PHP SPL标准库之接口(Interface)详解

PHP SPL标准库总共有6个接口，如下：

1.Countable2.OuterIterator 3.RecursiveIterator 4.SeekableIterator5.SplObserver 6.SplSubject

其中OuterIterator、RecursiveIterator、SeekableIterator都是继承Iterator类的，下面会对每种接口作用和使用进行详细说明。

Coutable接口：

实现Countable接口的对象可用于count()函数计数。复制代码 代码如下:class Mycount implements Countable{    public function count()    {        static $count = 0;        $count++;        return $count;    }} $count = new Mycount();$count->count();$count->count(); echo count($count); //3echo count($count); //4

说明：

调用count()函数时，Mycount::count()方法被调用count()函数的第二个参数将不会产生影响

OuterIterator接口：

自定义或修改迭代过程。复制代码 代码如下://IteratorIterator是OuterIterator的一个实现类class MyOuterIterator extends  IteratorIterator {     public function current()    {        return parent::current() . "TEST";    }} foreach(new MyOuterIterator(new ArrayIterator(["b","a","c"])) as $key => $value) {    echo "$key->$value".PHP_EOL;}/*结果：0->bTEST1->aTEST2->cTEST*/

在实际运用中，OuterIterator极其有用：

复制代码 代码如下:$db = new PDO("mysql:host=localhost;dbname=test", "root", "mckee");$db->query("set names utf8");$pdoStatement = $db->query("SELECT * FROM test1", PDO::FETCH_ASSOC);$iterator = new IteratorIterator($pdoStatement);$tenRecordArray = iterator_to_array($iterator);print_r($tenRecordArray);

RecursiveIterator接口：用于循环迭代多层结构的数据，RecursiveIterator另外提供了两个方法：

RecursiveIterator::getChildren 获取当前元素下子迭代器RecursiveIterator::hasChildren 判断当前元素下是否有迭代器

复制代码 代码如下:class MyRecursiveIterator implements RecursiveIterator{    private $_data;    private $_position = 0;     public function __construct(array $data) {        $this->_data = $data;    }     public function valid() {        return isset($this->_data[$this->_position]);    }     public function hasChildren() {        return is_array($this->_data[$this->_position]);    }     public function next() {        $this->_position++;    }     public function current() {        return $this->_data[$this->_position];    }     public function getChildren() {        print_r($this->_data[$this->_position]);    }     public function rewind() {        $this->_position = 0;    }     public function key() {        return $this->_position;    }} $arr = array(0, 1=> array(10, 20), 2, 3 => array(1, 2));$mri = new MyRecursiveIterator($arr); foreach ($mri as $c => $v) {    if ($mri->hasChildren()) {        echo "$c has children: " .PHP_EOL;        $mri->getChildren();    } else {        echo "$v" .PHP_EOL;    } }/*结果：01 has children:Array(    [0] => 10    [1] => 20)23 has children:Array(    [0] => 1    [1] => 2)*/

SeekableIterator接口：

通过seek()方法实现可搜索的迭代器，用于搜索某个位置下的元素。复制代码 代码如下:class  MySeekableIterator  implements  SeekableIterator  {     private  $position = 0;     private  $array  = array(        "first element" ,        "second element" ,        "third element" ,        "fourth element"    );     public function  seek ( $position ) {        if (!isset( $this -> array [ $position ])) {            throw new  OutOfBoundsException ( "invalid seek position ( $position )" );        }        $this -> position  =  $position ;    }     public function  rewind () {        $this -> position  =  0 ;    }     public function  current () {        return  $this -> array [ $this -> position ];    }     public function  key () {        return  $this -> position ;    }     public function  next () {        ++ $this -> position ;    }     public function  valid () {        return isset( $this -> array [ $this -> position ]);    }} try {     $it  = new  MySeekableIterator ;    echo  $it -> current (),  "" ;     $it -> seek ( 2 );    echo  $it -> current (),  "" ;     $it -> seek ( 1 );    echo  $it -> current (),  "" ;     $it -> seek ( 10 ); } catch ( OutOfBoundsException $e ) {    echo  $e -> getMessage ();}/*结果：first elementthird elementsecond elementinvalid seek position ( 10 )*/

SplObserver和SplSubject接口:SplObserver和SplSubject接口用来实现观察者设计模式，观察者设计模式是指当一个类的状态发生变化时，依赖它的对象都会收到通知并更新。使用场景非常广泛，比如说当一个事件发生后，需要更新多个逻辑操作，传统方式是在事件添加后编写逻辑，这种代码耦合并难以维护，观察者模式可实现低耦合的通知和更新机制。看看SplObserver和SplSubject的接口结构：复制代码 代码如下://SplSubject结构 被观察的对象interface SplSubject{    public function attach(SplObserver $observer); //添加观察者    public function detach(SplObserver $observer); //剔除观察者    public function notify(); //通知观察者} //SplObserver结构 代表观察者interface SplObserver{    public function update(SplSubject $subject); //更新操作}

看下面一个实现观察者的例子：

复制代码 代码如下:class Subject implements SplSubject{    private $observers = array();     public function attach(SplObserver  $observer)    {        $this->observers[] = $observer;    }     public function detach(SplObserver  $observer)    {        if($index = array_search($observer, $this->observers, true)) {            unset($this->observers[$index]);        }    }     public function notify()    {        foreach($this->observers as $observer) {            $observer->update($this);        }    }  } class Observer1 implements  SplObserver{    public function update(SplSubject  $subject)    {        echo "逻辑1代码".PHP_EOL;    }} class Observer2 implements  SplObserver{    public function update(SplSubject  $subject)    {        echo "逻辑2代码".PHP_EOL;    }}  $subject = new Subject();$subject->attach(new Observer1());$subject->attach(new Observer2()); $subject->notify();/*结果：逻辑1代码逻辑2代码*/