Symfony2CookBook：如何定制模板扩展

• 原文出处：http://symfony.com/doc/current/cookbook/templating/twig_extension.html
• 原文作者：symfony.com
• 授权许可：创作共用协议
• 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 Twig official extension repository. 在创建您自己的扩展之前，请先看一下Twig官方扩展库

 

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：

// src/Acme/DemoBundle/Twig/AcmeExtension.php
namespace Acme\DemoBundle\Twig;

use Twig_Extension;
use Twig_Filter_Method;

class AcmeExtension extends Twig_Extension
{
    public function getFilters()
    {
        return array(
            'price' => new Twig_Filter_Method($this, 'priceFilter'),
        );
    }

    public function priceFilter($number, $decimals = 0, $decPoint = '.', $thousandsSep = ',')
    {
        $price = number_format($number, $decimals, $decPoint, $thousandsSep);
        $price = '$' . $price;

        return $price;
    }

    public function getName()
    {
        return 'acme_extension';
    }
}

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：

<!-- src/Acme/DemoBundle/Resources/config/services.xml -->
<services>
    <service id="acme.twig.acme_extension" class="Acme\DemoBundle\Twig\AcmeExtension">
        <tag name="twig.extension" />
    </service>
</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 How to work with Scopes. 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。详情请参见如何使用范围.

 

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：

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

Passing other arguments to your filter:
发送其它参数到您的过滤器：

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

Learning further
进一步学习

For a more in-depth look into Twig Extensions, please take a look at the Twig extensions documentation.
要更深入地了解Twig扩展，请查看Twig扩展文档。