Passing objects from one page to another

dgp0961

I have created a PHP class object in one PHP page and would like to pass this object to another page and call several of the functions (methods) within the object on the second page. Whenever I refer to the object in the second page it is undefined and gives me an error.

How can I pass an object from one page to another?

Note: I have tried using globals without success and exen the session functions which give my nasty warnings with the browser.

Below is a simple code example:

file1.php

class myobj {
my class variables and functions are here.....
}

$newObj = new myobj;

file2.php

$newObj->func();

Piranha

The simple answer is that you can't do that. You have to save the variables you use in the object some way, then create a new object on the next page.

It is easier to understand why it is not possible if you think of it as a new program running every time you load a page. When the program terminates (the PHP script have created everything) the HTML page is sent and then there exist nothing from the terminated program.

Installer

You can do it like this:
Myclass.class.php

class Myclass 
{
    public $var;

function __construct()
{
    $this->var = 'Hello from ';
}

function echo_var()
{
    echo $this->var . $_SERVER['PHP_SELF'] . '<br />';
}
}

page1.php

include './Myclass.class.php';
session_start();
if (isset($_SESSION['newobj'])) {
    $newobj = $_SESSION['newobj'];
    echo 'Object passed via $_SESSION<br />'; 
} else {
    $newobj = new Myclass;
    $_SESSION['newobj'] = $newobj;
    echo 'Object created with <I>new</I><br />'; 
}
$newobj->echo_var();
echo '<a href="page2.php">Page 2</a>';

page2.php

include './Myclass.class.php';
session_start();
if (isset($_SESSION['newobj'])) {
    $newobj = $_SESSION['newobj'];
    echo 'Object passed via $_SESSION<br />'; 
} else {
    $newobj = new Myclass;
    $_SESSION['newobj'] = $newobj;
    echo 'Object created with <I>new</I><br />'; 
}
$newobj->echo_var();
echo '<a href="page1.php">Page 1</a>';

dgp0961

Thanks for your response. I actually tried this and when I call the session_start() function I get a warning message displayed in the page related to session cookies (I beleive - I'm not in front of my development PC right now). So, the session functions are creating warnings. Is this a browser setting? I am using IE 7.0 on Win XP SP2.

Installer

Try allowing cookies for your site under the "Privacy" tab of "Internet Options". Of course you'll want to have your production code cope somehow with users who also disallow cookies.

Or check your "php.ini" session settings, such as "session.use_cookies", etc. That's the best I can tell you right now. I'm going to be away, too. 🙂

dgp0961

Thanks for your reply. I discovered my problem with the warning messages from the start_session call and have resolved that. I am still having one issue with the sample code you provided.

The page1.php code works fine and it creates the $newobj and stores it in the session array. When I call the page2.php file (via the link) it displays the message 'Object passed via $_SESSION' but when the $newobj->echo_var() function is called I receive an error that the object is not valid. Any ideas?

Installer

I forgot to mention that the code was for PHP5. But apparently you're using v5, too, otherwise you would have gotten an error right away. But, after modifying it for v4 (by changing "public" to "var" and "__construct" to "Myclass") and running it on a v4 server, it all works perfectly, as it does on a v5 server with the original code. So again I'm at a loss as to why it won't for you.

BTW, what was your problem with the warning messages earlier?

dgp0961

Oh well, I'm not sure why its not working. I am using xampplite for my Apache server running locally on a Win XP SP 2 machine. Are you familiar with xampplite?
Any suggestions on how I can debug this issue?

BTW, the warning messages were occuring because I was calling the session_start() function after the HTML header information in my .php file. So, moving the session start above the header, resolved that issue.

dgp0961

Follow-up to my previous message. Below is the output I receive when the 2nd page is loaded.

Object passed via $_SESSION

Fatal error: main() [<a
href='function.main'>function.main</a>]: The script
tried to execute a method or access a property of an
incomplete object. Please ensure that the class
definition "Myclass" of the object you are
trying to operate on was loaded before unserialize()
gets called or provide a __autoload() function to load
the class definition in
C:\XAMPP\xampplite\htdocs\MyClassPage2.php on line 17

I am not calling the serialize() or unserialize() functions - should I? Maybe this will help with any suggestions someone might have. Any thoughts on how I can debug this?

NogDog

You can use serialize/unserialize something like the following. Note that you need to load the class definition before unserializing the object:

first file:

session_start();
require_once "DB.class.php";
$db = new DB(); // instanitate object
$_SESSION['db'] = serialize($db); // save serialized version of object in $_SESSION

second file:

session_start();
require_once "DB.class.php"; // load class definition first...
$db = unserialize($_SESSION['db']); // ...then unserialize the object

dgp0961

Thanks for the suggestion. I placed the serialize and unserialize functions in the code and still got an error. Something must be going on with my php.ini settings or ?.... I am sure I have coded this correctly but it is still not working. Argggggg

Installer

There should be no need to use serialize/unserialize, as both those procedures will be done automatically by PHP.

NogDog

Just to make sure, are you require()-ing the file that defines the object's class prior to the session_start()?