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R@jeshR@jesh 

Difference between rendered, renderAs and reRerender in Visualforce

NehalNehal (Salesforce Developers) 
Hi,

Please refer below links that will explain you on this:
1.http://www.infallibletechie.com/2012/10/difference-between-rendered-renderas.html
2.http://www.cloudforce4u.com/2013/07/render-and-rerender-in-salesforce.html
3.http://sfdc2u.blogspot.co.uk/2013/05/difference-between-rendered-renderas.html
4.http://www.salesforce.com/us/developer/docs/pages/Content/pages_compref_actionRegion.htm
5.http://learn4sfdc.blogspot.co.uk/2014/01/what-is-difference-in-render-rerender.html
6.http://www.codetalks.in/2013/08/salesforce-visualforce-rendered.html
7.http://nirmalchristopher.blogspot.co.uk/2014/02/renderedrender-as-re-render-example-in.html

I hope this helps.

Please mark this as a "Best Answer" if this has resolved your issue.
praveen murugesanpraveen murugesan
Hi Rajesh,

Rendered:

This to rendered(ie., display) particular filed or section based on boolean value.  In the controller you need to have get method to assign the value for this variable.

Eg:

<apex:inputField value="{obj.Filed_C}"  Rendered="{!val == true}"/>

controller:

public boolean val{get;set;}

method(){
val = true;
}


RederAs:

It is render a VF page as PDF or some other

Eg:

<apex:page controller="mmm" rederAs="pdf">

ReRender:

This is to ReReder(ie.,Reload) some fields, or sections  after some operation/change. For this you need to assign id to field, sections. 

Eg:

<apex:actionRegion >
     <apex:inputField value="{!xxxx}"  >   
                        <apex:actionSupport event="onchange" rerender="yrs,yrss,yrsss,nodays,nohours,nominutes" action="{!xxx}" >
                            <apex:param name="Para" value="{!rowNum}" assignTo="{!IndexValue}" />                            
                        </apex:actionSupport>
                    </apex:inputField>   
                </apex:actionRegion>
</apex:inputFiel>

yrs,yrss,yrsss,nodays,nohours,nominutes  are the id's of field and sections

I hope now you have basic idea of this.

Thanks

Praveen Murugesan.
Tejpal KumawatTejpal Kumawat
Hello Rajesh,

1. Rendered : It use to place condition for a component(Field, outptpanel, section etc), that will show or not on page.
2. ReRender : It is use after a ajax call, Is comonent will again check condition for that component.
3. RederAs : It is use for  Visualforce page show  as PDF file or other

Thanks
Arun WebmindArun Webmind
nice answer Tejpal kumawat
Gomathi SGomathi S
Rendered it is used to show and hide elements works like css in general we can say display properties
<apex:pageBlock rendered=”{!ShowpageBlock}”>
Account Name  :<apex:outputField value=”{!Account.Name}”/>
Account Number :<apex:outputField value=”{!Account.AccountNumber}”/>
</apex:pageBlock>

Rerender is used when you want to refresh only a portion
reRender= “pgblck1, pgbcl2”

RenderAs providing extension of page to create output like pdf, doc, excel
<apex:page standardController=”Account” renderAs=”pdf”>
<apex:pageBlock >
<apex:outputField value=”{!Account.name}”/>
<apex:outputField value=”{!Account.AccountNumber}”/>
</apex:pageBlock>
</apex:page>

For More Details: http://theblogreaders.com/what-is-the-difference-between-rendered-rerender-renderas-in-visualforce-page/

Salesforce Interview Questions and Answer (http://theblogreaders.com/salesforce-interview-questions-and-answer/)
venkata kalyani konakallavenkata kalyani konakalla
Rendered - it returns Boolean value (if it is true, it displays the block else it will be hidden)
reRender - ID. The particular block will be refreshed
renderAs - Display the page as pdf, excel, etc..