Php/docs/language.oop5.iterations
遍历对象
PHP 5 提供了一种定义对象的方法使其可以通过单元列表来遍历,例如用 foreach 语句。默认情况下,所有可见属性都将被用于遍历。
Example #1 简单的对象遍历
<?phpclass MyClass{ public $var1 = 'value 1'; public $var2 = 'value 2'; public $var3 = 'value 3'; protected $protected = 'protected var'; private $private = 'private var'; function iterateVisible() { echo "MyClass::iterateVisible:\n"; foreach($this as $key => $value) { print "$key => $value\n"; } }}$class = new MyClass();foreach($class as $key => $value) { print "$key => $value\n";}echo "\n";$class->iterateVisible();?>
以上例程会输出:
var1 => value 1 var2 => value 2 var3 => value 3 MyClass::iterateVisible: var1 => value 1 var2 => value 2 var3 => value 3 protected => protected var private => private var
更进一步,可以实现 Iterator 接口。可以让对象自行决定如何遍历以及每次遍历时那些值可用。
Example #2 实现 Iterator 接口的对象遍历
<?phpclass MyIterator implements Iterator{ private $var = array(); public function __construct($array) { if (is_array($array)) { $this->var = $array; } } public function rewind() { echo "rewinding\n"; reset($this->var); } public function current() { $var = current($this->var); echo "current: $var\n"; return $var; } public function key() { $var = key($this->var); echo "key: $var\n"; return $var; } public function next() { $var = next($this->var); echo "next: $var\n"; return $var; } public function valid() { $var = $this->current() !== false; echo "valid: {$var}\n"; return $var; }}$values = array(1,2,3);$it = new MyIterator($values);foreach ($it as $a => $b) { print "$a: $b\n";}?>
以上例程会输出:
rewinding current: 1 valid: 1 current: 1 key: 0 0: 1 next: 2 current: 2 valid: 1 current: 2 key: 1 1: 2 next: 3 current: 3 valid: 1 current: 3 key: 2 2: 3 next: current: valid:
可以用 IteratorAggregate 接口以替代实现所有的 Iterator 方法。IteratorAggregate 只需要实现一个方法 IteratorAggregate::getIterator(),其应返回一个实现了 Iterator 的类的实例。
Example #3 通过实现 IteratorAggregate 来遍历对象
<?phpclass MyCollection implements IteratorAggregate{ private $items = array(); private $count = 0; // Required definition of interface IteratorAggregate public function getIterator() { return new MyIterator($this->items); } public function add($value) { $this->items[$this->count++] = $value; }}$coll = new MyCollection();$coll->add('value 1');$coll->add('value 2');$coll->add('value 3');foreach ($coll as $key => $val) { echo "key/value: [$key -> $val]\n\n";}?>
以上例程会输出:
rewinding current: value 1 valid: 1 current: value 1 key: 0 key/value: [0 -> value 1] next: value 2 current: value 2 valid: 1 current: value 2 key: 1 key/value: [1 -> value 2] next: value 3 current: value 3 valid: 1 current: value 3 key: 2 key/value: [2 -> value 3] next: current: valid:
Note:
更多遍历的示例见 SPL 扩展。
Note:
PHP 5.5 及以后版本的用户也可参考生成器,其提供了另一方法来定义 Iterators。