PHP子类访问父变量问题

Question

我上了这门课：

Class Username {
protected $id;
protected $username;
protected $contact_information;

     private __construct($id) {
       $this->id = (int) $id; // Forces it to be a string
       $contact_information = new ContactInformation($this->id);
     }
}

Class ContactInformation extends Username {
    protected $mobile;
    protected $email;
    protected $nextel_id;
    .....
}

我的问题是：我想访问 ContactInformation 上的 $id 和 $username（以及许多其他变量），但是 parent:: 或 $this-> 不起作用，看起来就像每次我执行“new ContactInformation.. ..) PHP 创建一个“新用户名”。有机会从用户名访问当前值吗？

谢谢

Answer 1

为什么用户名构造函数是私有的？如果您想让创建用户名成为不可能，请将用户名类抽象化。另外，不要从父类中创建新的联系信息。这是另一种说法：

abstract class Username {
   protected $id;
   protected $username;

   public __construct($id) {
      $this->id = (int) $id; // Forces it to be a string
   }
}

class ContactInformation extends Username {
    protected $mobile;
    protected $email;
    protected $nextel_id;
    public __construct($id, $mobile, $email, $nextel_id) {
       parent::__construct($id)
       $this->mobile = $mobile;
       ....
    }
}

现在，不是直接实例化用户名（现在不可能），而是创建一个 ContactInformation。 ContactInformation 然后在它自己的构造函数中调用 Username 构造函数。

Answer 2

parent:: 方法仅用于访问您在子类中重写的父方法，或静态变量，例如：

class Base
{
    protected static $me;

    public function __construct ()
    {
        self::$me = 'the base';
    }

    public function who() {
        echo self::$me;
    }
}

class Child extends Base
{
    protected static $me;

    public function __construct ()
    {
        parent::__construct();
        self::$me = 'the child extends '.parent::$me;
    }

    // until PHP 5.3, will need to redeclare this
    public function who() {
        echo self::$me;
    }
}

$objA = new Base;
$objA->who(); // "the base"

$objB = new Child;
$objB->who(); // "the child extends the base"

你可能想要一个合适的子类。不要在基类的构造函数中创建子类，这会颠倒各种 OOP 最佳实践（松散耦合等），同时还会创建无限循环。 （new ContactInformation() 调用 Username 构造函数，该构造函数创建一个 new ContactInformation() ...）。

如果你想要一个子类，像这样：

/**
 * Stores basic user information
 */
class User
{
    protected $id;
    protected $username;

    // You could make this protected if you only wanted
    // the subclasses to be instantiated
    public function __construct ( $id )
    {
        $this->id = (int)$id; // cast to INT, not string

        // probably find the username, right?
    }
}

/**
 * Access to a user's contact information
 */
class ContactInformation extends User
{
    protected $mobile;
    protected $email;
    protected $nextel;

    // We're overriding the constructor...
    public function __construct ( $id )
    {
        // ... so we need to call the parent's
        // constructor.
        parent::__construct($id);

        // fetch the additional contact information
    }
}

或者您可以使用委托，但 ContactInformation 方法将无法直接访问用户名属性。

class Username
{
    protected $id;
    protected $contact_information;

    public function __construct($id)
    {
        $this->id = (int)$id;
        $this->contact_information = new ContactInformation($this->id);
    }
}

class ContactInformation // no inheritance here!
{
    protected $user_id;
    protected $mobile;

    public function __construct($id)
    {
        $this->user_id = (int)$id;
        // and so on
    }
}

Answer 3

首先，当您创建ContactInformation 时，它还包含Username 的所有非私有属性和方法。您不需要单独的 Username 实例。

Class Username {
    protected $id;
    protected $username;

    protected __construct($id) {
        $this->id = (int) $id; // Forces it to be a string
    }
}

Class ContactInformation extends Username {
    protected $mobile;
    protected $email;
    protected $nextel_id;
    // Pretend that these are here because they're defined in my parent
    //protected $id;
    //protected $username;

    public __construct($id) {
        parent::__construct($id);
        echo $this->id; //Should echo 1
    }
}

但是，由于所有字段都受到保护，因此这是行不通的：

$contact_information = new ContactInformation(1); // Works fine
echo $contact_information->id;
// Whoops, visibility error because id isn't public

Answer 4

如果我对您的理解正确，您想从该对象中包含的对象访问该对象的属性吗？如果这是正确的，那么它是如何完成的：

class A {

  // These are the properties you want to access from the child object
  public $property_a;
  public $property_b;
  public $property_c;

  // This is the child object variable
  public $child_object;

  public function __construct( ) {

    // Pass 'this' into the child so that the child has a reference back to the parent
    $this->child_object = new B($this);
  }
}

class B {

  // Holds a reference to the parent object
  protected $parent_object;

  public function __construct( $object ) {

    // Remember the reference to the parent object
    $this->parent_object = $object;
  }

  // Just a Demonstration Method
  public print_parent_property_a()
  {
    // Reach into the referred parent object, and get it's property
    print $this->parent_object->property_a;
  }
}

如果你这样做：

$my_object = new A();
$my_object->property_a = 'test_value';
$my_object->child_object->print_parent_property_a();

你会得到'test_value'

这与您的示例略有不同，因为您需要将父类属性公开，以便子类可以访问它们。

这一切都行得通，因为在 PHP 中，对象总是通过引用传递，除非您明确克隆它们。

Answer 5

<?php

 abstract class employee
{ 
    //create member variable in parent class

    protected $name;
    protected $id;
    protected $mobile;  

    //constructor of parent class 
    public function __construct($n , $i , $m)
    {
        $this->name=$n;
        $this->id=$i;
        $this->mobile=$m;
    }
    //create method will return name
    public function ShowFullName()
    {

        return $this->name;
    }
//create method will return contact
    public function ShowContact()
    {

        return $this->mobile;
    }

}

class FulltimeEmployee extends employee
{

    private $days;
    private $salary;



        //create child constructor 
    public function __construct($n , $i , $mo , $d , $s)
    {
        $this->days=$d;
        $this->salary=$s;

        //calling parent constructor now we can use parent class member while calling child class constructor
        parent::__construct($n , $i , $mo);
    }

    public function calculate()
    {

        return $this->salary * $this->days;

    }
}

//providing data to child class constructor including parent class values
$child = new FulltimeEmployee("james",120,9033474118 , 2 , 200);
echo $child->calculate();
echo $child->ShowFullName();