我是Ruby on Rails的新手，并且我正在学习使用Angular，但在我运行＆＃34; gem install rack-cors＆＃34;后，当我尝试启动rails应用程序时，我保持收到此错误：
C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/actionpack-5.1.1/lib/action_dispatch/middleware/stack.rb:35:in `build': undefined method `new' for "Rack::Cors":String (NoMethodError)
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from C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/actionpack-5.1.1/lib/action_dispatch/middleware/stack.rb:99:in `block in build'
from C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/actionpack-5.1.1/lib/action_dispatch/middleware/stack.rb:99:in `each'
from C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/actionpack-5.1.1/lib/action_dispatch/middleware/stack.rb:99:in `inject'
from C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/actionpack-5.1.1/lib/action_dispatch/middleware/stack.rb:99:in `build'
from C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/railties-5.1.1/lib/rails/engine.rb:508:in `block in app'
from C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/railties-5.1.1/lib/rails/engine.rb:504:in `synchronize'
from C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/railties-5.1.1/lib/rails/engine.rb:504:in `app'
from C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/railties-5.1.1/lib/rails/application/finisher.rb:45:in `block in <module:Finisher>'
from C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/railties-5.1.1/lib/rails/initializable.rb:30:in `instance_exec'
from C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/railties-5.1.1/lib/rails/initializable.rb:30:in `run'
from C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/railties-5.1.1/lib/rails/initializable.rb:59:in `block in run_initializers'
from C:/Ruby23-x64/lib/ruby/2.3.0/tsort.rb:228:in `block in tsort_each'
from C:/Ruby23-x64/lib/ruby/2.3.0/tsort.rb:350:in `block (2 levels) in each_strongly_connected_component'
from C:/Ruby23-x64/lib/ruby/2.3.0/tsort.rb:431:in `each_strongly_connected_component_from'
from C:/Ruby23-x64/lib/ruby/2.3.0/tsort.rb:349:in `block in each_strongly_connected_component'
from C:/Ruby23-x64/lib/ruby/2.3.0/tsort.rb:347:in `each'
from C:/Ruby23-x64/lib/ruby/2.3.0/tsort.rb:347:in `call'
from C:/Ruby23-x64/lib/ruby/2.3.0/tsort.rb:347:in `each_strongly_connected_component'
from C:/Ruby23-x64/lib/ruby/2.3.0/tsort.rb:226:in `tsort_each'
from C:/Ruby23-x64/lib/ruby/2.3.0/tsort.rb:205:in `tsort_each'
from C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/railties-5.1.1/lib/rails/initializable.rb:58:in `run_initializers'
from C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/railties-5.1.1/lib/rails/application.rb:353:in `initialize!'
from D:/TFE Unipar/Vigia Back-End/config/environment.rb:5:in `<top (required)>'
from config.ru:3:in `require_relative'
from config.ru:3:in `block in <main>'
from C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/rack-2.0.2/lib/rack/builder.rb:55:in `instance_eval'
from C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/rack-2.0.2/lib/rack/builder.rb:55:in `initialize'
from config.ru:in `new'
from config.ru:in `<main>'
from C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/rack-2.0.2/lib/rack/builder.rb:49:in `eval'
from C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/rack-2.0.2/lib/rack/builder.rb:49:in `new_from_string'
from C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/rack-2.0.2/lib/rack/builder.rb:40:in `parse_file'
from C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/rack-2.0.2/lib/rack/server.rb:319:in `build_app_and_options_from_config'
from C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/rack-2.0.2/lib/rack/server.rb:219:in `app'
from C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/railties-5.1.1/lib/rails/commands/server/server_command.rb:24:in `app'
from C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/rack-2.0.2/lib/rack/server.rb:354:in `wrapped_app'
from C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/railties-5.1.1/lib/rails/commands/server/server_command.rb:80:in `log_to_stdout'
from C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/railties-5.1.1/lib/rails/commands/server/server_command.rb:42:in `start'
from C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/railties-5.1.1/lib/rails/commands/server/server_command.rb:131:in `block in perform'
from C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/railties-5.1.1/lib/rails/commands/server/server_command.rb:126:in `tap'
from C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/railties-5.1.1/lib/rails/commands/server/server_command.rb:126:in `perform'
from C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/thor-0.19.4/lib/thor/command.rb:27:in `run'
from C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/thor-0.19.4/lib/thor/invocation.rb:126:in `invoke_command'
from C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/thor-0.19.4/lib/thor.rb:369:in `dispatch'
from C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/railties-5.1.1/lib/rails/command/base.rb:63:in `perform'
from C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/railties-5.1.1/lib/rails/command.rb:44:in `invoke'
from C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/railties-5.1.1/lib/rails/commands.rb:16:in `<top (required)>'
from bin/rails:4:in `require'
from bin/rails:4:in `<main>
这是错误中提到的文件：
require "active_support/inflector/methods"
require "active_support/dependencies"
module ActionDispatch
class MiddlewareStack
class Middleware
attr_reader :args, :block, :klass
def initialize(klass, args, block)
@klass = klass
@args = args
@block = block
end
def name; klass.name; end
def ==(middleware)
case middleware
when Middleware
klass == middleware.klass
when Class
klass == middleware
end
end
def inspect
if klass.is_a?(Class)
klass.to_s
else
klass.class.to_s
end
end
def build(app)
klass.new(app, *args, &block)
end
end
include Enumerable
attr_accessor :middlewares
def initialize(*args)
@middlewares = []
yield(self) if block_given?
end
def each
@middlewares.each { |x| yield x }
end
def size
middlewares.size
end
def last
middlewares.last
end
def [](i)
middlewares[i]
end
def unshift(klass, *args, &block)
middlewares.unshift(build_middleware(klass, args, block))
end
def initialize_copy(other)
self.middlewares = other.middlewares.dup
end
def insert(index, klass, *args, &block)
index = assert_index(index, :before)
middlewares.insert(index, build_middleware(klass, args, block))
end
alias_method :insert_before, :insert
def insert_after(index, *args, &block)
index = assert_index(index, :after)
insert(index + 1, *args, &block)
end
def swap(target, *args, &block)
index = assert_index(target, :before)
insert(index, *args, &block)
middlewares.delete_at(index + 1)
end
def delete(target)
middlewares.delete_if { |m| m.klass == target }
end
def use(klass, *args, &block)
middlewares.push(build_middleware(klass, args, block))
end
def build(app = Proc.new)
middlewares.freeze.reverse.inject(app) { |a, e| e.build(a) }
end
private
def assert_index(index, where)
i = index.is_a?(Integer) ? index : middlewares.index { |m| m.klass == index }
raise "No such middleware to insert #{where}: #{index.inspect}" unless i
i
end
def build_middleware(klass, args, block)
Middleware.new(klass, args, block)
end
end
end
我该如何解决？
答案 0 :(得分：28)
使用Rails 5时，请删除引号。
module YourApp
class Application < Rails::Application
# ...
# Rails 3/4
config.middleware.insert_before 0, "Rack::Cors" do
allow do
origins '*'
resource '*', :headers => :any, :methods => [:get, :post, :options]
end
end
# Rails 5
config.middleware.insert_before 0, Rack::Cors do
allow do
origins '*'
resource '*', :headers => :any, :methods => [:get, :post, :options]
end
end
end
end