[SalesForce] APEX: Use a dynamic string to create an instance of a class

I have an abstract class called Process that I extend to create a list of processes (List<Process>); each in relation to an object. For now everything works as expected but I'm really hoping to create a very dynamic approach to these processes.

For example I also have a Process__c custom object, and with a SOQL statement I can get a list of all the Process_c records I need for a given context. These records contain the String name of a class that I want to instantiate, but for the life of me I can't seem to find a way to do this.

I've tried something like the following:

String s = 'Account';
List<Process__c> activeProcesses = [SELECT Name FROM Process__c WHERE Active__c = TRUE AND Object__c = :s];
List<String> processNames = Utils.Data.Convert.stringList(activeProcesses, 'Name');

Type t = Type.forName('Process');
List<Process> processes = new List<Process>();
for(String processName : processNames){
    Process p = t.newInstance(processName);
    processes.add(p);
}

The error I'm getting when attempting this is:

Method does not exist or incorrect signature: [Type].newInstance(String)

I really hope the harsh reality isn't that this is just not possible but if it is I need to know that as well, so any insight you have with this question would be greatly appreciated.

Best Answer

Your strategy will work, but your constructor must contain no parameters, and the same goes for your newInstance() call. You pass the name of the Type you want to construct into the Type.forName method.

Type customType = Type.forName('SomeClass');
SomeClass instance = (SomeClass)customType.newInstance();

You probably will want to implement an interface here as well. Something like:

public interface IProcess { void execute(); }
public class Process1
{
    public Process1()
    {
        // instantiation logic
    }
    public void execute()
    {
        // execution logic
    }
}

You would use the above as follows:

IProcess instance = (IProcess)Type.forName('Process1').newInstance();

You don't even really need to cache it for simple cases:

(IProcess)Type.forName('Process1').newInstance().execute();

Related Solutions

[SalesForce] How to run a batch class for list of string

All lists are iterables. Create a constructor to take the list, and change the interface of your class:

global class DF_BatchToExcessFields implements Database.Batchable<String> {...

Then return the list in the Start method. Here's a great article by AFawcett to help you get the idea:

http://andyinthecloud.com/2013/08/11/batch-worker-getting-more-done-with-less-work/

Iterable<String> i = new List<String> { 'A', 'B', 'C' };

public with sharing class SimpleBatchApex implements Database.Batchable<String> {
    public Iterable<String> start(Database.BatchableContext BC) {
        return new List<String> { 'Do something', 'Do something else', 'And something more' };
    }

    public void execute(Database.BatchableContext info, List<String> strings) {
        // Do something really expensive with the string!
        String myString = strings[0];
    }

    public void finish(Database.BatchableContext info) {}
}

then try it out in Developer Console

//Process the String's one by one each with its own governor context
Id jobId = Database.executeBatch(new SimpleBatchApex(), 1);

[SalesForce] Visualforce dynamic sObject table column value formatting

So I made a Map fieldTypeMap and a component to handle the date/datetime format

Here is what I did, maybe it will be usefull for someone else.

Controller

I added the map as an attribute of my inner class into the controller:

// header/type mapping
public Map<String,String> headerTypeMap {get;set;}

I initialize it at the end of the constructor, thanks to this.headers (array of string header/field name), after the queries, like this:

        // calculation :
        runQueries();

        // mapping
        this.headerTypeMap = new Map<String,String>();
        for(String field : this.headers){
            this.headerTypeMap.put(
                field,
                Schema.getGlobalDescribe().get(objType).getDescribe().fields.getMap().get(field).getDescribe().getType()+''
            );
        }

Visualforce component

Because I often need to format date and datetime I thought it could be a good idea to create a formating component So I made a quick and dirty one:

<apex:component controller="FormatedValueController">
<apex:attribute name="dateValue" 
    type="Date" 
    assignTo="{!inputDateValue}"
    description="input value to formatTodoBlock__c record that contains data" 
/>
<apex:attribute name="datetimeValue" 
    type="Date" 
    assignTo="{!inputDateTimeValue}"
    description="input value to formatTodoBlock__c record that contains data" 
/>

{!formatedvalue}

Controller:

public class FormatedValueController {
    public Date     inputDateValue {get;set;}
    public Datetime inputDateTimeValue {get;set;}

    public String getFormatedValue(){
        String formatedValue = '';
        formatedValue += inputDateValue == null ? '' : inputDateValue.format();
        formatedValue += inputDateTimeValue == null ? '' : inputDateTimeValue.format();
        return formatedValue;
    }
}

And a quick&dirty test class too (for code coverage only):

@isTest
global class FormatedValueController_test{
    static testMethod void FormatedValueController() {
        FormatedValueController c = new FormatedValueController();
        Test.startTest ();
        c.getFormatedValue();
        Test.stopTest();
    }
}

100% you-hou ;)

And finally ...

Main Component

Oddly I need to use "{!todoBlock.headerTypeMap[header]}" everywhere, where todoBlock is the instance of my innerclass and header the var of repeat on headers attribute (table with a dynamic number of columns).

I wanted to use an apex variable for each header, kind of:

<apex:variable var="type" value="{!todoBlock.headerTypeMap[header]}" />

but for an unknown reason it just display the last header value in every loop. For example if I have DATE, DATETIME, STRING, it displays STRING, STRING, STRING. Not a big deal to use the full code, it is just less readable.

So here it is :

<apex:outputLabel rendered="{!todoBlock.headerTypeMap[header]=='DATETIME'}">
    <c:FormatedValue datetimeValue="{!rec[header]}"/>
</apex:outputLabel>

<apex:outputLabel rendered="{!todoBlock.headerTypeMap[header]=='DATE'}">
    <c:FormatedValue dateValue="{!rec[header]}"/>
</apex:outputLabel>

<apex:outputLabel rendered="{!NOT(AND(todoBlock.headerTypeMap[header]=='DATETIME',todoBlock.headerTypeMap[header]=='DATE'))}">
    {!rec[header]}
</apex:outputLabel>

Best Answer

Related Solutions

[SalesForce] How to run a batch class for list of string

[SalesForce] Visualforce dynamic sObject table column value formatting

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