Action Components

Action components allow the page to invoke a method on the controller. The controller method typically performs some operation on the contents of the page, such as updating the database, and then either refreshes the page or navigates to a new page.

Before any refreshing or navigation takes place, the state of the user interface input elements on the page is injected into the variables of the controller using setters. This way, they are accessible from within your action code.

The two basic action components are commandButton and commandLink. The commandButton is rendered as an HTML button, whereas the commandLink is rendered as an anchor. Both are valid only inside a form component. They are typically used with an action attribute that specifies the name of the controller method to invoke or the URL of a new page to navigate to and a value attribute that displays a label to the user. Listing 6.14 is an example of using the commandButton, which invokes the doSomething method of the controller when clicked.

Listing 6.14 Sample Usage of commandButton Component

Click here to view code image

<apex:form>
  <apex:commandButton action="{!doSomething}"
    value="Do Something" />
</apex:form>

The page component also has an action, specified in the init attribute. This action is called automatically upon page load but should not be used for initialization code. Its purpose is to immediately redirect the user to a new page.

Before invoking a controller method, all action components perform validation on data components, accepting user input that is contained within their parent form. For example, if an input component is required but no value is provided, an error results. Errors can be displayed using the pageMessages or messages component (described in the “Error Handling” subsection of this chapter) and beside any inputField components if their database field is defined to do so. You can disable this validation behavior by setting the action component’s immediate attribute to true.