1. __toString: 當對象被打印時，如果該類定義了該方法，則打印該方法的返回值，否則將按照PHP的缺省行為輸出打印結果。該方法類似於Java中的toString()。 復制代碼 <?php class TestClass { public function __toString() { return "This is TestClass::__toString.\n"; } } $testObj = new TestClass(); print $testObj; 復制代碼 運行結果如下： Stephens-Air:Desktop$ php Test.php This is TestClass::__toString. 2. __get和__set: 這兩個方法用於處理類中未聲明的屬性訪問。當對象使用者試圖訪問未聲明的對象屬性時，__get()會被調用，並帶有一個包含要訪問的屬性名稱字符串作為參數。無論從__get()方法返回什麼，都會直接返回給調用者，就如同帶有該值的屬性存在一樣。另外需要注意的是，如果屬性存在，但是其訪問可見性為private或protected，那麼這兩個攔截方法同樣會被調用，反之，如果屬性存在切可訪問，那麼直接訪問屬性即可，這兩個方法將不再會被調用。以下為__get()攔截方法的示例代碼： 復制代碼 <?php class TestClass { private $privateField; public $publicField; public function __construct() { $this->privateField = "This is a private Field.\n"; $this->publicField = "This is a public Field.\n"; } public function __get($property) { print "__get() is called.\n"; $method = "get${property}"; if (method_exists($this, $method)) { return $this->$method(); } return "This is undefined field.\n"; } public function getPrivateField() { return $this->privateField; } } $testObj = new TestClass(); print $testObj->privateField; print $testObj->undefinedField; print $testObj->publicField; 復制代碼 運行結果如下： Stephens-Air:Desktop$ php Test.php __get() is called. This is a private Field. __get() is called. This is undefined field. This is a public Field. __set()方法被調用的規則和__get()基本相同，差別是用於攔截未定義或不可見類屬性的賦值操作。另外，該方法接收兩個參數，分別是屬性名稱和要設定的值。見如下代碼示例： 復制代碼 <?php class TestClass { private $privateField; public $publicField; public function __construct() { $this->privateField = "This is a private Field.\n"; $this->publicField = "This is a public Field.\n"; } public function __get($property) { print "__get() is called.\n"; $method = "get${property}"; if (method_exists($this, $method)) { return $this->$method(); } return "This is an undefined field.\n"; } public function __set($property, $value) { print "__set is called.\n"; $method = "set${property}"; if (method_exists($this, $method)) { $this->$method($value); } else { print "This is an undefined field.\n"; } } public function getPrivateField() { return $this->privateField; } public function setPrivateField($value) { $this->privateField = $value; } } $testObj = new TestClass(); $testObj->privateField = "This is a private Field after set.\n"; $testObj->undefinedField = "This is a undefined Field after set.\n"; $testObj->publicField = "This is a public Field after set.\n"; print $testObj->privateField; print $testObj->undefinedField; print $testObj->publicField; 復制代碼 運行結果如下： 復制代碼 Stephens-Air:Desktop$ php Test.php __set is called. __set is called. This is an undefined field. __get() is called. This is a private Field after set. __get() is called. This is an undefined field. This is a public Field after set. 復制代碼 3. __isset和__unset: 這兩個攔截方法被調用的規則和__get()和__set()非常類似，只是用於類中不存在或不可見屬性被isset()和unset()兩個全局方法應用時才會被分別觸發。 復制代碼 <?php class TestClass { private $privateField; public $publicField; public function __construct() { $this->privateField = "Defined private field"; $this->publicField = "Defined public field"; } public function __isset($property) { print "__isset is called.\n"; return isset($this->$property); } public function __unset($property) { print "__unset is called.\n"; if (isset($this->$property)) { unset($this->$property); } } } $testObj = new TestClass(); print 'isset($testObj->privateField) is '.(isset($testObj->privateField) ? "true" : "false")."\n"; print 'isset($testObj->undefinedField) is '.(isset($testObj->undefinedField) ? "true" : "false")."\n"; print 'isset($testObj->publicField) is '.(isset($testObj->publicField) ? "true" : "false")."\n"; print "After unset......\n"; //下面兩個函數調用後，$testObj的兩個對象屬性均會變為不可用。 //另外從輸出結果來看，__unset方法僅僅被調用一次，因為publicField為可見屬性，所以__unset不會因該屬性而被調用。 