Laravel之Contracts和Facades详解

Contracts其实就是倡导面向接口编程，来达到解耦的目的。而这些通用的接口已经由Laravel为你设计好了。就是这些Contracts.

那么Laravel如何知道我们需要使用哪个实现呢？

在Laravel默认的Contracts绑定中，在’Illuminate/Foundation/Application.php’有这样的定义:这就是绑定了默认的接口实现.

推荐：《laravel教程》

/**
     * Register the core class aliases in the container.
     *
     * @return void
     */
    public function registerCoreContainerAliases()
    {
        $aliases = [
            'app'                  => ['Illuminate\Foundation\Application', 'Illuminate\Contracts\Container\Container', 'Illuminate\Contracts\Foundation\Application'],
            'auth'                 => 'Illuminate\Auth\AuthManager',
            'auth.driver'          => ['Illuminate\Auth\Guard', 'Illuminate\Contracts\Auth\Guard'],
            'auth.password.tokens' => 'Illuminate\Auth\Passwords\TokenRepositoryInterface',
            'blade.compiler'       => 'Illuminate\View\Compilers\BladeCompiler',
            'cache'                => ['Illuminate\Cache\CacheManager', 'Illuminate\Contracts\Cache\Factory'],
            'cache.store'          => ['Illuminate\Cache\Repository', 'Illuminate\Contracts\Cache\Repository'],
            'config'               => ['Illuminate\Config\Repository', 'Illuminate\Contracts\Config\Repository'],
            'cookie'               => ['Illuminate\Cookie\CookieJar', 'Illuminate\Contracts\Cookie\Factory', 'Illuminate\Contracts\Cookie\QueueingFactory'],
            'encrypter'            => ['Illuminate\Encryption\Encrypter', 'Illuminate\Contracts\Encryption\Encrypter'],
            'db'                   => 'Illuminate\Database\DatabaseManager',
            'db.connection'        => ['Illuminate\Database\Connection', 'Illuminate\Database\ConnectionInterface'],
            'events'               => ['Illuminate\Events\Dispatcher', 'Illuminate\Contracts\Events\Dispatcher'],
            'files'                => 'Illuminate\Filesystem\Filesystem',
            'filesystem'           => ['Illuminate\Filesystem\FilesystemManager', 'Illuminate\Contracts\Filesystem\Factory'],
            'filesystem.disk'      => 'Illuminate\Contracts\Filesystem\Filesystem',
            'filesystem.cloud'     => 'Illuminate\Contracts\Filesystem\Cloud',
            'hash'                 => 'Illuminate\Contracts\Hashing\Hasher',
            'translator'           => ['Illuminate\Translation\Translator', 'Symfony\Component\Translation\TranslatorInterface'],
            'log'                  => ['Illuminate\Log\Writer', 'Illuminate\Contracts\Logging\Log', 'Psr\Log\LoggerInterface'],
            'mailer'               => ['Illuminate\Mail\Mailer', 'Illuminate\Contracts\Mail\Mailer', 'Illuminate\Contracts\Mail\MailQueue'],
            'auth.password'        => ['Illuminate\Auth\Passwords\PasswordBroker', 'Illuminate\Contracts\Auth\PasswordBroker'],
            'queue'                => ['Illuminate\Queue\QueueManager', 'Illuminate\Contracts\Queue\Factory', 'Illuminate\Contracts\Queue\Monitor'],
            'queue.connection'     => 'Illuminate\Contracts\Queue\Queue',
            'redirect'             => 'Illuminate\Routing\Redirector',
            'redis'                => ['Illuminate\Redis\Database', 'Illuminate\Contracts\Redis\Database'],
            'request'              => 'Illuminate\Http\Request',
            'router'               => ['Illuminate\Routing\Router', 'Illuminate\Contracts\Routing\Registrar'],
            'session'              => 'Illuminate\Session\SessionManager',
            'session.store'        => ['Illuminate\Session\Store', 'Symfony\Component\HttpFoundation\Session\SessionInterface'],
            'url'                  => ['Illuminate\Routing\UrlGenerator', 'Illuminate\Contracts\Routing\UrlGenerator'],
            'validator'            => ['Illuminate\Validation\Factory', 'Illuminate\Contracts\Validation\Factory'],
            'view'                 => ['Illuminate\View\Factory', 'Illuminate\Contracts\View\Factory'],
        ];

在我们自定义的接口实现时，我们可以在ServiceProvider中使用进行绑定:

$this->app->bind('App\Contracts\EventPusher', 'App\Services\PusherEventPusher');

