My class function is performed twice - php

Question

<?php
/*
* class: C_QUESTION_MULTIPLE_CHOICE_SINGLE_ANSWER
* properties:
* functions:
*/
class C_QUESTION_MULTIPLE_CHOICE_SINGLE_ANSWER extends C_QUESTION {
protected $q_type = 'T_MULTIPLE_CHOICE_SINGLE_ANSWER';
protected $q_type_info;
/*
* $choices:
* choices['A'] = array(answer = 'Y', description = '')
* choices['B'] = array(answer = 'N', description = '')
*/
protected $choices;
public $output_info = '';
public $count = 0;
function __construct($q_content, $option = 'load') {
// call parent's construct function to handle question base class information
// in parent construct function, it will call parent's load or save function by itself.
parent::__construct($q_content, $option);
if (! $this->op_status) {
// call function failed
return;
}
// handle multiple choice part
switch ($option) {
case 'save':
// $option = false, don't call parent::save() function
// parent construct function will call parent save function
$this->save($q_content, false);
break;
}
} // end of construct function
function save($q_content, $option = true) {
$this->count++;
$this->output_info .= '</br>'.$this->count.'</br>';
} // end of save function
}
In the above code, the sub-class function save is performed twice. If I don't call parent construct function:
/* don't call parent construct function
parent::__construct($q_content, $option);
if (! $this->op_status) {
// call function failed
return;
}
*/
The function save() will be performed once.
In the parent construct function, the parent class QUESTION will cal it's own save() function. The sub-class C_QUESTION_MULTIPLE_CHOICE_SINGLE_ANSWER override the parent function save(). So in the sub-class construction function, I manually call parent::__construct() function. But I don't why the sub-class save() function is called twice. I debug this by sub-class properties
public $output_info = '';
public $count = 0;
Please help me.
Thanks a lot.
=========================================================================================
I debuged several times after post the above question, found:
parent class QUESTION: __construct() function:
function __construct($q_content, $option = 'load') {
// set the operation status to true. If this operation fails, this will be set to false
$this->op_status = true;
switch ($option) {
case 'load':
if (!$q_content['qid']) {
$this->op_status = false;
drupal_set_message(t('question id :qid not exist. Please contact site administrator!', array(':qid' => $q_content['qid'])), 'error');
break;
}
$this->basic['qid'] = $this->extra['qid'] = $q_content['qid'];
$this->load($this->basic['qid']);
break;
case 'save':
**//$this->save($q_content);
self::save($q_content);**
break;
}
}
if I use $this->save to call parent itself save function, this statement not only call parent::save function, but also will call sub class::save function. It's very funny and confuse.
If I use self::save statement in the parent class QUESTION, then it won't call sub class::save function.
My question is, since I've already overrided parent::save function in the sub class, I should call parent::save, then call $this->save in the sub-class do something for subclass. Why when I call parent::save, it will perform both parent::save and sub-class::save. It really confuse me.
I tried to find answer in the php manual and internet, but I didn't find the relevant article can make me clear. They only say, self::function() is used for the static member function, and $this->function() is used for other member and function. But my function and member are not static. Or the default function and member are static?
Really appreciate for who can help me.
Thanks a lot.

Answer 1

In php OOP, $this-> referrer to the current instant of the class, whereas self:: referrer to the class where self:: is declared.self:: is also use to referrer to static functions and properties.
So, in your case, you have to change the call to your parent's save() function as self::save() within the parent's construct function.
Also, within your child class, you can call $this->save() to call the save function of the child, because you are overriding the parent's save function.you can also use self::save() within the child class.if you want to call parent's save function from a child class then you can use parent::save() in your child class.
No, default functions aren't static.to make them static you have to add static keyword in front of the function declaration.note that you can't declare __construct(),__deconstruct() as static.
Since your functions aren't static, when you referrer to them as self:: you are referring to the current class.it's called Scope Resolution Operator (::). also read this SO answer