css - Rails - 当 URL 中存在参数时显示/隐藏 CSS 类

Question

在我看来，我有一个表单，我只想在其参数出现在 URL 中时显示输入:

= form_tag search_path, :method => :get do
  = select_tag 'search[type]', options_for_select([['Publishers', 'publishers'], ['Editions', 'editions'], ['Contributors', 'contributors']], selected = (params[:search][:type] rescue nil)), prompt: "Search type", :required => "true"

  = select_tag 'search[filter]', options_for_select([['Filter by', 'filter_by'], ['All', 'all']], selected = (params[:search][:filter] rescue nil)), prompt: "Select filter", :required => "true"

  - invisible = params[:search][:value].present? ? '' : 'invisible'
  = text_field_tag 'search[value]', (params[:id] || params[:search][:value] rescue nil), :required => "true", :class =>  "#{invisible}", :placeholder => "Type search"

我的想法是控制它显示一个名为“invisible”的 CSS 类，带有 display: none;，如上。但是，当我渲染 View 时，它会在我声明“不可见”的行中返回此 Rails 错误:

undefined method `[]' for nil:NilClass

怎么了？

Answer 1

这是因为当表单正在加载时，params[:search] 为 nil，而您正试图对其调用 [:filter]，因此未定义方法 [] 为 nil。

有多种解决方案，有些不错，有些不太好，选择你最喜欢的:

invisible = params[:search].try(:[], :value) ? '' : 'invisible'
invisible = params[:search] && params[:search][:value] ? '' : 'invisible'
invisible = (params[:search] || {})[:value] ? '' : 'inivisble'
invisible = (params[:search][:value] rescue nil) ? '' : 'invisible'