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• 原文作者：
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• 翻译人员：FireHare
• 校对人员：FireHare
• 适用版本：Symfony 2.1
• 文章状态：草译阶段

The main motivation for writing an extension is to move often used code into a reusable class like adding support for internationalization. An extension can define tags, filters, tests, operators, global variables, functions, and node visitors.

创建扩展的主要目的是将常用代码移入一个可复用的类中，如添加国际化支持那样。一个扩展可以定义标签、过滤器、测试、操作、全局变量、函数和节点访问等。

Creating an extension also makes for a better separation of code that is executed at compilation time and code needed at runtime. As such, it makes your code faster.

创建扩展还可以有效地分隔编译时和运行时代码。这样它可以让您的代码运行地更快。

Before writing your own extensions, have a look at the . 在创建您自己的扩展之前，请先看一下

 

Create the Extension Class

创建扩展类

To get your custom functionality you must first create a Twig Extension class. As an example we will create a price filter to format a given number into price:

要实现定制功能，您首先必须创建一个Twig扩展类。作为示例，我们将创建一个价格过滤器，用以将给定数字转成价格格式：

1. // src/Acme/DemoBundle/Twig/AcmeExtension.php 
2. namespace Acme\DemoBundle\Twig; 
3.  
4. use Twig_Extension; 
5. use Twig_Filter_Method; 
6.  
7. class AcmeExtension extends Twig_Extension 
8. { 
9.     public function getFilters() 
10.     { 
11.         return array( 
12.             'price' => new Twig_Filter_Method($this, 'priceFilter'), 
13.         ); 
14.     } 
15.  
16.     public function priceFilter($number, $decimals = 0, $decPoint = '.', $thousandsSep = ',') 
17.     { 
18.         $price = number_format($number, $decimals, $decPoint, $thousandsSep); 
19.         $price = '$' . $price; 
20.  
21.         return $price; 
22.     } 
23.  
24.     public function getName() 
25.     { 
26.         return 'acme_extension'; 
27.     } 
28. } 

Along with custom filters, you can also add custom functions and register global variables. 除了定制过滤器，您还可以添加定制函数和注册全局变量。

 

Register an Extension as a Service

注册扩展服务

Now you must let Service Container know about your newly created Twig Extension:

现在您必须让服务容器知道您新建的Twig扩展：

1. <!-- src/Acme/DemoBundle/Resources/config/services.xml --> 
2. <services> 
3.     <service id="acme.twig.acme_extension" class="Acme\DemoBundle\Twig\AcmeExtension"> 
4.         <tag name="twig.extension" /> 
5.     </service> 
6. </services> 

Keep in mind that Twig Extensions are not lazily loaded. This means that there's a higher chance that you'll get a CircularReferenceException or a ScopeWideningInjectionException if any services (or your Twig Extension in this case) are dependent on the request service. For more information take a look at . 记住，Twig扩展并非被延迟加载。这就意味着如果您的服务（或本例中的Twig扩展）依赖request服务的话，您将有更高的几率得到CircularReferenceException 或 ScopeWideningInjectionException 异常。详情请参见.

 

Using the custom Extension

使用定制扩展

Using your newly created Twig Extension is no different than any other:

使用您新建的Twig扩展与其它的没什么不同：

1. {# outputs $5,500.00 #} 
2. {
   { '5500'|price }} 

Passing other arguments to your filter:

发送其它参数到您的过滤器：

1. {# outputs $5500,2516 #} 
2. {
   { '5500.25155'|price(4, ',', '') }}