* * * * *
[TOC]
## 简介
Laravel 的契约是一组定义框架提供的核心服务的接口。例如，`Illuminate\Contracts\Queue\Queue` 契约定义了队列任务所需的方法，而 `Illuminate\Contracts\Mail\Mailer` 契约定义了发送电子邮件所需的方法。
框架对每个契约都提供了相应的实现。例如，Laravel 提供了具有各种驱动的队列实现和由 [SwiftMailer](https://swiftmailer.symfony.com/) 提供支持的邮件驱动实现。
所有的 Laravel 契约都有 [他们自己的 GitHub 库](https://github.com/illuminate/contracts)。这为所有可用的契约提供了一个快速参考指南，同时也可单独作为低耦合的扩展包给其他包开发者使用。
### 契约 VS Facades
Laravel [Facades](https://www.kancloud.cn/tonyyu/laravel_5_6/786058) 和辅助函数提供了一种使用 Laravel 服务的简单方法，即不需要通过类型提示并从服务容器中解析契约。在大多数情况下，每个 Facades 都有一个等效的契约。
不像 Facades，不需要你在类的构造函数中类型提示，契约则需要你在类中明显地定义依赖项。一些开发者倾向于以契约这种方式明确地定义它们的依赖项，而其它开发者则更喜欢 Facades 带来的便捷。
> {tip} 对于大多数应用程序来说不管是使用 facades 还是契约都可以。但是，如果你正在构建一个扩展包，为了方便测试，你应该强烈考虑契约。
## 何时使用契约
综上所述，使用契约或是 Facades 很大程度上归结于个人或者开发团队的喜好。不管是契约还是 Facades 都可以创建出健壮的、易测试的 Laravel 应用程序。如果你长期关注类的单一职责，你会注意到使用契约还是 Facades 其实没多少实际意义上的区别。
然而，你可能还是会有几个关于契约的问题。例如，为什么要使用接口？不使用接口会比较复杂吗？下面让我们谈下使用接口的原因：低耦合和简单性。
### 低耦合
首先，让我们来看一些高耦合缓存实现的代码。如下:
~~~
<?php
namespace App\Orders;
class Repository
{
/**
* 缓存实例。
*/
protected $cache;
/**
* 创建一个仓库实例。
*
* @param \SomePackage\Cache\Memcached $cache
* @return void
*/
public function __construct(\SomePackage\Cache\Memcached $cache)
{
$this->cache = $cache;
}
/**
* 按照 Id 检索订单
*
* @param int $id
* @return Order
*/
public function find($id)
{
if ($this->cache->has($id)) {
//
}
}
}
~~~
在这个类中，程序跟给定的缓存实现高耦合。因为我们依赖于一个扩展包的特定缓存类。一旦这个扩展包的 API 被更改了，我们的代码就必须跟着改变。
同样的，如果我们想要将底层的的缓存技术（ Memcached ）替换为另一种缓存技术（ Redis ），那又得再次修改这个 Repository 类。而 Repository 类不应该了解太多关于谁提供了这些数据或是如何提供的等等。
**比起上面的做法，我们可以使用一个简单的、与扩展包无关的接口来改进我们的代码：**
~~~
<?php
namespace App\Orders;
use Illuminate\Contracts\Cache\Repository as Cache;
class Repository
{
/**
* 缓存实例。
*/
protected $cache;
/**
* 创建一个仓库实例。
*
* @param Cache $cache
* @return void
*/
public function __construct(Cache $cache)
{
$this->cache = $cache;
}
}
~~~
现在，更改之后的代码没有与任何扩展包甚至是 Laravel 耦合。而契约扩展包不包含任何实现和依赖项，你可以轻松地写任何给定契约的替代实现，来实现不修改任何关于缓存消耗的代码就可以替换缓存实现。
### 简单性
当所有 Laravel 的服务都使用简洁的接口定义，就很容易判断给定服务提供的功能。 **可以将契约视为说明框架功能的简洁文档。**
除此之外，当依赖的接口足够简洁时，代码的可读性和可维护性会大大提高。比起搜索一个大型复杂的类中有哪些可用的方法，不如检索一个简单、 干净的接口来参考更妥当。
## 如何使用契约
那么，如何获得一个契约的实现呢？这其实很简单。
Laravel 中的许多类型的类都是通过 [服务容器](https://www.kancloud.cn/tonyyu/laravel_5_6/786056) 解析出来的，包括控制器、事件监听器、中间件、任务队列，甚至路由闭包。所以说，要获得一个契约的实现，你只需要被解析的类的构造函数中添加「类型提示」即可。
例如，看看这个事件监听器：
~~~
<?php
namespace App\Listeners;
use App\User;
use App\Events\OrderWasPlaced;
use Illuminate\Contracts\Redis\Database;
class CacheOrderInformation
{
/**
* Redis 数据库实现。
*/
protected $redis;
/**
* 创建事件处理器实例。
*
* @param Database $redis
* @return void
*/
public function __construct(Database $redis)
{
$this->redis = $redis;
}
/**
* 处理事件。
*
* @param OrderWasPlaced $event
* @return void
*/
public function handle(OrderWasPlaced $event)
{
//
}
}
~~~
当事件监听器被解析时，服务容器会读取类的构造函数上的类型提示，并注入对应的值。想了解更多关于服务容器的注册，请查看 [这个文档](https://www.kancloud.cn/tonyyu/laravel_5_6/786056)。
