Action Components in VF Page

There are following action components in VF page:

• apex:actionSupport
• apex:actionStatus
• apex:actionRegion
• apex:actionPoller
• apex:actionFunction

apex:actionSupport:

• As name itself suggested, actionSupport provide the support to action of the other component.
• Provides support for invoking controller action methods from other Visualforce components.

<apex:page >

<apex:form>

   <apex:pageBlock>

       <apex:sectionHeader title="Rerender Example"/>     

           <apex:commandButton value="Click here!">

               <apex:actionSupport event="onmouseover" rerender="time" status="refreshstatus"/>

           </apex:commandButton>

           <apex:actionStatus id="refreshstatus" startstyle="color:green;"    startText="Refreshing...."></apex:actionStatus> 

           <apex:outputpanel id="time">

               <apex:outputtext value="{!NOW()}"/>

           </apex:outputpanel> 

   </apex:pageBlock>

</apex:form> 

</apex:page>

Explanation 

<apex:actionSupport event="onmouseover" rerender="time" status="refreshstatus"/>

The event attribute determines which action should refresh the page, we have a onmouseover. That's why when you move the mouse over the command button, the time gets refreshed..

The rerender attribute determines the portion of the page to be refreshed. We have "time" which is the ID of the portion to be refreshed....

The actionstatus attribute determines the status message to be displayed when the refresh takes place. We have "refreshstatus" which is the ID of the associated "actionstatus" tag.

apex:actionStatus

• Displays the status of an AJAX update request.
• An AJAX request can either be in progress or complete.
• When some operation is happening in the back ground then it will show processing message to the user so that she/he can wait.
• Refer the above example

apex:actionRegion

• actionRegion provides an area of a Visualforce page that decides and separates which components should be processed by the force.com server when an AJAX request is generated.
• Only the components which are inside actionregion component are processed by server, so it increases visualforce page performance.
• Refer http://www.sfdcpoint.com/salesforce/actionregion-visualforce-salesforce/ blog for the more details

apex:actionPoller

• A timer that sends an AJAX update request to the server according to a time interval that you specify

<apex:page controller="exampleCon">

    <apex:form>

        <apex:outputText value="Watch this counter: {!count}" id="counter"/>

        <apex:actionPoller action="{!incrementCounter}" rerender="counter" interval="15"/>

    </apex:form>

</apex:page>

                   

Apex Code: 

          

public class exampleCon {

    Integer count = 0;

          

    public PageReference incrementCounter() {

        count++;

        return null;

    }

          

    public Integer getCount() {

        return count;

    }

}

apex:actionFunction

• Used to call the action method of the controller from the JavaScript
• An <apex:actionFunction> component must be a child of an <apex:form> component.

Note: 

Rerender is used when you want to refresh only a portion of your visualforce page when the user does some action... This would actually improve the user interface and reduce processing time