Home Backend Development PHP Tutorial Detailed explanation of magic method examples in OOP

Detailed explanation of magic method examples in OOP

Jun 15, 2017 pm 02:18 PM
php php magic method

本篇文章主要介绍了浅谈PHP中的面向对象OOP中的魔术方法 ,具有一定的参考价值,感兴趣的小伙伴们可以参考一下

一、什么是魔术方法:

PHP为我们提供了一系列用__开头的函数,这些函数无需自己手动调用,会在合适的时机自动调用,这类函数称为魔术函数。
例如:

function __construct(){} 在new一个新对象时自动调用此函数

二、PHP中都有那些魔术方法,以及它们的作用:

1.__construct():构造函数,new对象时自动调用

eg:


class Person{
    public $name;
    public $age;
    
    function __construct($name,$age){
      $this->name=$name;
      $this->age=$age;
    }
}
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在new新的Person对象时会自动调用__construct()函数,将传入的参数分别赋给$name,$age。

2.__destruct():析构函数,当一个对象被销毁前自动调用


class Person{
    public $name;
    public $age;
    
    function __destruct(){
    echo "这个对象被销毁了";
  }
}
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同上所述,对象被销毁时执行此魔术方法

3.__get():访问类中私有属性时自动调用,传递读取属性名,返回$this->属性名


class Person{
    private $name;
    public $age;
    
    function __get($name){
     return $this->$name;
    }
}
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如上代码,$name被设为私有属性后不能直接通过$this->name;的方式读取,因此需要设置__get()魔术方法来读取。

4.__set():给类的私有属性赋值时自动调用,传递需设置的属性名,属性值


class Person{
    private $name;
    public $age;
    
    function __set($key,$value){
      $this->$key=$value;
    }
}
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同__get()方法,私有属性不能通过$this->name="aaa";的方式直接设置,需要设置__set()方法,传入的参数分别是属性名和属性值。

5.__isset():使用isset检测对象私有属性时调用,传递检测的属性名,返回isset($this->属性名)


class Person{
    private $name;
    public $age;
    
    function __isset($name){
    return isset($this->$name);
  }
}
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使用isset检测对象私有属性时调用,其他同上。

6.__unset():使用unset()函数删除对象私有属性时调用,传递删除的属性名,方法中执行unset($this->属性名)


class Person{
    private $name;
    public $age;
    
    function __unset($name){
      unset($this->$name);
    }
}
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同上,在用unset()函数删除私有属性时调用。

7.__toString():使用echo打印对象时调用,返回打印对象时想要显示的内容,返回必须是字符串


class Person{
    public $name;
    public $age;
    
    function __toString(){
      $str = <<<str
      您要打印的内容是:<br>
      \$name=>{$this->name};<br>
      \$age=>{$this->age};<br>
str;
      return $str;
    }
}
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使用echo打印对象时调用,返回打印对象时想要显示的内容。

8.__call():调用一个类中未定义的或未公开的方法时自动调用,传递被调用的函数名及参数列表


class Person{
    public $name;
    public $age;
    
    function __call($funcName,$funcParams){
      echo "您调用的函数{$funcName},参数列表";
      print_r($funcParams);
      echo "不存在/未公开";
    }
}
$zhangsan=new Person();
$zhangsan->say(1,2,3);
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如代码所示,调用不存在的say(1,2,3);时,会打印

您调用的函数way,参数列表Array ( [0] => 123 ) 不存在

9.__clone():当使用clone关键字,克隆一个对象时自动调用,作用是为新克隆的对象初始化赋值


class Person{
    public $name;
    public $age;
    
    function __clone(){
    $this->name="lisi";
    }
}  
$zhangsan=new Person("zhangsan",24);
$lisi=clone $zhangsan;
echo $lisi->name;
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打印出的结果是"lisi",而不是"zhangsan"。

10.__sleep():对象序列化时自动调用,返回一个数组,数组中的值就是可以序列化的属性


class Person{
    public $name;
    public $age;
    
   function __sleep(){
    return array("name","age");
  }
}
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如上述代码,在用serialize()序列化对象时只有"name","age"属性会被序列化。

11.__wakeup():对象反序列化时自动调用,为反序列化新产生的对象进行初始化赋值


class Person{
    public $name;
    public $age;
    
   function __wakeup(){
    $this -> name = "lisi";
  }
}
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将对象序列化后再反序列化,同时给对象的name属性赋初值为"lisi"。

12.__autolode():需要在类外部声明函数,当实例化一个未声明的类时自动调用,传递实例化的类名,可以使用类名自动加载对应的类文件。


function __autoload($className){
  include "class/".strtolower($className).".class.php";
}
  
$zhangsan=new Person();
$zhangsan->say();
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如上述代码,Person类不存在时调用__autolode()方法,载入写在文件外的类,"class/".strtolower($className).".class.php";就是类文件的相对路径,$className就是

不在本文件中的类的类名,因此在创建外部类文件时命名方式必须是小写的类名.class.php。__autolode()方法也是惟一一个不用写在类中的魔术方法。

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