Zend Framework教程-Zend_Helpers-動作助手(Zend_Controller_Action_Helper)概述

通過助手模式，可以把一些經常使用的功能模塊做封裝，從而在可以在需要的地方靈活使用，主要是在action使用。
Zend Framework中有兩種助手，動作助手(Zend_Controller_Action_Helper)和試圖助手(Zend_View_Helper)。
動作助手可以向任何Zend_Controller_Action的衍生動作控制器中，即時的加入功能(runtime and/or on-demand functionality)，以使得增加公共的動作控制器功能時，盡量減少衍生動作控制器類的必要。 
動作助手在需要調用時加載，可以在請求的時候(bootstrap)或者動作控制器創建的時候(init())實例化。


涉及到的相關文件
在/library/Zend/Controller/Action/中


│  Exception.php
│  HelperBroker.php
│  Interface.php
│
├─Helper
│  │  Abstract.php
│  │  ActionStack.php
│  │  AjaxContext.php
│  │  AutoCompleteDojo.php
│  │  AutoCompleteScriptaculous.php
│  │  Cache.php
│  │  ContextSwitch.php
│  │  FlashMessenger.php
│  │  Json.php
│  │  Redirector.php
│  │  Url.php
│  │  ViewRenderer.php
│  │
│  └─AutoComplete
│          Abstract.php
│
└─HelperBroker
       PriorityStack.php


常見的動作助手有：
FlashMessenger 用來處理Flash Messenger會話；
Json 用來解碼和發送 JSON 響應；
Url  用于創建Urls；
Redirector 提供另一種實現方式，幫助程序重定向到內部或者外部頁面；
ViewRenderer 自動的完成在控制器內建立視圖對象并渲染視圖的過程；
AutoComplete 自動響應 AJAX 的自動完成；
ContextSwitch 和 AjaxContext 為你的動作提供替代響應格式；
Cache  實現cache的相關操作；
ActionStack 用于操作動作堆棧。


動手的幾種實例化使用方式
1.通過Zend_Controller_Action的 $_helper成員的getHelper()方法。直接調用getHelper()，傳入助手的名稱即可。


$redirector = $this->_helper->getHelper('Redirector'); 
//$redirector->getName();
$redirector->gotoSimple('index2');


2.直接通過訪問的_helper助手的屬性對應的助手對象。
$redirector = $this->_helper->Redirector;




Zend_Controller_Action_HelperBroker
中文名稱譯作"助手經紀人",顧名思義，是動作助手的中間人。
在動作的實例化使用的方式的第二種方式就是通過Zend_Controller_Action_HelperBroker的魔術方法__get()來實現的。
助手經紀人用于注冊助手對象和助手路徑以及獲取助手等等功能。 