## 契约参考
下表提供了所有 Laravel 契约及其对应的 Facades：
| 契约 | 参考 Facade |
| --- | --- |
| [Illuminate\Contracts\Auth\Access\Authorizable](https://github.com/illuminate/contracts/blob/laravel/5.6/Auth/Access/Authorizable.php) | |
| [Illuminate\Contracts\Auth\Access\Gate](https://github.com/illuminate/contracts/blob/laravel/5.6/Auth/Access/Gate.php) | `Gate` |
| [Illuminate\Contracts\Auth\Authenticatable](https://github.com/illuminate/contracts/blob/laravel/5.6/Auth/Authenticatable.php) | |
| [Illuminate\Contracts\Auth\CanResetPassword](https://github.com/illuminate/contracts/blob/laravel/5.6/Auth/CanResetPassword.php) | |
| [Illuminate\Contracts\Auth\Factory](https://github.com/illuminate/contracts/blob/laravel/5.6/Auth/Factory.php) | `Auth` |
| [Illuminate\Contracts\Auth\Guard](https://github.com/illuminate/contracts/blob/laravel/5.6/Auth/Guard.php) | `Auth::guard()` |
| [Illuminate\Contracts\Auth\PasswordBroker](https://github.com/illuminate/contracts/blob/laravel/5.6/Auth/PasswordBroker.php) | `Password::broker()` |
| [Illuminate\Contracts\Auth\PasswordBrokerFactory](https://github.com/illuminate/contracts/blob/laravel/5.6/Auth/PasswordBrokerFactory.php) | `Password` |
| [Illuminate\Contracts\Auth\StatefulGuard](https://github.com/illuminate/contracts/blob/laravel/5.6/Auth/StatefulGuard.php) | |
| [Illuminate\Contracts\Auth\SupportsBasicAuth](https://github.com/illuminate/contracts/blob/laravel/5.6/Auth/SupportsBasicAuth.php) | |
| [Illuminate\Contracts\Auth\UserProvider](https://github.com/illuminate/contracts/blob/laravel/5.6/Auth/UserProvider.php) | |
| [Illuminate\Contracts\Bus\Dispatcher](https://github.com/illuminate/contracts/blob/laravel/5.6/Bus/Dispatcher.php) | `Bus` |
| [Illuminate\Contracts\Bus\QueueingDispatcher](https://github.com/illuminate/contracts/blob/laravel/5.6/Bus/QueueingDispatcher.php) | `Bus::dispatchToQueue()` |
| [Illuminate\Contracts\Broadcasting\Factory](https://github.com/illuminate/contracts/blob/laravel/5.6/Broadcasting/Factory.php) | `Broadcast` |
| [Illuminate\Contracts\Broadcasting\Broadcaster](https://github.com/illuminate/contracts/blob/laravel/5.6/Broadcasting/Broadcaster.php) | `Broadcast::connection()` |
| [Illuminate\Contracts\Broadcasting\ShouldBroadcast](https://github.com/illuminate/contracts/blob/laravel/5.6/Broadcasting/ShouldBroadcast.php) | |
| [Illuminate\Contracts\Broadcasting\ShouldBroadcastNow](https://github.com/illuminate/contracts/blob/laravel/5.6/Broadcasting/ShouldBroadcastNow.php) | |
| [Illuminate\Contracts\Cache\Factory](https://github.com/illuminate/contracts/blob/laravel/5.6/Cache/Factory.php) | `Cache` |
| [Illuminate\Contracts\Cache\Lock](https://github.com/illuminate/contracts/blob/laravel/5.6/Cache/Lock.php) | |
| [Illuminate\Contracts\Cache\LockProvider](https://github.com/illuminate/contracts/blob/laravel/5.6/Cache/LockProvider.php) | |
