1.选择一个最合适的设计模式
没有任何事物是完美的，也没有人说过设计模式一个严格的放之四海而皆准的解决方法。因此你可以改变这些模式，使它们更适合手头的工作。对于某些设计模式而言，他们就是所属程序固有的天性；而对于其他的一些设计模式，你可以改变其自身的模式。模式之间互相配合、协同工作已经很常见。它们构成了整个应用（至少一部分）的基础。
2.单例模式
实例代码：
// The Database class represents our global DB connection
class Database{
// A static variable to hold our single instance
private static $_instance = null;
// Make the constructor private to ensure singleton
private function __construct()
{
echo 'constructor';
}
// A method to get our singleton instance
public static function getInstance()
{
if (!(self::$_instance instanceof Database)) {
self::$_instance = new Database();
}
return self::$_instance;
}
}
$database = Database::getInstance();
var_dump($database);
问题：使用单例模式不能创建两个实例，可用Traits解决创建两个不同类型的实例的问题,但仍然不能解决创建两个相同实例的问题（可用注册表模式解决）。
创建两个不同类的实例 代码：
trait Singleton {
private static $_instance = null;
public static function getInstance() {
$class = __CLASS__;
if(!(self::$_instance instanceof $class)) {
self::$_instance = new $class;
}
return self::$_instance;
}
}
class DB {
}
class DBWriteConnection extends DB {
use Singleton;
private function __construct() {
echo 'DBWriteConnection<br/>';
}
}
class DBReadConnection extends DB {
use Singleton;
private function __construct() {
echo 'DBReadConnection<br/>';
}
}
$dbWriteConnection = DBWriteConnection::getInstance();
var_dump($dbWriteConnection);
3.注册表模式
注册表模式仅仅是一个单独的全局类，在你需要的时候允许代码检索一个对象的相同实例，也可以在你需要的时创建另一个实例（一经要求将再次访问那些全局实例）。
Registry类：
class Registry {
/**
* @var array The store for all of our objects
*/
static private $_store = array();
/**
* Add an object to the registry
*
* If you do not specify a name the classname is used
*
* @param mixed $object The object to store
* @param string $name Name used to retrieve the object
* @return void
* @throws Exception
*/
static public function add($object, $name = null)
{
// Use the classname if no name given, simulates singleton
$name = (!is_null($name)) ?$name:get_class($object);
if (isset(self::$_store[$name])) {
throw new Exception("Object already exists in registry");
}
self::$_store[$name]= $object;
}
/**
* Get an object from the registry
*
* @param string $name Object name, {@see self::set()}
* @return mixed
* @throws Exception
*/
static public function get($name)
{
if (!self::contains($name)) {
throw new Exception("Object does not exist in registry");
}
return self::$_store[$name];
}
/**
* Check if an object is in the registry
*
* @param string $name Object name, {@see self::set()}
* @return bool
*/
static public function contains($name)
{
if (!isset(self::$_store[$name])) {
return false;
}
return true;
}
/**
* Remove an object from the registry
*
* @param string $name Object name, {@see self::set()}
* @returns void
*/
static public function remove($name)
{
if (self::contains($name)) {
unset(self::$_store[$name]);
}
}
}
在类外部，使用Registry类：
require 'Registry.php';
class DBReadConnection {}
class DBWriteConnection {}
$read = new DBReadConnection;
Registry::add($read);
$write = new DBWriteConnection;
Registry::add($write);
// To get the instances, anywhere in our code:
$read = Registry::get('DBReadConnection');
$write = Registry::get('DBWriteConnection');
var_dump($read);
var_dump($write);
在类内部使用Registry表类，使用者不与Registry交互。
示例代码：
require 'Registry.php';
abstract class DBConnection {
static public function getInstance($name = null)
{
// Get the late-static-binding version of __CLASS__
$class = get_called_class();
// Allow passing in a name to get multiple instances
// If you do not pass a name, it functions as a singleton
$name = (!is_null($name)) ? $name:$class;
if (!Registry::contains($name)) {
$instance = new $class();
Registry::add($instance, $name);
}
return Registry::get($name);
}
}
class DBWriteConnection extends DBConnection {
public function __construct()
{
echo 'DBWriteConnection<br/>';
}
}
class DBReadConnection extends DBConnection {
public function __construct()
{
echo 'DBReadConnection<br/>';
}
}
$dbWriteConnection = DBWriteConnection::getInstance('abc');
