使用Yii2依赖注入简化开发

本文代码

https://github.com/xialeistudio/yii2-di-demo

什么是依赖注入(DI)?

对象由框架来创建而不是程序员通过 new 创建。跟IoC差不多一个意思。

为什么要有依赖注入?

1. 解耦。调用方不再通过 new 运算符实例化被调用对象，而通过框架(IoC容器)创建之后注入进来。解除了调用者与被调用者之间的依赖。
2. 有利于面向接口编程。个人认为OOP程序设计最重要的就是面向接口(面向抽象)编程。因为有了第1步的关系，调用者只需要依赖接口类型而不用依赖实现类型，提高了程序的扩展性。

Yii2的依赖注入

Yii2通过 yiidiContainer 提供DI容器特性。目前支持一下4种方式注入：

1. 构造方法注入
2. 方法注入
3. Setter和属性注入
4. PHP回调注入

注册依赖关系

1. 通过容器的 set 方法注入
2. 通过配置文件注入(推荐)

依赖注入实战

1. 打开终端，执行以下命令初始化项目：

   composer create-project --prefer-dist yiisoft/yii2-app-basic basic

2. 声明接口业务类 appservicesUserService

   <?php
   namespace app\services;
   
   interface UserService
   {
       public function show($id);
       
       public function all();
   }

3. 接口实现文件 appservicesimplUserServiceImpl

   <?php
   namespace app\services\impl;
   
   use app\services\UserService;
   
   class UserServiceImpl implements UserService
   {
       private $users = [
           ['id' => 1, 'name' => 'xialei'],
           ['id' => 2, 'name' => 'zhangsan'],
       ];
   
       public function show($id)
       {
           foreach ($this->users as $user) {
               if ($user['id'] == $id) {
                   return $user;
               }
           }
           return null;
       }
   
       public function all()
       {
           return $this->users;
       }
   }

4. 注册依赖关系 config/web.php

   <?php
   
   use app\services\UserService;
   use app\services\impl\UserServiceImpl;
   
   $params = require __DIR__ . '/params.php';
   $db = require __DIR__ . '/db.php';
   
   $config = [
       'id' => 'basic',
       'basePath' => dirname(__DIR__),
       'bootstrap' => ['log'],
       'aliases' => [
           '@bower' => '@vendor/bower-asset',
           '@npm' => '@vendor/npm-asset',
       ],
       'container' => [
           'definitions' => [
               UserService::class => UserServiceImpl::class
           ]
       ],
       'components' => [
           'request' => [
               // !!! insert a secret key in the following (if it is empty) - this is required by cookie validation
               'cookieValidationKey' => '0xGrStOOZE2oXxNNiu-o2eYovJ_Ia1Dk',
           ],
           'response' => [
               'format' => 'json'
           ],
           'errorHandler' => [
               'errorAction' => 'site/error',
           ],
           'urlManager' => [
               'enablePrettyUrl' => true,
               'showScriptName' => false,
               'rules' => [
               ],
           ],
       ],
   ];
   
   if (YII_ENV_DEV) {
       // configuration adjustments for 'dev' environment
       $config['bootstrap'][] = 'debug';
       $config['modules']['debug'] = [
           'class' => 'yii\debug\Module',
           // uncomment the following to add your IP if you are not connecting from localhost.
           //'allowedIPs' => ['127.0.0.1', '::1'],
       ];
   
       $config['bootstrap'][] = 'gii';
       $config['modules']['gii'] = [
           'class' => 'yii\gii\Module',
           // uncomment the following to add your IP if you are not connecting from localhost.
           //'allowedIPs' => ['127.0.0.1', '::1'],
       ];
   }
   
   return $config;

5. 添加控制器 appcontrollersUserController

   <?php
   
   namespace app\controllers;
   
   use app\services\UserService;
   use yii\base\Module;
   use yii\web\Controller;
   use yii\web\NotFoundHttpException;
   
   class UserController extends Controller
   {
       private $userService;
   
       public function __construct(string $id, Module $module, UserService $userService, array $config = [])
       {
           $this->userService = $userService;
           parent::__construct($id, $module, $config);
       }
   
       public function actionShow($id)
       {
           $user = $this->userService->show($id);
           if (empty($user)) {
               throw new NotFoundHttpException('用户不存在');
           }
           return $user;
       }
       
       public function actionAll()
       {
           return $this->userService->all();
       }
   }

6. 运行测试服务器

   ./yii serve/index

7. 访问用户列表接口 http://localhost:8080/user/all

   [{
       "id": 1,
       "name": "xialei"
   }, {
       "id": 2,
       "name": "zhangsan"
   }]

8. 访问查看用户接口 http://localhost:8080/user/show?id=1

   {
       "id": 1,
       "name": "xialei"
   }

写在最后

如你所见，Yii2自带的IoC容器使用起来还是挺方便的，观测了Yii 配置优于编码 的思想，Yii的组件基本上都可以在配置文件中进行配置而不需要手动编码。

灵活使用DI可以使我们从依赖关系中解脱出来，专注于业务逻辑。

当然，业务逻辑的组织也是一个很大的研究课题，有兴趣的可以去看看 DDD(领域驱动设计)