| [Illuminate\Contracts\Cache\Repository](https://github.com/illuminate/contracts/blob/laravel/5.6/Cache/Repository.php) | `Cache::driver()` |
| [Illuminate\Contracts\Cache\Store](https://github.com/illuminate/contracts/blob/laravel/5.6/Cache/Store.php) | |
| [Illuminate\Contracts\Config\Repository](https://github.com/illuminate/contracts/blob/laravel/5.6/Config/Repository.php) | `Config` |
| [Illuminate\Contracts\Console\Application](https://github.com/illuminate/contracts/blob/laravel/5.6/Console/Application.php) | |
| [Illuminate\Contracts\Console\Kernel](https://github.com/illuminate/contracts/blob/laravel/5.6/Console/Kernel.php) | `Artisan` |
| [Illuminate\Contracts\Container\Container](https://github.com/illuminate/contracts/blob/laravel/5.6/Container/Container.php) | `App` |
| [Illuminate\Contracts\Cookie\Factory](https://github.com/illuminate/contracts/blob/laravel/5.6/Cookie/Factory.php) | `Cookie` |
| [Illuminate\Contracts\Cookie\QueueingFactory](https://github.com/illuminate/contracts/blob/laravel/5.6/Cookie/QueueingFactory.php) | `Cookie::queue()` |
| [Illuminate\Contracts\Database\ModelIdentifier](https://github.com/illuminate/contracts/blob/laravel/5.6/Database/ModelIdentifier.php) | |
| [Illuminate\Contracts\Debug\ExceptionHandler](https://github.com/illuminate/contracts/blob/laravel/5.6/Debug/ExceptionHandler.php) | |
| [Illuminate\Contracts\Encryption\Encrypter](https://github.com/illuminate/contracts/blob/laravel/5.6/Encryption/Encrypter.php) | `Crypt` |
| [Illuminate\Contracts\Events\Dispatcher](https://github.com/illuminate/contracts/blob/laravel/5.6/Events/Dispatcher.php) | `Event` |
| [Illuminate\Contracts\Filesystem\Cloud](https://github.com/illuminate/contracts/blob/laravel/5.6/Filesystem/Cloud.php) | `Storage::cloud()` |
| [Illuminate\Contracts\Filesystem\Factory](https://github.com/illuminate/contracts/blob/laravel/5.6/Filesystem/Factory.php) | `Storage` |
| [Illuminate\Contracts\Filesystem\Filesystem](https://github.com/illuminate/contracts/blob/laravel/5.6/Filesystem/Filesystem.php) | `Storage::disk()` |
| [Illuminate\Contracts\Foundation\Application](https://github.com/illuminate/contracts/blob/laravel/5.6/Foundation/Application.php) | `App` |
| [Illuminate\Contracts\Hashing\Hasher](https://github.com/illuminate/contracts/blob/laravel/5.6/Hashing/Hasher.php) | `Hash` |
| [Illuminate\Contracts\Http\Kernel](https://github.com/illuminate/contracts/blob/laravel/5.6/Http/Kernel.php) | |
| [Illuminate\Contracts\Logging\Log](https://github.com/illuminate/contracts/blob/laravel/5.6/Logging/Log.php) | `Log` |
| [Illuminate\Contracts\Mail\MailQueue](https://github.com/illuminate/contracts/blob/laravel/5.6/Mail/MailQueue.php) | `Mail::queue()` |
| [Illuminate\Contracts\Mail\Mailable](https://github.com/illuminate/contracts/blob/laravel/5.6/Mail/Mailable.php) | |
| [Illuminate\Contracts\Mail\Mailer](https://github.com/illuminate/contracts/blob/laravel/5.6/Mail/Mailer.php) | `Mail` |
