用戶中的參數錯誤＃pagename - 表單中的第一個參數不能包含零或爲空

Question

我在我的用戶文件夾（mypage.html.erb）下創建了一個新頁面，因爲其上的內容需要用戶數據。我創建一個表單/下拉菜單，以及用於在把下面的代碼在某種原因，我拋出這個錯誤：

undefined local variable or method `user' for #<#<Class:0x000000021aee18>:0x007fc52025c8e8> 

<%= form_for(@user) do |f| %>` `<%= user.firstname %>` `<%= user.lastname %>` 

我不知道爲什麼，因爲我知道@user定義。我創建了多個表單並在其他自定義頁面上拉取了其他用戶數據。

見代碼：

mypage.html.erb

<div id="widepage"> 
    <div class="blue-text-header">Title</div> 
    <div class="grey-text-subheader">Subtitle</div> 
    <div class="infoheaders">Information</div> 

    <%= form_for @user do |f| %> 
    <%= f.collection_select :questions, User::QUESTIONS, :to_s, :to_s, 
     :include_blank => true 
    %> 
    <%= f.submit "Create" %> 
    <% end %> 
</div> 

<div class="fullcard"> 
    <div class="name"> 
    <%= user.firstname %> <%= user.lastname %> 
    </div> 
</div> 

user.rb

class User < ActiveRecord::Base 
    def self.search(search) 
    where("firstname LIKE ? OR lastname LIKE ?", "%#{search}%", "%#{search}%") 
    end 

    QUESTIONS = ['hot', 'medium', 'cold'] 

    has_secure_password 

    validates_length_of :password, :in => 6..20, :on => :create 
    validates :password_confirmation, presence: true, if: -> { new_record? || changes["password"] } 

    has_attached_file :avatar, 
    :path => ":rails_root/public/system/:attachment/:id/:basename_:style.:extension", 
    :url => "/system/:attachment/:id/:basename_:style.:extension", 
    :styles => { 
     :thumb => ['150x150#', :jpg, :quality => 100], 
     :preview => ['175x175#', :jpg, :quality => 70], 
     :large => ['600>',  :jpg, :quality => 70], 
     :retina => ['1200>',  :jpg, :quality => 30] 
    }, 
    :convert_options => { 
     :thumb => '-set colorspace sRGB -strip', 
     :preview => '-set colorspace sRGB -strip', 
     :large => '-set colorspace sRGB -strip', 
     :retina => '-set colorspace sRGB -strip -sharpen 0x0.5' 
    } 

    validates_attachment :avatar, 
    :presence => true, 
    :size => { :in => 0..10.megabytes }, 
    :content_type => { :content_type => /^image\/(jpeg|png|gif|tiff)$/ } 
end 

users_controller.rb

class UsersController < ApplicationController 
    def create 
    @user = User.new(user_params) 
    if @user.save 
     flash[:success] = "You signed up successfully" 
     flash[:color] = "valid" 
     redirect_to @user 
    else 
     flash[:notice] = "Form is invalid" 
     flash[:color] = "invalid" 
     render "new" 
    end 
    end 

    def mypage 
    @user = User.new 
    end 

    def index 
    @user = User.all 
    if params[:search] 
     @user = User.search(params[:search]).order("created_at DESC") 
    else 
     @user = User.all.order('created_at DESC') 
    end 
    end 

    def show 
    @user = User.find(params[:id]) 
    end 

    def edit 
    @user = User.find(params[:id]) 
    end 

    def update 
    @user = User.find(params[:id]) 
    if @user.update_attributes(user_params) 
     redirect_to @user 
    else 
     render 'edit' 
    end 
    end 

    private 
    def user_params 
    params.require(:user).permit(:firstname, :lastname, :email, :aptno, :streetaddress, :city, :country, :stateprov, :poszip, :receive_newsletters, :terms_accepted, :password, :password_confirmation, :avatar, :bio) 
    end 

    # def user_params 
    # params.require(:user).permit(:name, :description, :avatar) 
    # end 

    def new 
    end 
end 

Answer 1

@user是一個實例變量（的ivar）。而user沒有@符號是一個局部變量。

當學習Rails時，Rails會將控制器中定義的任何實例變量傳輸到view_context，這可能會讓人感到困惑。這view_context是一個對象，其中rails填充所有實例變量和輔助方法。視圖中的view_context爲self。

所以，當你這樣做：

def mypage 
    @user = User.new 
end 

Rails會提供實例VAR @user到您的視圖。

<%= form_for(@user) do |f| %> 
    <%# ... %> 
    <%= @user.firstname %><%= @user.lastname %> 
<% end %> 

另一個很酷的技巧，如果你正在創建一個表單或部分，你不知道（伊娃），你可以使用名爲是對錶單生成器實例中使用.object：

<%= form_for(@user) do |f| %> 
    <%# ... %> 
    <%= f.object.firstname %><%= f.object.lastname %> 
<% end %> 

Answer 2

確保並初始化變量@user在你的動作和控制器

@user = User.new(params) 

Answer 3

如果我的頁面動作是在用戶控制器，首先初始化用戶對象。

def mypage 
 
    @user = User.new() 
 
end

你應該將其發送到表單之前初始化對象。

@user = User.new() 

Answer 4

在控制器

def mypage 
    @user = User.new 
end 

Answer 5

添加這種方法應該是<%= @user.firstname %> <%= @user.lastname %>