layout: post
title: "PHP设计模式(八)-迭代器模式"
date: 2016-06-07 12:59:44 +0800
comments: true
categories: [php]
1、模式定义
迭代器模式（Iterator），又叫做游标（Cursor）模式。提供一种方法访问一个容器（Container）对象中各个元素，而又不需暴露该对象的内部细节。
当你需要访问一个聚合对象，而且不管这些对象是什么都需要遍历的时候，就应该考虑使用迭代器模式。另外，当需要对聚集有多种方式遍历时，可以考虑去使用迭代器模式。迭代器模式为遍历不同的聚集结构提供如开始、下一个、是否结束、当前哪一项等统一的接口。
PHP标准库（SPL）中提供了迭代器接口 Iterator，要实现迭代器模式，实现该接口即可。
2、UML类图
image
3、实例代码
<?php
namespace DesignPatterns\Behavioral\Iterator;
class Book
{
private $author;
private $title;
public function __construct($title, $author)
{
$this->author = $author;
$this->title = $title;
}
public function getAuthor()
{
return $this->author;
}
public function getTitle()
{
return $this->title;
}
public function getAuthorAndTitle()
{
return $this->getTitle() . ' by ' . $this->getAuthor();
}
}
<?php
namespace DesignPatterns\Behavioral\Iterator;
class BookList implements \Countable
{
private $books;
public function getBook($bookNumberToGet)
{
if (isset($this->books[$bookNumberToGet])) {
return $this->books[$bookNumberToGet];
}
return null;
}
public function addBook(Book $book)
{
$this->books[] = $book;
}
public function removeBook(Book $bookToRemove)
{
foreach ($this->books as $key => $book) {
/** @var Book $book */
if ($book->getAuthorAndTitle() === $bookToRemove->getAuthorAndTitle()) {
unset($this->books[$key]);
}
}
}
public function count()
{
return count($this->books);
}
}
<?php
namespace DesignPatterns\Behavioral\Iterator;
class BookListIterator implements \Iterator
{
/**
* @var BookList
*/
private $bookList;
/**
* @var int
*/
protected $currentBook = 0;
public function __construct(BookList $bookList)
{
$this->bookList = $bookList;
}
/**
* Return the current book
* @link http://php.net/manual/en/iterator.current.php
* @return Book Can return any type.
*/
public function current()
{
return $this->bookList->getBook($this->currentBook);
}
/**
* (PHP 5 >= 5.0.0)
*
* Move forward to next element
* @link http://php.net/manual/en/iterator.next.php
* @return void Any returned value is ignored.
*/
public function next()
{
$this->currentBook++;
}
/**
* (PHP 5 >= 5.0.0)
*
* Return the key of the current element
* @link http://php.net/manual/en/iterator.key.php
* @return mixed scalar on success, or null on failure.
*/
public function key()
{
return $this->currentBook;
}
/**
* (PHP 5 >= 5.0.0)
*
* Checks if current position is valid
* @link http://php.net/manual/en/iterator.valid.php
* @return boolean The return value will be casted to boolean and then evaluated.
* Returns true on success or false on failure.
*/
public function valid()
{
return null !== $this->bookList->getBook($this->currentBook);
}
/**
* (PHP 5 >= 5.0.0)
*
* Rewind the Iterator to the first element
* @link http://php.net/manual/en/iterator.rewind.php
* @return void Any returned value is ignored.
*/
public function rewind()
{
$this->currentBook = 0;
}
}
<?php
namespace DesignPatterns\Behavioral\Iterator;
class BookListReverseIterator implements \Iterator
{
/**
* @var BookList
*/
private $bookList;
/**
* @var int
*/
protected $currentBook = 0;
public function __construct(BookList $bookList)
{
$this->bookList = $bookList;
$this->currentBook = $this->bookList->count() - 1;
}
/**
* Return the current book
* @link http://php.net/manual/en/iterator.current.php
* @return Book Can return any type.
*/
public function current()
{
return $this->bookList->getBook($this->currentBook);
}
/**
* (PHP 5 >= 5.0.0)
*
* Move forward to next element
* @link http://php.net/manual/en/iterator.next.php
* @return void Any returned value is ignored.
*/
public function next()
{
$this->currentBook--;
}
/**
* (PHP 5 >= 5.0.0)
*
* Return the key of the current element
* @link http://php.net/manual/en/iterator.key.php
* @return mixed scalar on success, or null on failure.
*/
public function key()
{
return $this->currentBook;
}
/**
* (PHP 5 >= 5.0.0)
*
* Checks if current position is valid
* @link http://php.net/manual/en/iterator.valid.php
* @return boolean The return value will be casted to boolean and then evaluated.
* Returns true on success or false on failure.
*/
public function valid()
{
return null !== $this->bookList->getBook($this->currentBook);
}
/**
* (PHP 5 >= 5.0.0)
*
* Rewind the Iterator to the first element
* @link http://php.net/manual/en/iterator.rewind.php
* @return void Any returned value is ignored.
*/
public function rewind()
{
$this->currentBook = $this->bookList->count() - 1;
}
}
4、测试代码
<?php
namespace DesignPatterns\Behavioral\Iterator\Tests;
use DesignPatterns\Behavioral\Iterator\Book;
use DesignPatterns\Behavioral\Iterator\BookList;
use DesignPatterns\Behavioral\Iterator\BookListIterator;
use DesignPatterns\Behavioral\Iterator\BookListReverseIterator;
class IteratorTest extends \PHPUnit_Framework_TestCase
{
/**
* @var BookList
*/
protected $bookList;
protected function setUp()
{
$this->bookList = new BookList();
$this->bookList->addBook(new Book('Learning PHP Design Patterns', 'William Sanders'));
$this->bookList->addBook(new Book('Professional Php Design Patterns', 'Aaron Saray'));
$this->bookList->addBook(new Book('Clean Code', 'Robert C. Martin'));
}
public function expectedAuthors()
{
return array(
array(
array(
'Learning PHP Design Patterns by William Sanders',
'Professional Php Design Patterns by Aaron Saray',
'Clean Code by Robert C. Martin'
)
),
);
}
/**
* @dataProvider expectedAuthors
*/
public function testUseAIteratorAndValidateAuthors($expected)
{
$iterator = new BookListIterator($this->bookList);
while ($iterator->valid()) {
$expectedBook = array_shift($expected);
$this->assertEquals($expectedBook, $iterator->current()->getAuthorAndTitle());
$iterator->next();
}
}
/**
* @dataProvider expectedAuthors
*/
public function testUseAReverseIteratorAndValidateAuthors($expected)
{
$iterator = new BookListReverseIterator($this->bookList);
while ($iterator->valid()) {
$expectedBook = array_pop($expected);
$this->assertEquals($expectedBook, $iterator->current()->getAuthorAndTitle());
$iterator->next();
}
}
/**
* Test BookList Remove
*/
public function testBookRemove()
{
$this->bookList->removeBook($this->bookList->getBook(0));
$this->assertEquals($this->bookList->count(), 2);
}
}
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