类中的魔术方法
PHP 魔术方法指的是在某些时刻会自动被调用的内置函数，它们以两个连续的下划线开头。
类中的魔术方法
__construct()
类的构造函数，用于初始化对象，在对象实例化时自动运行
__destruct()
析构函数，用于在 php 运行终止时，释放对象所占用的内存。析构函数是 php 的垃圾回收机制，使用栈结构，后进先出。
构造函数和析构函数的例子
| 123456789101112131415161718 | class computer{ private $brand; function __construct($brand){ $this->brand = $brand; } function __destruct(){ echo "release ".$this->brand."<br>"; }} $myComputer = new computer("MAC");$yourComputer = new computer("Asus");$hisComputer = new computer("Dell"); echo "end of php file<br>"; |
输出结果如下所示
end of php filerelease Dellrelease Asusrelease MAC
可以发现析构函数在 php 文件执行结束之后才执行
__get($name)
类中用 protected 和 private 关键字定义的成员属性或方法是无法通过对象的实例访问的。__get() 方法会且仅会在对象的实例访问 proctected 和 private 成员属性 时自动执行 (访问成员方法时不会，因为没有意义)。
__get() 方法的意义在于将 proctected 和 private 成员属性进行处理后输出。
__get() 有且仅有一个输入参数
__get() 方法的一个例子
class computer{ private $brand; protected $owner; public $price; function __construct($brand, $owner, $price){ $this->brand = $brand; $this->owner = $owner; $this->price = $price; } function __get($name){ echo "It's up to me to decide if let you konw the owner and the brand of this computer or not :)<br>"; echo "I will tell you the name of woner: ".$this->owner."<br>"; echo "I won't tell you that the brand is ".md5($this->brand)."<br>"; echo "<br>"; } function __destruct(){ echo "release ".$this->brand."<br>"; } } $myComputer = new computer("MAC", "me", "1000");$yourComputer = new computer("Asus", "you", "500");$hisComputer = new computer("Dell", "his", "700"); echo $myComputer->price; echo "<br><br>"; echo $myComputer->owner;echo $yourComputer->brand; echo "end of php file<br>"; |
输出如下
1000It's up to me to decide if let you konw the owner and the brand of this computer or not :)I will tell you the name of woner: meI won't tell you that the brand is 2e25c285356cbb0ed8785a1377027d79It's up to me to decide if let you konw the owner and the brand of this computer or not :)I will tell you the name of woner: youI won't tell you that the brand is cb6ab3315634a1e4d11b091ba48b60baend of php filerelease Dellrelease Asusrelease MAC
可以看到，当访问 public 成员属性 price 时，__get()方法并没有被调用。输出 brand 时，我们使用了 md5 对其进行了加密处理，这种对封装的成员属性进行处理后输出的用法就是 get 方法的意义所在。
__set($name, $value)
__set($name, $value) 与用于给当前类中封装的方法或属性进行重新赋值或定义。
与 get 类似但不同的时，__set($name, $value)会在成员属性被访问赋值时自动执行，其中 $name 是被访问的成员属性名，$value 为成员属性被赋予的值
__set() 的例子
class computer{ private $brand; protected $owner; function __construct($brand, $owner, $price){ $this->brand = $brand; $this->owner = $owner; $this->price = $price; } function __get($name){ echo "It's up to me to decide if let you konw the owner and the brand of this computer or not :)<br>"; echo "I will tell you the name of woner: ".$this->owner."<br>"; echo "I won't tell you that the brand is ".md5($this->brand)."<br>"; echo "<br>"; } function __set($name, $value){ $this->owner = $value; echo "set $name to $value"."<br><br>"; } function __destruct(){ echo "release ".$this->brand."<br>"; } } $myComputer = new computer("MAC", "me", "1000"); echo $myComputer->owner = "my friend";echo $myComputer->owner; echo "end of php file<br>"; |
输出结果
set owner to my friendmy friendIt's up to me to decide if let you konw the owner and the brand of this computer or not :)I will tell you the name of woner: my friendI won't tell you that the brand is 2e25c285356cbb0ed8785a1377027d79end of php filerelease MAC
我们看到在给 owner 赋值时调用了 set , 而访问属性时，调用了 get 。
__tostring()
用于直接打印对象句柄，也就是说当我们使用 echo 加对象名时，__torsring()将会被自动调用
__tosring() 例子
| 123456789 | class computer{ function __tostring(){ return "This is a computer class"; }} $myComputer = new computer();echo $myComputer; |
如果没有 __totring() 方法，我们是无法使用 echo+对象名，会出现 fatal error
__call($method, $arguments)
当我们调用不存在的方法时，__call() 会自动执行，用于进行异常处理，并使程序继续正常运行。
__call() 例子
class computer{ function start(){ echo "starting computer<br>"; } function __call($m, $a){ echo "erro function: ".$m; echo "<br>"; echo "error param: "; print_r($a); echo "<br>"; }} $myComputer = new computer(); $myComputer->start();$myComputer->shutdown('10 min', '20 min');echo "here"; |
输出结果为
starting computererro function: shutdownerror param: Array ( [0] => 10 min [1] => 20 min ) here
我们可以看到，$method 返回了错误的函数名，而 arguments 返回了参数，最后输出了 "here" 说明程序继续正常运行。
__clone() 方法 和 clone 关键字
clone 关键字用于复制对象，__clone() 方法实在克隆对象时自动调用的函数
clone 例子
class computer{ public $name; function __clone(){ echo "A computer has been cloned<br>"; }} $myComputer = new computer(); $youComputer = $myComputer;$youComputer->name = 'pc1';echo "My computer's name is ".$myComputer->name."<br>";echo "<br>"; $hisComputer = clone $myComputer;$hisComputer->name = 'pc2';echo "My computer's name is ".$myComputer->name."<br>";echo "His computer's name is ".$hisComputer->name."<br>"; |
输出结果
My computer's name is pc1A computer has been clonedMy computer's name is pc1His computer's name is pc2
我们看到用 = 号并不能复制对象，只是为对象添加了一个别名而已，这里 $myComputer 和 $youComputer 指向同一块内存，修改了 $youComputer 的值相当于修改了 $myComputer 的值。
__autolaod()
在实例化对象时，__autolaod() 会自动被调用，用于快速取得对应的类文件
__autoload() 例子
<?phpfunction __autoload($class_name) { include $class_name . '.php';} $obj = new MyClass1();$obj2 = new MyClass2(); ?> |
摘自PHP手册
带 try, catch 异常处理的例子
function __autoload($class_name){ echo "want to load ".$class_name."<br>"; if(file_exists($class_name.".class.php")){ include($class_name.".class.php"); }else{ throw new Exception("Unable to laod ".$class_name.".class.php"); }} try{ $obj = new myClass();} catch(Exception $e){ echo $e->getMessage()."<br>";} |
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