| [Illuminate\Contracts\Notifications\Dispatcher](https://github.com/illuminate/contracts/blob/laravel/5.6/Notifications/Dispatcher.php) | `Notification` |
| [Illuminate\Contracts\Notifications\Factory](https://github.com/illuminate/contracts/blob/laravel/5.6/Notifications/Factory.php) | `Notification` |
| [Illuminate\Contracts\Pagination\LengthAwarePaginator](https://github.com/illuminate/contracts/blob/laravel/5.6/Pagination/LengthAwarePaginator.php) | |
| [Illuminate\Contracts\Pagination\Paginator](https://github.com/illuminate/contracts/blob/laravel/5.6/Pagination/Paginator.php) | |
| [Illuminate\Contracts\Pipeline\Hub](https://github.com/illuminate/contracts/blob/laravel/5.6/Pipeline/Hub.php) | |
| [Illuminate\Contracts\Pipeline\Pipeline](https://github.com/illuminate/contracts/blob/laravel/5.6/Pipeline/Pipeline.php) | |
| [Illuminate\Contracts\Queue\EntityResolver](https://github.com/illuminate/contracts/blob/laravel/5.6/Queue/EntityResolver.php) | |
| [Illuminate\Contracts\Queue\Factory](https://github.com/illuminate/contracts/blob/laravel/5.6/Queue/Factory.php) | `Queue` |
| [Illuminate\Contracts\Queue\Job](https://github.com/illuminate/contracts/blob/laravel/5.6/Queue/Job.php) | |
| [Illuminate\Contracts\Queue\Monitor](https://github.com/illuminate/contracts/blob/laravel/5.6/Queue/Monitor.php) | `Queue` |
| [Illuminate\Contracts\Queue\Queue](https://github.com/illuminate/contracts/blob/laravel/5.6/Queue/Queue.php) | `Queue::connection()` |
| [Illuminate\Contracts\Queue\QueueableCollection](https://github.com/illuminate/contracts/blob/laravel/5.6/Queue/QueueableCollection.php) | |
| [Illuminate\Contracts\Queue\QueueableEntity](https://github.com/illuminate/contracts/blob/laravel/5.6/Queue/QueueableEntity.php) | |
| [Illuminate\Contracts\Queue\ShouldQueue](https://github.com/illuminate/contracts/blob/laravel/5.6/Queue/ShouldQueue.php) | |
| [Illuminate\Contracts\Redis\Factory](https://github.com/illuminate/contracts/blob/laravel/5.6/Redis/Factory.php) | `Redis` |
| [Illuminate\Contracts\Routing\BindingRegistrar](https://github.com/illuminate/contracts/blob/laravel/5.6/Routing/BindingRegistrar.php) | `Route` |
| [Illuminate\Contracts\Routing\Registrar](https://github.com/illuminate/contracts/blob/laravel/5.6/Routing/Registrar.php) | `Route` |
| [Illuminate\Contracts\Routing\ResponseFactory](https://github.com/illuminate/contracts/blob/laravel/5.6/Routing/ResponseFactory.php) | `Response` |
| [Illuminate\Contracts\Routing\UrlGenerator](https://github.com/illuminate/contracts/blob/laravel/5.6/Routing/UrlGenerator.php) | `URL` |
| [Illuminate\Contracts\Routing\UrlRoutable](https://github.com/illuminate/contracts/blob/laravel/5.6/Routing/UrlRoutable.php) | |
| [Illuminate\Contracts\Session\Session](https://github.com/illuminate/contracts/blob/laravel/5.6/Session/Session.php) | `Session::driver()` |
