Notifying the containing page controller_Visualforce Development Cookbook-QQ阅读中文玄幻网

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Notifying the containing page controller

In the earlier recipes, we have seen how components can accept an attribute that is a property from the containing page controller and update the value of the property in response to a user action. If the containing page controller needs to determine if the property has changed, it must capture the previous value of the property and compare that with the current value. The same applies if the attribute passed to the component is a field from an sObject managed by the parent page controller.

In this recipe we will create a custom component that can notify its containing page controller when an attribute value is changed. In order to avoid tying the component to a particular page controller class, we will create an interface that defines the method to be used to notify the page controller. This will allow the component controller to notify any page controller that implements the interface.

Note

Interfaces define a "contract" between the calling code and the implementing code. The calling code is able to rely on the method(s) defined in the interface being available without having to know the details of the underlying code that is implementing the interface. This allows the implementing code to be swapped in and out without affecting the calling code.

Getting ready

This recipe requires that you have already completed the Multiselecting related objects recipe, as it relies on the custom sObjects created in that recipe.

How to do it…

First, create the interface by navigating to the Apex Classes setup page by clicking on Your Name | Setup | Develop | Apex Classes.
Click on the New button.
Paste the contents of the Notifiable.cls Apex class from the code download into the Apex Class area.
Click on the Save button.
Next, create the component controller by navigating to the Apex Classes setup page by clicking on Your Name | Setup | Develop | Apex Classes.
Click on the New button.
Paste the contents of the NotifyingMultiSelectRelatedController.cls Apex class from the code download into the Apex Class area.
Click on the Save button.
Next, create the custom component by navigating to the Visualforce Components setup page by clicking on Your Name | Setup | Develop | Components.
Click on the New button.
Enter NotifyingMultiSelectRelated in the Label field.
Accept the default NotifyingMultiSelectRelated that is automatically generated for the Name field.
Paste the contents of the NotifyingMultiSelectRelated.component file from the code download into the Visualforce Markup area and click on the Save button.
Next, create the custom controller for the Visualforce page by navigating to the Apex Classes setup page by clicking on Your Name | Setup | Develop | Apex Classes.
Click on the New button.
Paste the contents of the NotifiableAccountGroupController.cls Apex class from the code download into the Apex Class area.
Click on the Save button.
Next, create the Visualforce page by navigating to the Visualforce setup page by clicking on Your Name | Setup | Develop | Pages.
Click on the New button.
Enter NotifiableAccountGroup in the Label field.
Accept the default NotifiableAccountGroup that is automatically generated for the Name field.
Paste the contents of the NotifiableAccountGroup.page file from the code download into the Visualforce Markup area and click on the Save button.
Navigate to the Visualforce setup page by clicking on Your Name | Setup | Develop | Pages.
Locate the entry for the NotifiableAccountGroup page and click on the Security link.
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 NotifiableAccountGroup page: https://<instance>/apex/NotifiableAccountGroup.

Here, <instance> is the Salesforce instance specific to your organization, for example, na6.salesforce.com, and <account_id> is the ID of an account from your Salesforce instance.

When accounts are moved between the Available and Selected lists, the component controller notifies the parent page controller, which writes a message into the page with the notification details.

The parent page controller, NotifiableAccountGroupController, implements the Notifiable interface.

public with sharing class NotifiableAccountGroupController
          implements Notifiable

The implementation of the notify method wraps the notification text in an ApexPages.Message class and adds this to the messages for the page.

public void notify(String detail)
{
  ApexPages.addMessage(new ApexPages.Message(
    ApexPages.Severity.INFO, 'Notified - ' + detail));
}

The custom component takes a parameter of type Notifiable, which is assigned to a property in its controller.

<apex:attribute name="notify" 
   description="The entity to notify when the selection changes" 
   type="Notifiable" assignTo="{!notifiable}" />

The custom component also takes a rerender parameter, which is used to update part of the containing page when the selection changes.

<apex:attribute name="rerender" 
description="The component to rerender when the selection changes" 
   type="String" />

In this case, the page passes through the ID of its <apex:pageMessages /> component to display the message added in the page controller's notify method as described earlier.

When the action methods to move accounts between the Available and Selected lists are executed, these invoke the notify method with details of the change.

if (null!=notifiable)
{
  notifiable.notify('Values deleted - now ' + selected.value);
}