var_dump($dbWriteConnection);
$dbReadConnection = DBReadConnection::getInstance();
var_dump($dbReadConnection);
4.工厂模式
工厂（factory）模式制造对象，就像工业界与它同名的钢筋混泥土行业一样。通常，我们将工厂模式用于初始化相同抽象类或者接口的具体实现。
在通常方式下，虽然人们极少采用工厂模式，但是它仍是最适合初始化基于驱动安装的许多变种的一种。例如不同的配置、会话或缓存存储引擎。工厂模式的最大价值在于它可以将多个对象设置封装成单一、简单的方法调用。
示例代码：
/**
* Log Factory
*
* Setup and return a file, mysql, or sqlite logger
*/
class Log_Factory {
/**
* Get a log object
*
* @param string $type The type of logging backend, file, mysql or sqlite
* @param array $options Log class options
*/
public function getLog($type = 'file', array $options)
{
// Normalize the type to lowercase
$type = strtolower($type);
// Figure out the class name and include it
$class = "Log_" .ucfirst($type);
require_once str_replace('_', DIRECTORY_SEPARATOR, $class) . '.php';
// Instantiate the class and set the appropriate options
$log = new $class($options);
switch ($type) {
case 'file':
$log->setPath($options['location']);
break;
case 'mysql':
$log->setUser($options['username']);
$log->setPassword($options['password']);
$log->setDBName($options['location']);
break;
case 'sqlite':
$log->setDBPath($otions['location']);
break;
}
return $log;
}
}
5.迭代模式
迭代模式允许我们将foreach的性能添加到任何对象的内部存储数据，而不仅仅添加到公共属性。它覆盖了默认的foreach行为，并允许我们为循环注入业务逻辑。
（1）使用Iterator迭代器接口
class BasicIterator implements Iterator {
private $key = 0;
private $data = array(
"hello",
"world",
);
public function __construct() {
$this->key = 0;
}
public function rewind() {
$this->key = 0;
}
public function current() {
return $this->data[$this->key];
}
public function key() {
return $this->key;
}
public function next() {
$this->key++;
return true;
}
public function valid() {
return isset($this->data[$this->key]);
}
}
$iterator = new BasicIterator();
$iterator->rewind();
do {
$key = $iterator->key();
$value = $iterator->current();
echo $key .': ' .$value . PHP_EOL;
} while ($iterator->next() && $iterator->valid());
$iterator = new BasicIterator();
foreach ($iterator as $key => $value) {
echo $key .': ' .$value . PHP_EOL;
}
（2）使用RecursiveIteratorIterator迭代器遍历数组
$array = array(
"Hello", // Level 1
array(
"World" // Level 2
),
array(
"How", // Level 2
array(
"are", // Level 3
"you" // Level 3
)
),
"doing?" // Level 1
);
$recursiveIterator = new RecursiveArrayIterator($array);
$recursiveIteratorIterator = new RecursiveIteratorIterator($recursiveIterator);
foreach ($recursiveIteratorIterator as $key => $value) {
echo "Depth: " . $recursiveIteratorIterator->getDepth() . PHP_EOL;
echo "Key: " . $key . PHP_EOL;
echo "Value: " .$value . PHP_EOL;
}
（3）用FilterIterator迭代器实现过滤
代码：
<?php
class EvenFilterIterator extends FilterIterator {
/**
* Accept only even-keyed values
*
* @return bool
*/
public function accept()
{
// Get the actual iterator
$iterator = $this->getInnerIterator();
// Get the current key
$key = $iterator->key();
// Check for even keys
if ($key % 2 == 0) {
return true;
}
return false;
}
}
$array = array(
0 => "Hello",
1 => "Everybody Is",
2 => "I'm",
3 => "Amazing",
4 => "The",
5 => "Who",
6 => "Doctor",
7 => "Lives"
);
// Create an iterator from our array
$iterator = new ArrayIterator($array);
// Create our FilterIterator
$filterIterator = new EvenFilterIterator($iterator);
// Iterate
foreach ($filterIterator as $key => $value) {
echo $key .': '. $value . PHP_EOL;
}
?>
（4）RegexIterator迭代器
<?php
// Create a RecursiveDirectoryIterator
$directoryIterator = new RecursiveDirectoryIterator("./");
// Create a RecursiveIteratorIterator to recursively iterate
$recursiveIterator = new RecursiveIteratorIterator($directoryIterator);
// Createa filter for *Iterator*.php files
$regexFilter = new RegexIterator($recursiveIterator, '/(.*?)Iterator(.*?)\.php$/');
// Iterate
foreach ($regexFilter as $key => $file) {
/* @var SplFileInfo $file */
echo $file->getFilename() . PHP_EOL;
}
功能：找到所有的php文件
（4）LimitItertor迭代器，像SQL中的LIMIT
// Define the array
$array = array(
'Hello',
'World',
'How',
'are',
'you',
'doing?'