| [Illuminate\Contracts\Support\Arrayable](https://github.com/illuminate/contracts/blob/laravel/5.6/Support/Arrayable.php) | |
| [Illuminate\Contracts\Support\Htmlable](https://github.com/illuminate/contracts/blob/laravel/5.6/Support/Htmlable.php) | |
| [Illuminate\Contracts\Support\Jsonable](https://github.com/illuminate/contracts/blob/laravel/5.6/Support/Jsonable.php) | |
| [Illuminate\Contracts\Support\MessageBag](https://github.com/illuminate/contracts/blob/laravel/5.6/Support/MessageBag.php) | |
| [Illuminate\Contracts\Support\MessageProvider](https://github.com/illuminate/contracts/blob/laravel/5.6/Support/MessageProvider.php) | |
| [Illuminate\Contracts\Support\Renderable](https://github.com/illuminate/contracts/blob/laravel/5.6/Support/Renderable.php) | |
| [Illuminate\Contracts\Support\Responsable](https://github.com/illuminate/contracts/blob/laravel/5.6/Support/Responsable.php) | |
| [Illuminate\Contracts\Translation\Loader](https://github.com/illuminate/contracts/blob/laravel/5.6/Translation/Loader.php) | |
| [Illuminate\Contracts\Translation\Translator](https://github.com/illuminate/contracts/blob/laravel/5.6/Translation/Translator.php) | `Lang` |
| [Illuminate\Contracts\Validation\Factory](https://github.com/illuminate/contracts/blob/laravel/5.6/Validation/Factory.php) | `Validator` |
| [Illuminate\Contracts\Validation\ImplicitRule](https://github.com/illuminate/contracts/blob/laravel/5.6/Validation/ImplicitRule.php) | |
| [Illuminate\Contracts\Validation\Rule](https://github.com/illuminate/contracts/blob/laravel/5.6/Validation/Rule.php) | |
| [Illuminate\Contracts\Validation\ValidatesWhenResolved](https://github.com/illuminate/contracts/blob/laravel/5.6/Validation/ValidatesWhenResolved.php) | |
| [Illuminate\Contracts\Validation\Validator](https://github.com/illuminate/contracts/blob/laravel/5.6/Validation/Validator.php) | `Validator::make()` |
| [Illuminate\Contracts\View\Engine](https://github.com/illuminate/contracts/blob/laravel/5.6/View/Engine.php) | |
| [Illuminate\Contracts\View\Factory](https://github.com/illuminate/contracts/blob/laravel/5.6/View/Factory.php) | `View` |
| [Illuminate\Contracts\View\View](https://github.com/illuminate/contracts/blob/laravel/5.6/View/View.php) | `View::make()` |
- 前言
- 翻译说明
- 发行说明
- 升级指南
- 贡献导引
- 入门指南
- 安装
- 配置信息
- 文件夹结构
- Homestead
- Valet
- 部署
- 核心架构
- 请求周期
- 服务容器
- 服务提供者
- Facades
- Contracts
- 基础功能
- 路由
- 中间件
- CSRF 保护
- 控制器
- 请求
- 响应
- 视图
- URL
- Session
- 表单验证
- 错误
- 日志
- 前端开发
- Blade 模板
- 本地化
- 前端指南
- 编辑资源 Mix
- 安全相关
- 用户认证
- Passport OAuth 认证
- 用户授权
- 加密解密
- 哈希
- 重置密码
- 综合话题
- Artisan 命令行
- 广播系统
- 缓存系统
- 集合
- 事件系统
- 文件存储
- 辅助函数
- 邮件发送
- 消息通知
- 扩展包开发
- 队列
- 任务调度
- 数据库
- 快速入门
- 查询构造器
- 分页
- 数据库迁移
- 数据填充
- Redis
- Eloquent ORM
- 快速入门
- 模型关联
- Eloquent 集合
- 修改器
- API 资源
- 序列化
- 测试相关
- 快速入门
- HTTP 测试
- 浏览器测试 Dusk
- 数据库测试
- 测试模拟器
- 官方扩展包
- Cashier 交易工具包
- Envoy 部署工具
- Horizon
- Scout 全文搜索
- Socialite 社会化登录