php面向对象类中常用的魔术方法

1、__construct():构造方法，当类被实例化new $class时被自动调用的方法，在类的继承中可以继承与覆盖该方法，例：

//__construct()
class construct{
    public function __construct(){
        $this->var = "this is var";    
    }
}
class con2 extends construct{
    public function __construct(){
        $this->var = "this is var2";    
    }
}
$con2 = new con2;
echo $con2->var;

3、__destruct():当对象销毁或者不再使用时(页面运行完)，自动调用这个方法，例：

class construct{
    public function __construct(){
        $this->var = "this is var";    
    }
    public function __destruct(){
        echo 'close';    
    }
}
$con = new construct;
//或者最常用的关闭资源
class destruct{
    public function __construct(){
        $this->logfile_handle = fopen('/tmp/log.txt',w);    
    }
    public function __destruct(){
        fclose($this->logfile_handle);    
    }
}

4、__toString():该方法用于一个类被当成字符串时应怎么样回应，也就是echo $class时返回的内容是什么，如果没有__toString()魔术方法时，将会返回一个E_RECOVERABLE_ERROR级别的致命错误。

例：

<?php
class TestClass{
    public $foo;
    public function __construct($foo){
        $this->foo = $foo;    
    }
    public function __toString(){
        return $this->foo;
    }
    
}
$class = new TestClass('Hello');
echo $class;//Hello
?>

5、__invoke():该魔术方法用于类被当作函数使用时，自动调用该方法，但是...__invoke()魔术方法只在PHP5.3.0以上才有效；例

//__invoke() PHP5.3.0以上版本有效
class CallableClass{
    function __invoke($x){
        var_dump($x);    
    }
}
$obj = new CallableClass;
$obj(5);
var_dump(is_callable($obj));//true

6、__get()与__set():从一个难以访问的属性读取数据是自动调用__get()魔术方法，从一个难以访问的熟悉赋值的时候自动调用__set()魔术方法，难以访问包括（私有属性，未定义属性、没有初始化的属性）例：

//__get()  __set()
class demoClass{
    private $a;
    private function __get($name){
        return 'this var not exist';
    }
    private function __set($name,$value){
        echo 'this var value not exist';    
    }
}
$demo = new demoClass();
var_dump($demo->a);//调用__get()方法
$demo->a = 1;//调用__set()方法

7、__call():该方法在范围类中不存在的方法时自动调用的方法，参数有两个；例：

//__call()
class funClass{
    public function __call($name,$arg){
        echo $name.'function not exist';    
    }
}
$fun = new funClass();
$fun->aa();//function not exist

8、__sleep()和__wakeup:这两个魔术方法是在对象序列化serialize()和解序列化unserialize()自动调用的方法：例

//__sleep __wakeup 简单实例
class sleepClass{
    public $myContent;
    public function __construct($string){
        $this->myContent = $string;    
    }
    public function __sleep(){
        $this->myContent = "this is mimi";
        return array('myContent');
    }
    public function __wakeup(){
        echo 'aaa';    
    }
}
$sleep = new sleepClass('i love bb');
$ser = serialize($sleep);//this is mimi
unserialize($ser);//aaa
//或者 常用实例
class Connection {
    protected $link;
    private $server, $username, $password, $db;
    public function __construct($server, $username, $password, $db)
    {
        $this->server = $server;
        $this->username = $username;
        $this->password = $password;
        $this->db = $db;
        $this->connect();
    }
    private function connect()
    {
        $this->link = mysql_connect($this->server, $this->username, $this->password);
        mysql_select_db($this->db, $this->link);
    }
    public function __sleep()
    {
        return array('server', 'username', 'password', 'db');
    }
    public function __wakeup()
    {
        $this->connect();
    }
}
$con = new Connection('127.0.0.1','root','','mythinkcom');
echo serialize($con);

9、__clone():$obj2 = clone $obj1与$obj2 = $obj1的区别是前者有两块内存地址，而后者只有一块内存地址。

class cloneClass{
    public $var = 'aa';    
}
$clone = new cloneClass;
$clone2 = clone $clone;
echo $clone->var;
echo $clone2->var;