????????首先了解觀察者模式的概念：一個(gè)對(duì)象通過(guò)添加一個(gè)方法（該方法允許另一個(gè)對(duì)象，即觀察者 注冊(cè)自己）使本身變得可觀察。當(dāng)可觀察的對(duì)象更改時(shí)，它會(huì)將消息發(fā)送到已注冊(cè)的觀察者。這些觀察者使用該信息執(zhí)行的操作與可觀察的對(duì)象無(wú)關(guān)。結(jié)果是對(duì)象可以相互對(duì)話(huà)，而不必了解原因。觀察者模式是一種事件系統(tǒng)，意味著這一模式允許某個(gè)類(lèi)觀察另一個(gè)類(lèi)的狀態(tài)，當(dāng)被觀察的類(lèi)狀態(tài)發(fā)生改變的時(shí)候，觀察類(lèi)可以收到通知并且做出相應(yīng)的動(dòng)作;觀察者模式為您提供了避免組件之間緊密耦。
觀察者模式解決的問(wèn)題
????????在我們的開(kāi)發(fā)過(guò)程中，應(yīng)該都或多或少的碰到過(guò)改動(dòng)其中一部分代碼會(huì)引起其他一連串改變的問(wèn)題，顯然想要完全避免這種情況不太可能，但我們也應(yīng)答盡量減少對(duì)其他組件的依賴(lài)，而觀察者模式就是為了解決這個(gè)問(wèn)題。
舉個(gè)例子來(lái)說(shuō)，我們有一個(gè)帖子對(duì)象，代碼如下：
class Post
{
????????protected $_userid = null;
????????protected $_ip = null;
????????protected $_content = null;
????????function __construct()
????????{
????????????????// ...
????????}
????????// 發(fā)帖方法
????????public function addPost()
????????{
????????????????// ... 發(fā)帖邏輯
????????}
}
????????在上面是一個(gè)普通的帖子對(duì)象，隨著發(fā)帖量和訪(fǎng)問(wèn)量越來(lái)越大，運(yùn)營(yíng)們開(kāi)始不干了，公司也經(jīng)常會(huì)接到投訴電話(huà)，說(shuō)我們的網(wǎng)站有許多敏感內(nèi)容和垃圾廣告，因此我們需要做內(nèi)容審核：首先是對(duì)用戶(hù)的審核，一些黑名單用戶(hù)應(yīng)該被禁止發(fā)帖；二是對(duì)IP的審核；三是對(duì)內(nèi)容敏感詞的審核。因此我們的代碼就成了如下的樣子：
class Post
{
????????protected $_userid = null;
????????protected $_ip = null;
????????protected $_content = null;
????????function __construct(){}
????????public function addPost()
????????{
????????????????if (!Postscan::checkUserid($tihs->_userid)) {
????????????????????????return false;
????????????????}
????????????????if (!Postscan::ipUserid($tihs->_ip)) {
????????????????????????return false;
????????????????}
????????????????if (!Postscan::checkContent($tihs->_content)) {
????????????????????????return false;
????????????????}
????????????????// ...
????????}
}
????????隨著需要審核的字段越來(lái)越多，addPost方法變得越來(lái)越長(zhǎng)，發(fā)布對(duì)象被也只能緊緊的被嵌入到該系統(tǒng)中。
觀察者模式的實(shí)現(xiàn)
觀察者模式的核心是把觀察者從主體中分離開(kāi)來(lái)，當(dāng)主體知道事件發(fā)生時(shí)，觀察需要被通知到，同時(shí)我們也不想把主體和觀察者之間的關(guān)系寫(xiě)死，于是我們來(lái)修改下我們上面的代碼：
//主體必須實(shí)現(xiàn)的接口
interface Observable
{
????????public function attach(Observer $observer);
????????public function detach(Observer $observer);
????????public function notify();
}
//觀察者必須實(shí)現(xiàn)的接口
interface Observer
{
????????public function do(Observable $subject);
}
class Post implements Observable
{
????????protected $_userid = null;
????????protected $_ip = null;
????????protected $_content = null;
????????protected $_observerlist = array();
????????function __construct(){}
????????public function attach(Observer $observer)
????????{
????????????????$this->_observerlist[] = $observer;
????????}
????????public function detach(Observer $observer){
????????????????foreach ($this->_observerlist as $key => $value) {
????????????????????????if ($observer === $value) {
????????????????????????????????unset($this->_observerlist[$key]);
????????????????????????}
????????????????}
????????}
????????public function notify()
????????{
????????????????foreach ($this->_observerlist as $value) {
????????????????????????if (!$value->do($this)) {
????????????????????????????????return false;
????????????????????????}
????????????????}
????????return true;
????????}
????????public function addPost()
????????{
????????????????if (!$this->notify()) {
????????????????????????return false;
? ? ? ? ????????}
????????????????// ...
????????}
}
通過(guò)上面的代碼，我們可以再很容易的加入審核規(guī)則。
SPL代碼
????????觀察者模式是一個(gè)很常見(jiàn)和常用的設(shè)計(jì)模式，以至于SPL擴(kuò)展已經(jīng)為我們封裝好了對(duì)應(yīng)的類(lèi)和方法，下面的代碼是根據(jù)SPL提供的3個(gè)元素：SplObserver,SplSubject,SplObjectStorage來(lái)實(shí)現(xiàn)的代碼
class Post implements SplSubject
{
????????protected $_userid = null;
????????protected $_ip = null;
????????protected $_content = null;
????????protected $_storage = new SplObjectStorage();
????????function __construct(){}
????????public function attach(SplObject $observer)
????????{
????????????????$this->_storage->attach($observer);
????????}
????????public function detach(SplObject $observer)
????????{
????????????????$this->_storage->detach($observer);
????????}
????????public function notify()
????????{
????????????????foreach ($this->_storage as $value){
????????????????????????if (!$value->update($this)) {
????????????????????????????????return false;
????????????????????????}
????????????????}
????????????????return true;
????????}
????????public function addPost()
????????{
????????????????if (!$this->notify()) {
????????????????????????return false;
????????????????}
????????????????// ...
????????}
}
????????圖片與文章無(wú)關(guān)，在閱讀技術(shù)文檔的時(shí)候欣賞一下美女也是一個(gè)不錯(cuò)的選擇，希望可以對(duì)你有幫助，如果有錯(cuò)誤的地方歡迎指正。
