Question

I have an object of some class that obeys the singleton pattern. I need to initialize it in one file and then use it in others. I don’t know how to do this, here is what I tried :

//myClass.php
class myClass
{
    private static $instance = null;

    private function __construct($args)
    {
        //stuff
    }

    public function Create($args)
    {
        self::$instance = new myClass($args);
        return self::$instance;
    }

    public function Get()
    {
        return self::$instance;
    }
}

//index.php
<?php
require_once('myClass.php');
$instance = myClass::Create($args);
?>
<a href="test.php">Test Me!</a>

//test.php
echo(is_null(myClass::Get())); //displays 1

So the problem is that from test.php, myClass::get() always returns null!

I have also tried to store the instance in the $_SESSION, which gives me the same result. Can you please point me in the right direction?

Answer 1

You should include file with the class difinition in each file where it used (and it should be included before it will in use).

<?php // filename: test.php
include_once("myClass.php");
$oClassInstance = myClass::Get();

var_dump($oClassInstance);

BTW

You don’t need to define those two methods Create and Get. You can create only one method called getInstance:

// only one instance of the class
private static $_oInstance = null;

public static function getInstace()
{
    if (!self::$_oInstance)
    {
        self::$_oInstance = new self();
    }

    return self::$_oInstance;
}

And then you can use it like:

<?php // filename: index.php
include_once("myClass.php");

// if instance does not exist yet then it will be created and returned
$oClass = myClass::getInstace();

<?php // filename: test.php
include_once("myClass.php");

// the instance already created and stored in myClass::$_oInstance variable
// so it just will be returned
$oClass = myClass::getInstance();

UPD

If you have to put some arguments into constructor just use predefined arguments:

private function __construct($aArg)
{
    // this code will be launched once when instance is created
    // in the any other cases you'll return already created object
}

public static function getInstance($aArgs = null)
{
    if (!self::$_oInstance)
    {
        self::$_oInstance = new self($aArgs);
    }

    return self::$_oInstance;
}

ANSWER

Sorry that you have to scroll a few screens to find this =)))
The reason why you can’t use myClass::Get() in you context is that you have 2 scripts that means – two different programs.
Singleton should be used within a single application (one script).

So in your case, correct usage will be module system:
– index.php
– main.php
– test.php

// file: index.php
include_once "myClass.php"

$module = $_GET["module"];
include_once $module ".php";

// file: main.php
$oClass = myClass::Create($someArgs);
var_dump($oClass); // you'll see you class body

// file: test.php
$oClass=  myClass::Get();
var_dump($oClass); // you'll see the same class body as above

And your links will be:

• index.php?module=main
• index.php?module=test