);
// Create the iterator
$iterator = new ArrayIterator($array);
// Create the limiting iterator, to get the first 2 elements
$limitIterator = new LimitIterator($iterator, 0, 2);
// Iterate
foreach ($limitIterator as $key => $value) {
echo $key .': '. $value . PHP_EOL;
}
6.观察者模式（observer）
观察者模式的核心在于云霄你的应用程序注册一个回调，当某个特定的事件发生时便会促发它
代码示例：
<?php
/**
* The Event Class
*
* With this class you can register callbacks that will
* be called (FIFO) for a given event.
*/
class Event {
/**
* @var array A multi-dimentional array of events => callbacks
*/
static protected $callbacks = array();
/**
* Register a callback
*
* @param string $eventName Name of the triggering event
* @param mixed $callback An instance of Event_Callback or a Closure
*/
static public function registerCallback($eventName, $callback)
{
if (!($callback instanceof Event_Callback) && !($callback instanceof Closure)) {
throw new Exception("Invalid callback!");
}
$eventName = strtolower($eventName);
self::$callbacks[$eventName][] = $callback;
}
/**
* Trigger an event
*
* @param string $eventName Name of the event to be triggered
* @param mixed $data The data to be sent to the callback
*/
static public function trigger($eventName, $data)
{
$eventName = strtolower($eventName);
if (isset(self::$callbacks[$eventName])) {
foreach (self::$callbacks[$eventName] as $callback) {
self::callback($callback, $data);
}
}
}
/**
* Perform the callback
*
* @param mixed $callback An instance of Event_Callback or a Closure
* @param mixed $data The data sent to the callback
*/
static protected function callback($callback, $data)
{
if ($callback instanceof Closure) {
$callback($data);
} else {
$callback->run($data);
}
}
}
/**
* The Event Callback interface
*
* If you do not wish to use a closure
* you can define a class that extends
* this instead. The run method will be
* called when the event is triggered.
*/
interface Event_Callback {
public function run($data);
}
/**
* Logger callback
*/
class LogCallback implements Event_Callback {
public function run($data)
{
echo "Log Data" . PHP_EOL;
var_dump($data);
}
}
// Register the log callback
Event::registerCallback('save', new LogCallback());
// Register the clear cache callback as a closure
Event::registerCallback('save', function ($data) {
echo "Clear Cache" . PHP_EOL;
var_dump($data);
});
class MyDataRecord {
public function save()
{
// Save data
// Trigger the save event
Event::trigger('save', array("Hello", "World"));
}
}
// Instantiate a new data record
$data = new MyDataRecord();
$data->save(); // 'save' Event is triggered here
7.依赖注入模式
依赖注入模式允许类的使用这为这个类注入依赖的行为。
代码示例：
/**
* Log Class
*/
class Log {
/**
* @var Log_Engine_Interface
*/
protected $engine = false;
/**
* Add an event to the log
*
* @param string $message
*/
public function add($message)
{
if (!$this->engine) {
throw new Exception('Unable to write log. No Engine set.');
}
$data['datetime'] = time();
$data['message'] = $message;
$session = Registry::get('session');
$data['user'] = $session->getUserId();
$this->engine->add($data);
}
/**
* Set the log data storage engine
*
* @param Log_Engine_Interface $Engine
*/
public function setEngine(Log_Engine_Interface $engine)
{
$this->engine = $engine;
}
/**
* Retrieve the data storage engine
*
* @return Log_Engine_Interface
*/
public function getEngine()
{
return $this->engine;
}
}
interface Log_Engine_Interface {
/**
* Add an event to the log
*
* @param string $message
*/
public function add(array $data);
}
class Log_Engine_File implements Log_Engine_Interface {
/**
* Add an event to the log
*
* @param string $message
*/
public function add(array $data)
{
$line = '[' .data('r', $data['datetime']). '] ' .$data['message']. ' User: ' .$data['user'] . PHP_EOL;
$config = Registry::get('site-config');
if (!file_put_contents($config['location'], $line, FILE_APPEND)) {
throw new Exception("An error occurred writing to file.");
}
}
}
$engine = new Log_Engine_File();
$log = new Log();
$log->setEngine($engine);
// Add it to the registry
Registry::add($log);
依赖注入不想工厂模式，日之类无需了解每一个不同的存储引擎的相关知识。这就意味着任何使用日志类的开发者可以添加他们自己的存储引擎，主要他们复合接口就行。
8.模型-视图-控制器
模型-视图-控制器又称为MVC模式，是描述应用程序3个不同层次之间关系的一种方式。
模型-数据层 所有的输出数据都来自模型。它可能是一个数据库、web服务或者文件。
视图-表现层 负责将数据从模型中取出并输出给用户。
控制器-应用程序流层 根据用户的请求调用相应的模型检索出请求的数据，然后调用视图将操作的结果显示给用户。
一个典型的MVC架构图：
9.对模式的理解
模式是很多常见问题的最佳解决方法。