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CHAPTER 7 IMPROVING INTERACTION WITH AJAX
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example, we used three different callback methods. The user will see the response text from the server if the call is successful, or an error message if there s a failure. You will also see the status code of the request after the call is complete, regardless of its success or failure. You can use the callback methods in the situations that best fit your application. Table 7-3 lists the callback methods that can be used in most of the Ajax helpers.
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Table 7-3. Callback Methods for Ajax Helpers Callback
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:loading :loaded :interactive :success :failure :complete
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Triggered
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When the response from the remote call is loading After the browser is finished loading the response from the remote call When the user can start to interact with the results from the remote call When the remote request is completed, and the returned code is successful When the remote request is completed, but the return code is unsuccessful When the remote request is completed, after success or failure
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Adding a Progress Indicator
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All the functions we ve looked at so far are very powerful, but they lack a basic usability component: user feedback. Users tend to get frustrated when an application takes a while to load and there is no indicator to tell them that something is happening. They may assume that the application isn t responding and click the reload button. We can use the callback methods provided by the Ajax helpers in order to show a visual progress indicator. Replace the previous example we were working on with the code in Listing 7-5. Listing 7-5. Replacing the link_to_remote Helper in app/views/ajax/index.rhtml
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<%= link_to_remote "Ajax call with indicator", :update => "date", :loading => $('indicator').show(), :complete => $('indicator').hide(), :url => { :controller => "ajax", :action => "current_date" } %> <div id="date"><p>This text will be replaced.</p></div> <%= image_tag "indicator.gif", :id => 'indicator', :style => 'display:none' %>
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CHAPTER 7 IMPROVING INTERACTION WITH AJAX
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The image_tag function will generate HTML for the indicator.gif image, which you can download from the book s sample application code repository, and will change its display property to none, making it invisible to the user when the page loads. In the :loading callback, the indicator image will be displayed. Then it will be hidden after the request is completed, by the :complete callback. Add the code shown in Listing 7-6 to the ajax controller. This is a new action called current_date, to return the server s current date and time.
Listing 7-6. Adding the current_date Action to app/controllers/ajax_controller.rb
def current_date render :text => "<p>#{Time.now}</p>" end
Now run the example again and click the link. This time, you ll see the progress indicator before the replacement text appears, as shown in Figure 7-5.
Figure 7-5. Ajax call with a progress indicator
CHAPTER 7 IMPROVING INTERACTION WITH AJAX
Note When you run this example on your local machine, the indicator image might appear and disappear
really fast, so if you re not paying attention, you might miss it. When running on a remote server, the request time won t be quite so fast, and you ll appreciate the feedback the indicator provides. If you want to simulate long-running actions in development, you can use Ruby s sleep method, which puts a process on hold for the given number of seconds. For example, adding sleep 2 to the current_date action will ensure that you get to see the progress indicator do its thing.
Posting Forms Remotely with form_remote_tag
You ve seen the power that the link_to_remote helper provides, but so far you haven t seen an example that submits data entered by the user to the controller. With the form_remote_ tag helper, you can create a regular form that sends all the parameters to the server using an XmlHttpRequest object; however, your controller will see the upcoming requests as regular POST data. On the controller side, it needs no special treatment, so you can use the params method, or any other methods, as you usually would. Let s experiment by allowing users to create a new event using an Ajax call from a form. Start by creating the template for the event form in app/views/ajax/events.rhtml, as shown in Listing 7-7.
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