Instantiating classes and accessing methods from different classes

Question

I'm trying to use a Class_B function in one of Class_A's functions. But a lot of Class_B's functions include $this which causes problems. These are both classes (each class is of course in its own file):

class Class_A
{
   function hello()
   {
      require('class_b.php');
      echo 'Hello ' . Class_B::person();
   }

   function bye()
   {
      require('class_b.php');
      echo 'Bye ' . Class_B::person();
   }
}

class Class_B
{
   function person()
   {
      // various operations and variables
      echo $this->get_user($id);
   }
}

When I run the Class_A file I get Call to undefined method Class_A::person() in (...) because I think the $this value is changed when I instantiate the Class_A class. It overrules the Class_B value. How can I stop this?

Also, another question: how can I access Class_B from every function in Class_A? I don't want to redeclare the class. Do I need to do this:

class Class_A
{
   function function1()
   {
      require('class_b.php');
      $class_b = new Class_B();
      // code
   }

   function function2()
   {
      require('class_b.php');
      $class_b = new Class_B();
      // code
   }
}

Or do I need to use a constructor or something?

Gedrox · Accepted Answer · 2011-07-09 07:13:21Z

2

By Class_B::person() you are calling the method statically. So you should declare the person() method as static and can't use $this because you don't have an instance of Class_B.

If you need an instance of Class_B, just create it and store in the class_B on construction.

class Class_A {
  private $b;
  function __construct()
  {
    $this->b = new Class_B();
  }     
  function stuff()
  {
    $this->b->person();
  }

edited Jul 9, 2011 at 7:13

answered Jul 8, 2011 at 20:16

Gedrox

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1 Comment

hohner Over a year ago

This worked great. I tried to edit your post to add the final } but it didn't let me!

tdammers · Accepted Answer · 2011-07-08 20:15:52Z

1

Don't put require inside a method. Code in an included file inherits the scope of the place where you include it, and in your example, bad things happen. Also, for class definition scripts, consider require_once instead of require, to avoid multiple definitions.

As a rule of thumb, put all includes and requires at the top of your script. Better yet, set up a class autoloader, and register it in an auto_prepend script. That way, you won't have to manually include anything at all (at least not for class definitions).

answered Jul 8, 2011 at 20:15

tdammers

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1 Comment

The Maniac Over a year ago

Here is the documentation on auto-loading classes.

Michael Berkowski · Accepted Answer · 2011-07-08 20:16:11Z

0

What you might want is dependency injection, whereby you pass an object of Class_B into Class_A's constructor and hold it as a property in Class_A. It then becomes available in Class_A as $this->classB or similar.

// Include Class_B code outside the class.
require_once('class_b.php');
class Class_A {
  // Property to hold Class_B
  public $b;

  // Constructor
  public function __construct($b) {
    $this->b = $b;
  }

  public function function1(){
     // code
     $this->b;
  }
  public function function2(){
     // code
     $this->b;
  }
}

// Now call your objects:
// The Class_B which will be injected into A
$b = new Class_B();
// Your Class_A, which holds an instance of Class_B as a property
$a = new A($b);

answered Jul 8, 2011 at 20:16

Michael Berkowski

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