ruby-on-rails – 缺少带有{：locale => [：en],：formats =&

Missing template layouts/mailer with {:locale=>[:en],:formats=>[:html],:variants=>[],:handlers=>[:raw,:erb,:html,:builder,:ruby,:coffee,:jbuilder]}. Searched in: * “/home/ubuntu/workspace/app/views”

预览帐户激活时

这是我的user_mailer.rb

class UserMailer < ApplicationMailer

  def account_activation(user)
    @user = user
    mail to: user.email,subject: "Account activation"
  end

  def password_reset
    @greeting = "Hi"

    mail to: "to@example.org"
  end
end

并且错误突出显示的行

mail to: user.email,subject: "Account activation"

我尝试在user_mailer.rb中添加layout’mailer’,但它不起作用.

编辑：
Here is the screenshot of the error

The screenshot of my folders