-4.2.3/lib/rails/commands/commands_tasks.rb:39:in `run_command!' from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/railties-4.2.3/lib/rails/commands.rb:17:in `' from bin/rails:4:in `require' from bin/rails:4:in `' 我的gemfile（没有评论）：
source 'https://rubygems.org' gem 'rails', '4.2.3' gem 'mysql2' gem 'jbuilder', '~> 2.0' gem 'sdoc', '~> 0.4.0', group: :doc group :development, :test do gem 'byebug' gem 'web-console', '~> 2.0' end gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw, :jruby]
卸载railties gem，因为只卸载rails gem不起作用。 然后安装一个旧版本的rails gem（在我的情况下为4.0.0，因为那是来自tutotial的那个）。
这解决了这个问题。
你可能需要绑定一个IP地址为什么不试试这个： rails server -b localhost