本篇接續上篇PHP-物件導向(OOP)介紹-Part1

五.魔術函數(Magic Methods)

PHP提供了數個魔術函數讓操作物件(Object)變得更簡單，魔術函數會在物件發生特定行為時被呼叫，
這讓開發者更容易達成某些有用的任務，以下帶大家看幾個例子。

1.__Constructor

當一個物件被建立時，它經常需要做一些初始化，construct():是當一個物件被建立的時候會被呼叫。

以下為增加一個construct()到 MyClass，讓MyClass被實例化的時候丟出一段訊息

<?php
class MyClass
{
    public $prop1 = "I'm a class property!";

    public function __construct()          //物件被建立時呼叫訊息
    {
        echo 'The class "' . __CLASS__ . '" was initiated!<br />';
    }

    public function setProperty($newval)
    {
        $this->prop1 = $newval;
    }

    public function getProperty()
    {
        return $this->prop1 . "<br />";
    }
}

$obj = new MyClass;                       //建立新物件。

echo $obj->getProperty();                 //呼叫物件到`getProperty()`。

echo "End of file.<br />";                //結束時丟出訊息`End of file.`。

輸出到畫面會顯示

The class "MyClass" was initiated!
I'm a class property!
End of file.

2.__Destructors

而當物件被摧毀的時候，destruct():當一個物件被摧毀的時候會被呼叫。

增加一個destruct()到MyClass，讓MyClass被摧毀時的時候，丟出一段訊息

<?php
class MyClass
    {
    public $prop1 = "I'm a class property!";

    public function __construct()          //物件被建立時呼叫訊息
    {
        echo 'The class "', __CLASS__, '" was initiated!<br />';
    }

    public function __destruct()           //物件被結束時呼叫訊息
    {
        echo 'The class "', __CLASS__, '" was destroyed.<br />';
    }

    public function setProperty($newval)
    {
        $this->prop1 = $newval;
    }

    public function getProperty()
    {
        return $this->prop1 . "<br />";
    }
}

$obj = new MyClass;                       //建立新物件。

echo $obj->getProperty();                 //呼叫物件到`getProperty()`。

echo "End of file.<br />";                //結束時丟出訊息`End of file.`。

輸出到畫面會顯示

The class "MyClass" was initiated!
I'm a class property!
End of file.
The class "MyClass" was destroyed.

3.__toString

toString():避免程式試圖將MyClass當作字串輸出到瀏覽器上(被當作字串處理時觸發)，
如果把物件當作字串處理的話，在PHP中會出現無法轉換型態的錯誤

<?php
class MyClass
{
    public $prop1 = "I'm a class property!";

    public function __construct()          //物件被建立時呼叫訊息。
    {
        echo 'The class "', __CLASS__, '" was initiated!<br />';
    }

    public function __destruct()           //物件被結束時呼叫訊息。
    {
        echo 'The class "', __CLASS__, '" was destroyed.<br />';
    }

    public function __toString()           //將物件轉換為字串。
    {
        echo "Using the toString method: ";
        return $this->getProperty();
    }

    public function setProperty($newval)
    {
        $this->prop1 = $newval;
    }

    public function getProperty()
    {
        return $this->prop1 . "<br />";
    }
}

$obj = new MyClass;                       //建立新物件。

echo $obj;                                //呼叫已被轉為字串的物件。

echo "End of file.<br />";                //結束時丟出訊息`End of file.`。

輸出到畫面會顯示

The class "MyClass" was initiated!
Using the toString method: I'm a class property!
End of file.
The class "MyClass" was destroyed.

當然除了本篇提到的三個魔術函數以外，還有更多魔數函數可以在PHP : Magic Methods可以學習，
本篇介紹到此，下次見～