Turning off an action poller

The standard Visualforce <apex:actionPoller/> component sends AJAX requests to the server based on the specified time interval. An example use case is a countdown timer that sends the user to another page when the timer expires. But what if the action poller should stop when a condition in the controller becomes true, for example, when a batch apex job completes or an update is received from a third-party system?

In this recipe, we will simulate the progression of a payment through a number of states. An action poller will be used to retrieve the latest state from the server and display it to the user. Once the payment reaches the state Complete, the action poller will be disabled.

Getting ready

This recipe makes use of a custom controller, so this will need to be created before the Visualforce page.

How to do it…

1. Navigate to the Apex Classes setup page by clicking on Your Name | Setup | Develop | Apex Classes.

2. Click on the New button.

3. Paste the contents of the PollerController.cls Apex class from the code download into the Apex Class area.

   Tip

   Note that there is nowhere to specify a name for the class when creating through the setup pages; the class name is derived from the Apex code.

4. Click on the Save button.

5. Next, create the Visualforce page by navigating to the Visualforce setup page by clicking on Your Name | Setup | Develop | Pages.

6. Click on the New button.

7. Enter ActionPoller in the Label field.

8. Accept the default ActionPoller that is automatically generated for the Name field.

9. Paste the contents of the ActionPoller.page file from the code download into the Visualforce Markup area.

10. Click on the Save button to save the page.

11. Navigate to the Visualforce setup page by clicking on Your Name | Setup | Develop | Pages.

12. Locate the entry for the ActionPoller page and click on the Security link.

13. On the resulting page, select which profiles should have access and click on the Save button.

How it works…

Opening the following URL in your browser displays the ActionPoller page: https://<instance>/apex/ActionPoller.

Here, <instance> is the Salesforce instance specific to your organization, for example, na6.salesforce.com.

The page polls the server for the current state, displaying the message Polling … when the action poller executes as shown in the following screenshot:

Once the current state reaches Complete, the action poller terminates.

The key to this recipe is the enabled attribute on the actionPoller component.

<apex:actionPoller action="{!movePayment}" 
     rerender="payment" interval="5" status="status" 
     enabled="{!paymentState!='Complete'}"/>

Tip

Downloading the example code

You can download the example code files for all Packt books you have purchased from your account at http://www.packtpub.com. If you purchased this book elsewhere, you can visit http://www.packtpub.com/support and register to have the files e-mailed directly to you.

This merge field references the paymentState property from the custom controller, which is evaluated each time the action poller executes until it becomes false. At this time the action poller is permanently disabled.

The Polling … message is generated by the actionStatus component associated with the action poller. This component has a startText attribute but not a stopText attribute, which means that the text will only be displayed while the AJAX request is in progress.

<apex:actionStatus startText="Polling ..." id="status"/>

See also

• The Using action functions recipe in Chapter 7, JavaScript shows how to execute a controller.