迭代器模式是一種行為型模式，它是一種最簡(jiǎn)單也最常見(jiàn)的設(shè)計(jì)模式。它可以讓使用者透過(guò)特定的接口巡訪容器中的每一個(gè)元素而不用了解底層的實(shí)際操作。

適用性在希望利用語(yǔ)言本身的遍歷函數(shù)便利自定義結(jié)構(gòu)時(shí)，例如PHP中的foreach函數(shù)類(lèi)圖

PHP實(shí)例

<?phpclass sample implements Iterator { private $_items ; public function __construct(&$data) {$this->_items = $data; } public function current() {return current($this->_items); } public function next() {next($this->_items); } public function key() {return key($this->_items); } public function rewind() {reset($this->_items); } public function valid() { return ($this->current() !== FALSE); }} // client$data = array(1, 2, 3, 4, 5);$sa = new sample($data);foreach ($sa AS $key => $row) { echo $key, ’ ’, $row, ’<br />’;}?>在Yii框架中的實(shí)現(xiàn)：

在Yii框架中的我們可以看到其迭代器的實(shí)現(xiàn)，在collections目錄下的CMapIterator.php文件中，其實(shí)現(xiàn)如下：

class CMapIterator implements Iterator {/*** @var array the data to be iterated through*/ private $_d;/*** @var array list of keys in the map*/ private $_keys;/*** @var mixed current key*/ private $_key; /*** Constructor.* @param array the data to be iterated through*/ public function __construct(&$data) {$this->_d=&$data;$this->_keys=array_keys($data); } /*** Rewinds internal array pointer.* This method is required by the interface Iterator.*/ public function rewind() { $this->_key=reset($this->_keys); } /*** Returns the key of the current array element.* This method is required by the interface Iterator.* @return mixed the key of the current array element*/ public function key() {return $this->_key; } /*** Returns the current array element.* This method is required by the interface Iterator.* @return mixed the current array element*/ public function current() {return $this->_d[$this->_key]; } /*** Moves the internal pointer to the next array element.* This method is required by the interface Iterator.*/ public function next() {$this->_key=next($this->_keys); } /*** Returns whether there is an element at current position.* This method is required by the interface Iterator.* @return boolean*/ public function valid() {return $this->_key!==false; }} $data = array(’s1’ => 11, ’s2’ => 22, ’s3’ => 33);$it = new CMapIterator($data);foreach ($it as $row) { echo $row, ’<br />’;}

這與之前的簡(jiǎn)單實(shí)現(xiàn)相比，其位置的變化是通過(guò)控制key來(lái)實(shí)現(xiàn)的，這種實(shí)現(xiàn)的作用是為了避免false作為數(shù)組值時(shí)無(wú)法迭代。