Zend_Controller_Action_HelperBroker的實現以及常用方法列表

<?php /** * @see Zend_Controller_Action_HelperBroker_PriorityStack */require_once 'Zend/Controller/Action/HelperBroker/PriorityStack.php';/** * @see Zend_Loader */require_once 'Zend/Loader.php';/** * @category   Zend * @package    Zend_Controller * @subpackage Zend_Controller_Action * @copyright  Copyright (c) 2005-2011 Zend Technologies USA Inc. (http://www.zend.com) * @license    http://framework.zend.com/license/new-bsd     New BSD License */class Zend_Controller_Action_HelperBroker{    /**     * $_actionController - ActionController reference     *     * @var Zend_Controller_Action     */    protected $_actionController;    /**     * @var Zend_Loader_PluginLoader_Interface     */    protected static $_pluginLoader;    /**     * $_helpers - Helper array     *     * @var Zend_Controller_Action_HelperBroker_PriorityStack     */    protected static $_stack = null;    /**     * Set PluginLoader for use with broker     *     * @param  Zend_Loader_PluginLoader_Interface $loader     * @return void     */    public static function setPluginLoader($loader)    {        if ((null !== $loader) && (!$loader instanceof Zend_Loader_PluginLoader_Interface)) {            require_once 'Zend/Controller/Action/Exception.php';            throw new Zend_Controller_Action_Exception('Invalid plugin loader provided to HelperBroker');        }        self::$_pluginLoader = $loader;    }    /**     * Retrieve PluginLoader     *     * @return Zend_Loader_PluginLoader     */    public static function getPluginLoader()    {        if (null === self::$_pluginLoader) {            require_once 'Zend/Loader/PluginLoader.php';            self::$_pluginLoader = new Zend_Loader_PluginLoader(array(                'Zend_Controller_Action_Helper' => 'Zend/Controller/Action/Helper/',            ));        }        return self::$_pluginLoader;    }    /**     * addPrefix() - Add repository of helpers by prefix     *     * @param string $prefix     */    static public function addPrefix($prefix)    {        $prefix = rtrim($prefix, '_');        $path   = str_replace('_', DIRECTORY_SEPARATOR, $prefix);        self::getPluginLoader()->addPrefixPath($prefix, $path);    }    /**     * addPath() - Add path to repositories where Action_Helpers could be found.     *     * @param string $path     * @param string $prefix Optional; defaults to 'Zend_Controller_Action_Helper'     * @return void     */    static public function addPath($path, $prefix = 'Zend_Controller_Action_Helper')    {        self::getPluginLoader()->addPrefixPath($prefix, $path);    }    /**     * addHelper() - Add helper objects     *     * @param Zend_Controller_Action_Helper_Abstract $helper     * @return void     */    static public function addHelper(Zend_Controller_Action_Helper_Abstract $helper)    {        self::getStack()->push($helper);        return;    }    /**     * resetHelpers()     *     * @return void     */    static public function resetHelpers()    {        self::$_stack = null;        return;    }    /**     * Retrieve or initialize a helper statically     *     * Retrieves a helper object statically, loading on-demand if the helper     * does not already exist in the stack. Always returns a helper, unless     * the helper class cannot be found.     *     * @param  string $name     * @return Zend_Controller_Action_Helper_Abstract     */    public static function getStaticHelper($name)    {        $name  = self::_normalizeHelperName($name);        $stack = self::getStack();        if (!isset($stack->{$name})) {            self::_loadHelper($name);        }        return $stack->{$name};    }    /**     * getExistingHelper() - get helper by name     *     * Static method to retrieve helper object. Only retrieves helpers already     * initialized with the broker (either via addHelper() or on-demand loading     * via getHelper()).     *     * Throws an exception if the referenced helper does not exist in the     * stack; use {@link hasHelper()} to check if the helper is registered     * prior to retrieving it.     *     * @param  string $name     * @return Zend_Controller_Action_Helper_Abstract     * @throws Zend_Controller_Action_Exception     */    public static function getExistingHelper($name)    {        $name  = self::_normalizeHelperName($name);        $stack = self::getStack();        if (!isset($stack->{$name})) {            require_once 'Zend/Controller/Action/Exception.php';            throw new Zend_Controller_Action_Exception('Action helper "' . $name . '" has not been registered with the helper broker');        }        return $stack->{$name};    }    /**     * Return all registered helpers as helper => object pairs     *     * @return array     */    public static function getExistingHelpers()    {        return self::getStack()->getHelpersByName();    }    /**     * Is a particular helper loaded in the broker?     *     * @param  string $name     * @return boolean     */    public static function hasHelper($name)    {        $name = self::_normalizeHelperName($name);        return isset(self::getStack()->{$name});    }    /**     * Remove a particular helper from the broker     *     * @param  string $name     * @return boolean     */    public static function removeHelper($name)    {        $name = self::_normalizeHelperName($name);        $stack = self::getStack();        if (isset($stack->{$name})) {            unset($stack->{$name});        }        return false;    }    /**     * Lazy load the priority stack and return it     *     * @return Zend_Controller_Action_HelperBroker_PriorityStack     */    public static function getStack()    {        if (self::$_stack == null) {            self::$_stack = new Zend_Controller_Action_HelperBroker_PriorityStack();        }        return self::$_stack;    }    /**     * Constructor     *     * @param Zend_Controller_Action $actionController     * @return void     */    public function __construct(Zend_Controller_Action $actionController)    {        $this->_actionController = $actionController;        foreach (self::getStack() as $helper) {            $helper->setActionController($actionController);            $helper->init();        }    }    /**     * notifyPreDispatch() - called by action controller dispatch method     *     * @return void     */    public function notifyPreDispatch()    {        foreach (self::getStack() as $helper) {            $helper->preDispatch();        }    }    /**     * notifyPostDispatch() - called by action controller dispatch method     *     * @return void     */    public function notifyPostDispatch()    {        foreach (self::getStack() as $helper) {            $helper->postDispatch();        }    }    /**     * getHelper() - get helper by name     *     * @param  string $name     * @return Zend_Controller_Action_Helper_Abstract     */    public function getHelper($name)    {        $name  = self::_normalizeHelperName($name);        $stack = self::getStack();        if (!isset($stack->{$name})) {            self::_loadHelper($name);        }        $helper = $stack->{$name};        $initialize = false;        if (null === ($actionController = $helper->getActionController())) {            $initialize = true;        } elseif ($actionController !== $this->_actionController) {            $initialize = true;        }        if ($initialize) {            $helper->setActionController($this->_actionController)                   ->init();        }        return $helper;    }    /**     * Method overloading     *     * @param  string $method     * @param  array $args     * @return mixed     * @throws Zend_Controller_Action_Exception if helper does not have a direct() method     */    public function __call($method, $args)    {        $helper = $this->getHelper($method);        if (!method_exists($helper, 'direct')) {            require_once 'Zend/Controller/Action/Exception.php';            throw new Zend_Controller_Action_Exception('Helper "' . $method . '" does not support overloading via direct()');        }        return call_user_func_array(array($helper, 'direct'), $args);    }    /**     * Retrieve helper by name as object property     *     * @param  string $name     * @return Zend_Controller_Action_Helper_Abstract     */    public function __get($name)    {        return $this->getHelper($name);    }    /**     * Normalize helper name for lookups     *     * @param  string $name     * @return string     */    protected static function _normalizeHelperName($name)    {        if (strpos($name, '_') !== false) {            $name = str_replace(' ', '', ucwords(str_replace('_', ' ', $name)));        }        return ucfirst($name);    }    /**     * Load a helper     *     * @param  string $name     * @return void     */    protected static function _loadHelper($name)    {        try {            $class = self::getPluginLoader()->load($name);        } catch (Zend_Loader_PluginLoader_Exception $e) {            require_once 'Zend/Controller/Action/Exception.php';            throw new Zend_Controller_Action_Exception('Action Helper by name ' . $name . ' not found', 0, $e);        }        $helper = new $class();        if (!$helper instanceof Zend_Controller_Action_Helper_Abstract) {            require_once 'Zend/Controller/Action/Exception.php';            throw new Zend_Controller_Action_Exception('Helper name ' . $name . ' -> class ' . $class . ' is not of type Zend_Controller_Action_Helper_Abstract');        }        self::getStack()->push($helper);    }}

