apex: composition Component in Visualforce Page

 The <apex: composition> is another important component used to define an area of the page that includes content from a second template page. The template page includes one or more <apex: insert> components. The <apex: composition> component names the associated template and provides a body for the template's <apex: insert> components with matching <apex: define> components. Any content outside of an <apex: composition> component is not rendered.

We use this component to get user input from the controller method that doesn't correspond to a field on a sObject field.

The <apex: composition> component has the following attributes:

1. rendered

The rendered is a string-type attribute used for rendering the component. However, the rendered attribute does not affect the display of this component.

Syntax:

<apex: composition rendered="condition"></apex: composition>  

2. template

The template is an "ApexPages.PageReference" type used for specifying the template page used for this component. The name of the apex page or PageReference is used as a value for this attribute.

Syntax:

<apex: composition template="pageName"></apex: composition>  

Let's take an example to understand how we can use this component on the Visualforce page:

ApexCompositionExample.vfp

<!-- create apex page to understand the <apex: composition> component -->  

<apex: page >  

    <!-- use <apex: composition> for specifying the template-->  

    <apex:composition template="ApexInsertExample">  

        <!-- use <apex: define> for adding header and body-->  

        <apex:define name="header">(page)Header of ApexCompositionExample Start.</apex:define>  

        <apex:define name="body">(page)Body of ApexCompositionExample Start.</apex:define>  

    </apex: composition>  

</apex: page>  

ApexInsertExample.vfp

<!-- create an apex page that acts as the template-->  

<apex: page >  

    <!-- use outputText and insert component -->  

    <apex:outputText value="(template) This is before the header"/><br/>  

    <apex:insert name="header"/><br/>  

    <apex:outputText value="(template) This is between the header and body"/><br/>  

    <apex:insert name="body"/>  

</apex: page>