View state and transient

Question

This is for academic purposes

I am trying to run some code from visualforce in practise and came across this sample page and related controller

page is

<apex:page controller=”myController” >
<apex:form >
<apex:pageBlock title=”My Content” mode=”edit”>
<apex:pageBlockButtons >
<apex:commandButton action=”{!save}” value=”Save”/>
</apex:pageBlockButtons>
<apex:pageBlockSection title=”My Content Section”
columns=”2”>
<apex:outputLabel for=”aName”>Account Name:</
apex:outputLabel>
<apex:inputText value=”{!accountName}”/>
</apex:pageBlockSection>
</apex:pageBlock>
</apex:form>
</apex:page>

controller code is

public with sharing class myController {
private final Id accountId ;
transient public final String accountName {get; set; }
public myController() {
Account account = [select Id, Name from Account where id
=:ApexPages.currentPage().getParameters().get(‘id’)];
accountId = account.Id ;
accountName = account.Name ;
}
public PageReference save() {
Account myAccount = [select name from Account where id
=:accountId];
myAccount.name = accountName;
update myAccount;
return null;
}
}

where i am confused is,

myAccount.name = accountName;

This code works like this:

Page gets pre populated with account name on load.User enters edits account name.Clicks Save.It gets saved to DB.

Now this is where i am confused:

We marked 'account name' variable as transient in controller.So how come value entered by user still persist in 'accountname' variable. When user clicks save,save method is executed during the post back request.since accountname is not view state i thought variable will not have the value entered by user

Maybe i don't understand view state properly. Can somebody clarify this please?

Answer 1

Transient variables are not stored in the view state, but can be regenerated by the post back if bound to an input element. In general, you only need to use the view state for elements not bound to an input element and need to maintain state between post backs. The standard controller for a page, for example, should not be transient, because it won't stick. However, any element bound by input elements don't need to be saved in the view state if they are rendered.

In other words, the view state is first restored into memory (deserialized), and since accountName wasn't stored in the view state (it is transient), the initial value is null. Then, Visualforce calls set(accountName, value), because it's bound to a rendered input element, which effectively restores its state. Finally, save() is called and the value is correctly populated.