PHP SPL标准库总共有6个接口，如下：
1.Countable
2.OuterIterator
3.RecursiveIterator
4.SeekableIterator
5.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。
class Mycount implements Countable
{
public function count()
{
static $count = 0;
$count++;
return $count;
}
}
$count = new Mycount();
$count->count();
$count->count();
echo count($count); //3
echo 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。
//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->bTEST
1->aTEST
2->cTEST
*/
在实际运用中，OuterIterator极其有用：
$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
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：
0
1 has children:
Array
(
[0] => 10
[1] => 20
)
2
3 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。
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 (), "\n" ;
$it -> seek ( 2 );
echo $it -> current (), "\n" ;
$it -> seek ( 1 );
echo $it -> current (), "\n" ;
$it -> seek ( 10 );
} catch ( OutOfBoundsException $e ) {
echo $e -> getMessage ();
}
/*
结果：
first element
third element
second element
invalid 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：
//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：
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
*/