Facades

Facades 为应用程序的服务容器中可用的类提供了一个「静态」接口。Laravel 「facades」作为在服务容器内基类的「静态代理」。很难懂？

我们打开项目目录下的config/app.php，然后找到

/*
    |--------------------------------------------------------------------------
    | Class Aliases
    |--------------------------------------------------------------------------
    |
    | This array of class aliases will be registered when this application
    | is started. However, feel free to register as many as you wish as
    | the aliases are "lazy" loaded so they don't hinder performance.
    |
    */
    'aliases' => [
        'App'       => Illuminate\Support\Facades\App::class,
        'Artisan'   => Illuminate\Support\Facades\Artisan::class,
        'Auth'      => Illuminate\Support\Facades\Auth::class,
        'Blade'     => Illuminate\Support\Facades\Blade::class,
        'Bus'       => Illuminate\Support\Facades\Bus::class,
        'Cache'     => Illuminate\Support\Facades\Cache::class,
        'Config'    => Illuminate\Support\Facades\Config::class,
        'Cookie'    => Illuminate\Support\Facades\Cookie::class,
        'Crypt'     => Illuminate\Support\Facades\Crypt::class,
        'DB'        => Illuminate\Support\Facades\DB::class,
        'Eloquent'  => Illuminate\Database\Eloquent\Model::class,
        'Event'     => Illuminate\Support\Facades\Event::class,
        'File'      => Illuminate\Support\Facades\File::class,
        'Gate'      => Illuminate\Support\Facades\Gate::class,
        'Hash'      => Illuminate\Support\Facades\Hash::class,
        'Input'     => Illuminate\Support\Facades\Input::class,
        'Lang'      => Illuminate\Support\Facades\Lang::class,
        'Log'       => Illuminate\Support\Facades\Log::class,
        'Mail'      => Illuminate\Support\Facades\Mail::class,
        'Password'  => Illuminate\Support\Facades\Password::class,
        'Queue'     => Illuminate\Support\Facades\Queue::class,
        'Redirect'  => Illuminate\Support\Facades\Redirect::class,
        'Redis'     => Illuminate\Support\Facades\Redis::class,
        'Request'   => Illuminate\Support\Facades\Request::class,
        'Response'  => Illuminate\Support\Facades\Response::class,
        'Route'     => Illuminate\Support\Facades\Route::class,
        'Schema'    => Illuminate\Support\Facades\Schema::class,
        'Session'   => Illuminate\Support\Facades\Session::class,
        'Storage'   => Illuminate\Support\Facades\Storage::class,
        'URL'       => Illuminate\Support\Facades\URL::class,
        'Validator' => Illuminate\Support\Facades\Validator::class,
        'View'      => Illuminate\Support\Facades\View::class,
    ],

你是不是发现了什么？对，Facades其实就是在config/app.php中定义的一系列类的别名。只不过这些类都具有一个共同的特点，那就是继承基底 Illuminate\Support\Facades\Facade 类并实现一个方法：getFacadeAccessor返回名称。

自定义Facade

参考http://www.tutorialspoint.com/laravel/laravel_facades.htm

Step 1 −创建一个名为 TestFacadesServiceProvider的ServiceProvider ,使用如下命令即可:

php artisan make:provider TestFacadesServiceProvider

Step 2 − 创建一个底层代理类，命名为“TestFacades.php” at “App/Test”.

App/Test/TestFacades.php

<?php
namespace App\Test;
class TestFacades{
   public function testingFacades(){
      echo "Testing the Facades in Laravel.";
   }
}
?>

Step 3 − 创建一个 Facade 类 called “TestFacades.php” at “App/Test/Facades”.

App/Test/Facades/TestFacades.php

<?php
namespace app\Test\Facades;
use Illuminate\Support\Facades\Facade;
class TestFacades extends Facade{
   protected static function getFacadeAccessor() { return 'test'; }
}

Step 4 −创建一个ServiceProviders类，名为“TestFacadesServiceProviders.php” at “App/Test/Facades”.

App/Providers/TestFacadesServiceProviders.php

<?php
namespace App\Providers;
use App;
use Illuminate\Support\ServiceProvider;
class TestFacadesServiceProvider extends ServiceProvider {
   public function boot() {
      //
   }
   public function register() {
     //可以这么绑定,这需要use App;
    //  App::bind('test',function() {
    //     return new \App\Test\TestFacades;
    //  });
     
     //也可以这么绑定，推荐。这个test对应于Facade的getFacadeAccessor返回值
        $this->app->bind("test", function(){
            return new MyFoo(); //给这个Facade返回一个代理实例。所有对Facade的调用都会被转发到该类对象下。
        });
   }
}

Step 5 − 在config/app.php注册ServiceProvider类

Step 6 − 在config/app.php注册自定义Facade的别名

使用测试：

Add the following lines in app/Http/routes.php.

Route::get('/facadeex', function(){
   return TestFacades::testingFacades();
});

Step 9 − Visit the following URL to test the Facade.

http://localhost:8000/facadeex去查看输出