Casting Trigger.New to List<Case> in Trigger Framwork

Question

We are using a trigger framework by Kevin O'Hara and I have a basic question about it. Why when I use Trigger.New inside one of the methods I have to cast it to a List of cases in order to use it?

public class CaseTriggerHandler extends TriggerHandler {

    public CaseTriggerHandler() {
        this.setMaxLoopCount(35);
    }

    private static Boolean isMethod1 = false;

    protected override void beforeInsert(){
        if (!isMethod1) { 
            method1(Trigger.new); 
            isMethod1 = true;
        } 
    }

    private void method1() {

        for(Case c: (List<Case>)Trigger.New) {}      //<------------------

    }
}

If I write for(Case c: Trigger.New) then I get this error:

Operation: Compiling: C:\Users\Dante\proj\src\classes\CaseTriggerHandler.cls Timestamp: Sun, 27 Aug 2017 18:29:00 Result: [OPERATION FAILED]: classes/CaseTriggerHandler.cls: Invalid loop variable type expected SObject was Case (Line: 1324, Column: 9)

Can someone explain?

Answer 1

This is not related to the framework you are using. It is standard compiler error. Below is the list of scenarios and explanations.

Scenario 1: Trigger.New in Trigger, which works well as it is implicitly type casted to specific object, here is Case

Result: it works wells and complies

Trigger simpleTrigger on Case (after insert) {
    //works well
    for (Case a : Trigger.new) {
        // Iterate over each Case
    }
}

Scenario 2: In the Trigger handler class and in a specific method, we are receiving specific list List<Case> as an argument, and trying to loop through the specific object.

Result: it works wells and complies

public class CaseTriggerHandler
{   
    public void onAfterInsert(List<Case> oldList, List<Case> newList)
    {
        //this works fine
        for(Case a:newList)
        {

        }
    }   
}

Scenario 3: In a method, directly accessing Trigger.new which actually returns list of SObject. So, following code will works well.

Result: it works wells and complies

public class CaseTriggerHandler
{
    public void onAfterInsert()
    {
        //works well
        for(SObject a:Trigger.new)
        {
            if(a instanceOf Case)
            {
                Case caseObj = (Case) a;
            }
        }
    }
}

Scenario 4: Type casting Trigger.new to list of Case

Result: it works wells and complies

public class CaseTriggerHandler
{
    public void onAfterInsert()
    {
        //works well
        for(Case a: (List<Case>)Trigger.new)
        {

        }
    }
}

Scenario 5: Directly accessing Trigger.new without type casting to specific object.

Result: Compile Error: Invalid loop variable type expected SObject was Case

public class CaseTriggerHandler
{
    public void onAfterInsert()
    {
        //will not compile
        for(Case a: Trigger.new)
        {

        }
    }
}