unset($testObj->privateField); unset($testObj->publicField); print 'isset($testObj->privateField) is '.(isset($testObj->privateField) ? "true" : "false")."\n"; print 'isset($testObj->publicField) is '.(isset($testObj->publicField) ? "true" : "false")."\n"; 復制代碼 運行結果如下： 復制代碼 Stephens-Air:Desktop$ php Test.php __isset is called. isset($testObj->privateField) is true __isset is called. isset($testObj->undefinedField) is false isset($testObj->publicField) is true After unset...... __unset is called. __isset is called. isset($testObj->privateField) is false __isset is called. isset($testObj->publicField) is false 復制代碼 4. __call: __call()方法是一個非常有用但又非常容易被濫用的攔截方法。當對象使用者試圖訪問當前對象未定義的成員函數時，__call()會被自動調用，同時傳遞兩個參數，分別為函數名稱和傳遞給調用函數的所有參數(數組)。__call方法返回的任何值都會返回給函數調用者，就如同該成員函數真實存在一樣。下面給出一個非常有用的委托示例。 復制代碼 <?php class DelegateClass { function printMessage($arg1, $arg2) { print "DelegateClass:delegatedMethod is called.\n"; print '$arg1 = '.$arg1.'and $arg2 = '.$arg2."\n"; } } class TestClass { private $delegateObj; public function __construct() { $this->delegateObj = new DelegateClass(); } public function __call($method, $args) { $this->delegateObj->$method($args[0],$args[1]); } } $testObj = new TestClass(); $testObj->printMessage("hello","world"); 復制代碼 運行結果如下： Stephens-Air:Desktop$ php Test.php DelegateClass:delegatedMethod is called. $arg1 = helloand $arg2 = world 從以上示例可以看出，TestClass並未聲明printMessage成員方法，但是通過__call()方法的巧妙橋接直接傳遞給了委托對象。個人認為該技巧為雙刃劍，切勿過度使用。 5. 回調函數： 回調函數的應用場景無須多述，在C/C++中充斥著無數的回調函數典型用例。 這裡只是簡單給出PHP中回調函數的使用規則。見如下示例代碼和關鍵性注釋： 復制代碼 <?php class Product { public $name; public $price; public function __construct($name, $price) { $this->name = $name; $this->price = $price; } } class ProcessSale { private $callbacks; function registerCallback($cb) { if (!is_callable($cb)) { throw new Exception("callback not callable."); } $this->callbacks[] = $cb; } function sale($product) { print "{$product->name}: processing \n"; foreach ($this->callbacks as $cb) { //以下兩種調用方式均可。 call_user_func($cb, $product); $cb($product); } } } $logger = function($product) { print " logging ({$product->name})\n"; }; $processor = new ProcessSale(); $processor->registerCallback($logger); $processor->sale(new Product("shoes",6)); print "\n"; $processor->sale(new Product("coffee",6)); 復制代碼 運行結果如下： 復制代碼 Stephens-Air:Desktop$ php Test.php shoes: processing logging (shoes) logging (shoes) coffee: processing logging (coffee) logging (coffee) 復制代碼 6. use(閉包): 在Javascript中存在大量的閉包應用，PHP中的閉包則是通過use關鍵字來完成的。對於閉包這個概念本身而言，簡要的說就是函數內的代碼可以訪問其父作用域中的變量。見如下示例代碼和關鍵性注釋： 復制代碼 <?php class Product { public $name; public $price; public function __construct($name, $price) { $this->name = $name; $this->price = $price; } } class ProcessSale { private $callbacks; function registerCallback($cb) { if (!is_callable($cb)) { throw new Exception("callback not callable."); } $this->callbacks[] = $cb; } function sale($product) { print "{$product->name}: processing \n"; foreach ($this->callbacks as $cb) { $cb($product); } } } class Totalizer { static function warnAmount($amt) { $count = 0; //注意這裡的$amt和$count均為閉包變量，其中&$count是以引用的形式傳遞的，即一旦函數內部修改了該變量的值， //那麼下次再訪問該閉包變量時，$count將為之前調用中修改後的值。 return function($product) use($amt, &$count) { $count += $product->price; print " count: $count\n"; if ($count > $amt) { print " high price reached: {$count}\n"; } }; } } $processor = new ProcessSale(); $processor->registerCallback(Totalizer::warnAmount(8)); $processor->sale(new Product("shoes",6)); $processor->sale(new Product("coffee",6)); 復制代碼 運行結果如下： shoes: processing count: 6 coffee: processing count: 12 high price reached: 12 注：該Blog中記錄的知識點，是在我學習PHP的過程中，遇到的一些PHP和其他面向對象語言相比比較獨特的地方，或者是對我本人而言確實需要簿記下來以備後查的知識點。雖然談不上什麼深度，但是還是希望能與大家分享。
