[SalesForce] Which constructor will be called at the time of page load in below scenario

I have written controller like below with some overloaded constructors – 

public with sharing class TestController {
    public TestController() { }

    public TestController(ApexPages.StandardSetController controller) 
    {    
        pageInit();
    }

    public TestController(ApexPages.StandardController stdController) 
    {     
        pageInit();
    }    
}

Page code is something like this –

<apex:page standardController="Opportunity"
        recordSetVar="Opportunity" title="Select Opportunity"
        extensions="TestController" wizard="false" sidebar="false" showHeader="false"
        tabStyle="Opportunity" readOnly="false" cache="false">

</apex:page>

1) How to identify which constructor will be called at the time of page load when overloaded constructors are there?

2) In the above scenario is there any way to call default constructor at the time of page load?

Best Answer

Which constructor will be called for an extension?

The constructor for an extension used in the Apex is determined by the VisualForce page, based on the recordsetVar attribute.

If recordsetVar is defined in the apex:page element, the platform will try to inject an ApexPages.StandardSetController and will fail if there is no constructor that takes one as parameter.

If recordsetVar is not set, the platform will try to inject an ApexPages.StandardController.

Can the default constructor be called?

Yes, by defining your VF page to load the class as a controller, not an extension. If the page is defined with standardController="Opportunity" extensions="MyClass" then MyClass will be instantiated as a controller extension, with a standard controller or standard set controller injected into it, as above. If the page is defined as controller="MyClass" then MyClass will be instantiated as controller in its own right, with nothing injected, using the default constructor.

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