Why flash message won't disappear?

ruby-on-rails

I am doing some exception handling in my controller, when there is an exception thrown in :create action, I will render to the :new action and show a flash message.

Everything works fine, I can see the flash message when exception caught, but when I redirect to(handly click) other page, the flash message still here. Then I redirect to another page(the second handly click), the message could disappear.

Anyone who knows what is the reason?

My controller code:

class MessagesController < ApplicationController
  rescue_from Exception, :with => :render_new

  def new
  end

  def create
  end

private
  def render_new
    flash[:alert] = t("uploading_error")
    render :action => :new
  end
end

My layout code (Haml):

%body
  #content
    - unless flash[:alert].blank?
      #alert= flash[:alert]

Replace

flash[:alert] = t("uploading_error")

with

flash.now.alert = t("uploading_error")

and see if that is the result you expect?

flash[:alert] will stay around for the next page (hence it only disappears at the second redirect); but flash.now.alert will only display for the current page.

Deciding between flash.now and regular flash is a pain in the ass and quite fragile in my experience. I use regular flash and then modify my partial which displays the flashes to delete the contents of each flash after the user has seen it. I think this is better because

a) you don't have to think about it

b) "has the user seen it?" (ie "has the flashes partial been rendered out?") is the best criterion for deciding whether or not to clear the flash, rather than any logic in your app.

My flash partial looks like this - i also use a bit of jquery just to highlight the flashes (ie make them flash yellow for a second):

<div id="flashes">

  <% if flash[:notice] %>
    <p id="flash_notice" class="messages notice"><%= flash[:notice] %></p>
    <%= javascript_tag "$('#flash_notice').effect('highlight',{},1000);" %>
  <% end %>

  <% if flash[:error] || flash[:errors] %>
    <p id="flash_errors" class="messages errors"><%= flash[:error] || flash[:errors] %></p>
    <%= javascript_tag "$('#flash_errors').effect('highlight',{},1000);" %>
  <% end %>

  <% flash[:error] = flash[:errors] = flash[:notice] = nil %>
</div>

An alternative is to use flash.clear at the end of the partial like so:

<% if !flash.empty? %>
  <div class="flash-messages-container">
    <% flash.each do |name, msg| %>
      <% if msg.is_a?(String) && [:success, :info, :error, :warning].include?(name) %>
        <div class="flash-message" data-type="<%= name %>" >
          <%= msg %>
        </div>
      <% end %>
    <% end %>
  </div>
  <% flash.clear %>
<% end %>

I also suggest to clear the flash inner hashes upon displaying. flash.clear will do the trick in a clean way :

      <% flash.each do |key, value| %>
       <div class="alert alert-<%= key %>">
        <%= value %>
       </div>
      <% end %>
      <% flash.clear %> #this line clears the object

http://api.rubyonrails.org/classes/ActionDispatch/Flash/FlashHash.html#method-i-clear

Even this does not work......certain types of exceptions like syntax errors...will prevent any type of cookie, flash or parameters from being transferred from controller to view. Your only option is to use a session key and then clear it after showing the error.

Try your solution with a syntax error...you should see that your message won't appear in the redirected page with anything else except with a session key.....

Why flash message won't disappear?

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