这篇文章主要介绍Laravel中Contracts和Facades有什么用，文中介绍的非常详细，具有一定的参考价值，感兴趣的小伙伴们一定要看完！
Contracts
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.
/**
* 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.
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