rails 中提示错误的方法

　　　　我目前只学会了两种最简单的。

　　　　1.flash.

　　　　The flash provides a way to pass temporary objects between actions. Anything you place in the flash will be exposed to the very next action and then cleared out. This is a great way of doing notices and alerts, such as a create action that sets flash[:notice] = "Post successfully created" before redirecting to a display action that can then expose the flash to its template. Actually, that exposure is automatically done.

　　　　这段话是讲flash可以将临时信息保存一段时间，在不同的动作之间传递，可以用来提示信息。

class PostsController < ActionController::Base
  def create
    # save post
    flash[:notice] = "Post successfully created"
    redirect_to @post
  end

  def show
    # doesn't need to assign the flash notice to the template, that's done automatically
  end
end

show.html.erb
  <% if flash[:notice] %>
    <div class="notice"><%= flash[:notice] %></div>
  <% end %>

　　　　这是API中的实例，很简单，不赘述了。

　　　　2.直接用javascript中的alert，说来惭愧。