助手經紀人的常見用法：
一、注冊一個助手
1.Zend_Controller_Action_HelperBroker::addHelper($helper);
2.通過addPrefix()方法帶有一個類前綴參數，用來加入自定義助手類的路徑。
要求前綴遵循Zend Framework的類命名慣例。 
// Add helpers prefixed with My_Action_Helpers in My/Action/Helpers/
Zend_Controller_Action_HelperBroker::addPrefix('My_Action_Helpers');
3.使用addPath()方法第一個參數為一個目錄，第二個為類前綴(默認為'Zend_Controller_Action_Helper')。
用來將自己的類前綴映射到指定的目錄。 
// Add helpers prefixed with Helper in Plugins/Helpers/
Zend_Controller_Action_HelperBroker::addPath('./Plugins/Helpers',
                                             'Helper');


二、判讀助手是否存在
使用hasHelper($name)方法來判定助手經紀人中是否存在某助手，$name是助手的短名稱（去掉前綴的）： 


// Check if 'redirector' helper is registered with the broker:
if (Zend_Controller_Action_HelperBroker::hasHelper('redirector')) {
    echo 'Redirector helper registered';
}


從助手經紀人中獲取助手有兩個靜態方法：getExistingHelper() 和 getStaticHelper() 。getExistingHelper()將獲取助手僅當它以前調用過或者顯性地通過助手經紀人注冊過，否則就拋出一個異常。getStaticHelper() 的做法和getExistingHelper()一樣，但如果還沒有注冊助手堆棧，它將嘗試初始化助手，為獲取你要配置的的助手，getStaticHelper()是一個好的選擇。 


兩個方法都帶一個參數，$name，它是助手的短名稱（去掉前綴）。 


// Check if 'redirector' helper is registered with the broker, and fetch:
if (Zend_Controller_Action_HelperBroker::hasHelper('redirector')) {
    $redirector =
        Zend_Controller_Action_HelperBroker::getExistingHelper('redirector');
}


// Or, simply retrieve it, not worrying about whether or not it was
// previously registered:
$redirector =
    Zend_Controller_Action_HelperBroker::getStaticHelper('redirector');
}
三、removeHelper($name)刪除助手經紀人中的某個助手，$name是助手的短名稱。 


// Conditionally remove the 'redirector' helper from the broker:
if (Zend_Controller_Action_HelperBroker::hasHelper('redirector')) {
    Zend_Controller_Action_HelperBroker::removeHelper('redirector')
}


下面介紹如何自定義助手。