Ruby on rails 未定义的方法“[]'；for nil:application helper中方法的NilClass

我有一个叫做crumps的方法，意思是未定义的方法。我正在从sinatra应用程序导入代码，并尝试使其与rails应用程序一起工作

以下是方法：

def crumbs
primary, secondary = current_link
return {
    primary:   { icon: menu[primary.to_sym][:primary][:icon], label: menu[primary.to_sym][:primary][:label]},
    secondary: {
        icon:  menu[primary.to_sym][:items][secondary.to_sym][:icon],
        label: menu[primary.to_sym][:items][secondary.to_sym][:label]
    }
}
end

以下是该方法中包含的其他方法：

 def menu
  return {
    dashboard: {
        primary: { link: "dashboard", icon: "icon-dashboard", label: "Dashboard" },
        items: {
            dashboard: { icon: "icon-dashboard", label: "Dashboard" }
        }
    },
    ui_lab: {
        primary: { link: "buttons", icon: "icon-beaker", label: "UI Lab" },
        items: {
            buttons: { icon: "icon-hand-up",       label: "Buttons" },
            general: { icon: "icon-beaker",        label: "General elements" },
            icons:   { icon: "icon-info-sign",     label: "Icons"},
            grid:    { icon: "icon-th-large",      label: "Grid"},
            tables:  { icon: "icon-table",         label: "Tables"},
            widgets: { icon: "icon-plus-sign-alt", label: "Widgets"},
        }
    },
    forms: {
        primary: { link: "forms", icon: "icon-edit", label: "Forms" },
        items: {
            forms: { icon: "icon-edit", label: "Form Elements" }
        }
    },
    charts: {
        primary: { link: "charts", icon: "icon-bar-chart", label: "Charts"},
        items: {
            charts: { icon: "icon-bar-chart", label: "Charts"}
        }
    },
    other: {
        primary: { link: "wizard", icon: "icon-link", label: "Others"},
        items: {
            wizard: { icon: "icon-magic", label: "Wizard" },
            login: { icon: "icon-user", label: "Login Page" },
            sign_up: { icon: "icon-user", label: "Sign Up Page" },
            full_calendar: { icon: "icon-calendar", label: "Full Calendar" },
            error404: { icon: "icon-ban-circle", label: "Error 404 page" },
        }
    }
}
end

除了这个：

def current_link
root_path = "/"
current_route = request.url.split("/") # pages/dashboard/stats.html -> ['dashboard', 'stats.html']
return current_route.compact.first, current_route.compact.split(".").first
end

在视图中，这就是所谓的：

      <i class="<%= crumbs[:secondary][:icon] %>"></i>
        <%= crumbs[:secondary][:label] %>

---

有什么想法吗？

只需定义nil缺少的方法：

def nil.[] x
  puts "You hit the jackpot!!! You win #{x}!!!"
  # Or come up with the behavior according to your own needs.
end

撇开玩笑不谈，你的问题没有提供足够的信息来确定你真正的问题。您的一个或多个哈希似乎不包含搜索的键，然后您尝试向它发送

#[]

方法。尝试

Object#尝试
ActiveSupport
中的
方法，或编写：

def crumbs
  primary, secondary = current_link
  return {
    primary: { icon: ( menu[primary.to_sym][:primary][:icon] rescue nil ),
               label: ( menu[primary.to_sym][:primary][:label]} rescue nil ),
    secondary:
      { icon: ( menu[primary.to_sym][:items][secondary.to_sym][:icon] rescue nil ),
        label: ( menu[primary.to_sym][:items][secondary.to_sym][:label] rescue nil )
      }
    }
end

只需为nil定义缺少的方法：

def nil.[] x
  puts "You hit the jackpot!!! You win #{x}!!!"
  # Or come up with the behavior according to your own needs.
end

撇开玩笑不谈，你的问题没有提供足够的信息来确定你真正的问题。您的一个或多个哈希似乎不包含搜索的键，然后您尝试向它发送
#[]
方法。尝试
Object#尝试
ActiveSupport
中的
方法，或编写：

def crumbs
  primary, secondary = current_link
  return {
    primary: { icon: ( menu[primary.to_sym][:primary][:icon] rescue nil ),
               label: ( menu[primary.to_sym][:primary][:label]} rescue nil ),
    secondary:
      { icon: ( menu[primary.to_sym][:items][secondary.to_sym][:icon] rescue nil ),
        label: ( menu[primary.to_sym][:items][secondary.to_sym][:label] rescue nil )
      }
    }
end

查找这些内容的一种方法是将
[]
调用替换为对
：fetch
的调用。当它爆炸时，它将返回一个
KeyError
来告诉您丢失了哪把钥匙：

> mystery = { a: 1, b: 2, c: 3 }
=> {:a=>1, :b=>2, :c=>3}

> mystery[:d][:q]
NoMethodError: undefined method `[]' for nil:NilClass

> mystery.fetch(:d).fetch(:q)
KeyError: key not found: :d

查找这些内容的一种方法是将
[]
调用替换为对
：fetch
的调用。当它被炸开时，它将返回一个
KeyError
告诉您缺少哪个键：

> mystery = { a: 1, b: 2, c: 3 }
=> {:a=>1, :b=>2, :c=>3}

> mystery[:d][:q]
NoMethodError: undefined method `[]' for nil:NilClass

> mystery.fetch(:d).fetch(:q)
KeyError: key not found: :d

在返回nil-menu[primary.to_sym]#=>nil[]的链上使用[:symbol]，在返回nil-menu[primary.to_sym]#=>nil[]的链上使用[:symbol]