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PHP类中的魔术方法(Magic Method)简明总结_php实例

程序员文章站 2022-05-21 15:41:56
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1. __construct()和__destruct()

在实例被 创建/销毁 的时候被调用,都可以传递0个或多个参数。

class A
 {
  function A()
  {
   echo "build A";
  }

  function __destruct()
  {
   echo "destroy A";
  }
 }

 $obj = new A();
 //unset($obj);

Note:The destructor method will be called as soon as there are no other references to a particular object, or in any order during the shutdown sequence.

  关于构造函数,PHP5.3.3开始,一个定义在某个特定的命名空间里的class中以类名命名的方法将不再被认为是构造函数。在无命名空间的类中与原来一样依旧是构造函数。如:

namespace Foo;
class Bar {
  public function Bar() {
    // treated as constructor in PHP 5.3.0-5.3.2
    // treated as regular method as of PHP 5.3.3
  }
}

如果没有namespace Foo; 那么Bar()还将被当作构造函数。另外,如果存在下面的情况:

function __construct()
  {
   echo "construct A";
  }

  function A()
  {
   echo "build A";
  }

  function __destruct()
  {
   echo "destroy A";
  }
 }

即既包含__construct()又包含与类名同名的函数,那么将只调用__construct()。

2. __call()和__callStatic()

当尝试调用一个不存在的方法时调用该方法。两个参数,一个是方法名,一个是被调用方法的参数数组。

class MethodTest
{
  public function __call($name, $arguments)
  {
    // Note: value of $name is case sensitive.
    echo "Calling object method '$name' "
       . implode(' ', $arguments). "
"; } public static function __callStatic($name, $arguments) { // Note: value of $name is case sensitive. echo "Calling static method '$name' " . implode(' ', $arguments). "
"; } } $obj = new MethodTest; $obj->runTest('in','object','context'); MethodTest::runTest('in','static','context');

其中,$arguments作为一个array传入。运行结果:

Calling object method 'runTest' in object context
Calling static method 'runTest' in static context

还要注意函数的作用域protected和private:

class TestMagicCallMethod {
  public function foo()
  {
    echo __METHOD__.PHP_EOL."
"; } public function __call($method, $args) { echo __METHOD__.PHP_EOL."
"; if(method_exists($this, $method)) { $this->$method(); } } protected function bar() { echo __METHOD__.PHP_EOL."
"; } private function baz() { echo __METHOD__.PHP_EOL."
"; } } $test = new TestMagicCallMethod(); $test->foo(); /** * Outputs: * TestMagicCallMethod::foo */ $test->bar(); /** * Outputs: * TestMagicCallMethod::__call * TestMagicCallMethod::bar */ $test->baz(); /** * Outputs: * TestMagicCallMethod::__call * TestMagicCallMethod::baz */

3.__get()和__set()

  当试图读取一个对象并不存在的属性的时候被调用。

  Note:我们可以用这个函数实现类似java中反射的各种操作。

class Test
{
  public function __get($key)
  {
   echo $key . " not exists";
  }
  public function __set($key,$value)
  {
   echo $key . " = ".$value;
  }
}

$t = new Test();
echo $t->name."
"; $t->name = "abc";

输出:
name not exists
name = abc

4. __toString()

 这个方法类似于java的toString()方法,当我们直接打印对象的时候回调用这个函数,函数必须返回一个string。

class Test
{
  private $name = "abc";
  private $age = 12;

  public function __toString()
  {
    return "name : $this->name, age : $this->age";
  }
}

$t = new Test();
echo $t;

输出:

name : abc, age : 12