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

通过助手模式，可以把一些经常使用的功能模块做封装，从而在可以在需要的地方灵活使用，主要是在action使用。
Zend Framework中有两种助手，动作助手(Zend_Controller_Action_Helper)和试图助手(Zend_View_Helper)。
动作助手可以向任何Zend_Controller_Action的衍生动作控制器中，即时的加入功能(runtime and/or on-demand functionality)，以使得增加公共的动作控制器功能时，尽量减少衍生动作控制器类的必要。 
动作助手在需要调用时加载，可以在请求的时候(bootstrap)或者动作控制器创建的时候(init())实例化。


涉及到的相关文件
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


常见的动作助手有：
FlashMessenger 用来处理Flash Messenger会话；
Json 用来解码和发送 JSON 响应；
Url  用于创建Urls；
Redirector 提供另一种实现方式，帮助程序重定向到内部或者外部页面；
ViewRenderer 自动的完成在控制器内建立视图对象并渲染视图的过程；
AutoComplete 自动响应 AJAX 的自动完成；
ContextSwitch 和 AjaxContext 为你的动作提供替代响应格式；
Cache  实现cache的相关操作；
ActionStack 用于操作动作堆栈。


动手的几种实例化使用方式
1.通过Zend_Controller_Action的 $_helper成员的getHelper()方法。直接调用getHelper()，传入助手的名称即可。


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


2.直接通过访问的_helper助手的属性对应的助手对象。
$redirector = $this->_helper->Redirector;




Zend_Controller_Action_HelperBroker
中文名称译作"助手经纪人",顾名思义，是动作助手的中间人。
在动作的实例化使用的方式的第二种方式就是通过Zend_Controller_Action_HelperBroker的魔术方法__get()来实现的。
助手经纪人用于注册助手对象和助手路径以及获取助手等等功能。 


Zend_Controller_Action_HelperBroker的实现以及常用方法列表

<?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);    }}

助手经纪人的常见用法：
一、注册一个助手
1.Zend_Controller_Action_HelperBroker::addHelper($helper);
2.通过addPrefix()方法带有一个类前缀参数，用来加入自定义助手类的路径。
要求前缀遵循Zend Framework的类命名惯例。 
// Add helpers prefixed with My_Action_Helpers in My/Action/Helpers/
Zend_Controller_Action_HelperBroker::addPrefix('My_Action_Helpers');
3.使用addPath()方法第一个参数为一个目录，第二个为类前缀(默认为'Zend_Controller_Action_Helper')。
用来将自己的类前缀映射到指定的目录。 
// Add helpers prefixed with Helper in Plugins/Helpers/
Zend_Controller_Action_HelperBroker::addPath('./Plugins/Helpers',
                                             'Helper');


二、判读助手是否存在
使用hasHelper($name)方法来判定助手经纪人中是否存在某助手，$name是助手的短名称（去掉前缀的）： 


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


从助手经纪人中获取助手有两个静态方法：getExistingHelper() 和 getStaticHelper() 。getExistingHelper()将获取助手仅当它以前调用过或者显性地通过助手经纪人注册过，否则就抛出一个异常。getStaticHelper() 的做法和getExistingHelper()一样，但如果还没有注册助手堆栈，它将尝试初始化助手，为获取你要配置的的助手，getStaticHelper()是一个好的选择。 


两个方法都带一个参数，$name，它是助手的短名称（去掉前缀）。 


// 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)删除助手经纪人中的某个助手，$name是助手的短名称。 


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


下面介绍如何自定义助手。