我已经为这个问题解决了1个小时，却没有弄清为什么它不起作用。

我不使用gem devise。 我有用户模型，发布模型，UsersController.rb，PostsController.rb和以下1个帮助程序

1. PostsController.rb：

class PostsController < ApplicationController
  before_action :set_post,only: [:show,:edit,:update,:destroy]

  # GET /posts
  # GET /posts.json
  def index
    @posts = Post.all
  end

  # GET /posts/1
  # GET /posts/1.json
  def show
  end

  # GET /posts/new
  def new
    @post = Post.new
  end

  # GET /posts/1/edit
  def edit
  end

  # POST /posts
  # POST /posts.json
  def create
    @post = current_user.posts.build(post_params)

    respond_to do |format|
      if @post.save
        format.html { redirect_to @post,notice: 'Post was successfully created.' }
        format.json { render :show,status: :created,location: @post }
      else
        format.html { render :new }
        format.json { render json: @post.errors,status: :unprocessable_entity }
      end
    end
  end

  # PATCH/PUT /posts/1
  # PATCH/PUT /posts/1.json
  def update
    respond_to do |format|
      if @post.update(post_params)
        format.html { redirect_to @post,notice: 'Post was successfully updated.' }
        format.json { render :show,status: :ok,location: @post }
      else
        format.html { render :edit }
        format.json { render json: @post.errors,status: :unprocessable_entity }
      end
    end
  end

  # DELETE /posts/1
  # DELETE /posts/1.json
  def destroy
    @post.destroy
    respond_to do |format|
      format.html { redirect_to posts_url,notice: 'Post was successfully destroyed.' }
      format.json { head :no_content }
    end
  end

  private
    # Use callbacks to share common setup or constraints between actions.
    def set_post
      @post = Post.find(params[:id])
    end

    # Never trust parameters from the scary internet,only allow the white list through.
    def post_params
      params.require(:post).permit(:caption,:user_id)
    end
end

1. ApplicationHelper.rb

module ApplicationHelper
    def current_user
        session[:user_id] && User.find(session[:user_id])
    end
end

current_user帮助器方法对所有视图都适用。

据我了解，PostsController继承自ApplicationController，因此它从ApplicationHelper获取所有帮助程序。我仍然不知道为什么这行不通。

感谢您的帮助。