laravel Facade理解

参考
https://sergeyzhuk.me/2016/05...

Facade

 Laravel facades serve as "static proxies" to underlying classes in the service container, providing the benefit of a terse, expressive syntax while maintaining more testability and flexibility than traditional static methods.

Laravel 门面为 Laravel 服务的使用提供了便捷方式 ,不再需要从服务容器中类型提示和契约解析即可直接通过静态门面调用.

可以理解为操作复杂对象的简化方法,就是外观模式里的外观类的方法.

对应设计模式里的外观模式，对类实例的方法的封装，使用起来更方便.

下面三种方法对某个实例方法来讲没有区别:

//facade
SomeService::someMethod();
// and
app()->make('some.service')->someMethod();
// or
App::make('some.service')->someMethod();

核心是php的魔术方法__callStacic,所有调用Facade里静态方法，都会进入这个函数，进行真正的(代理)调用.

    //Facde接口
    public static function __callStatic($method, $args)
    {
        $instance = static::getFacadeRoot();

        if (! $instance) {
            throw new RuntimeException('A facade root has not been set.');
        }

        return $instance->$method(...$args);
    }
    public static function getFacadeRoot()
    {
        return static::resolveFacadeInstance(static::getFacadeAccessor());
    }
    protected static function resolveFacadeInstance($name)
    {
        if (is_object($name)) {
            return $name;
        }

        if (isset(static::$resolvedInstance[$name])) {
            return static::$resolvedInstance[$name];
        }

        //核心就在这,$app就是上面的ioc容器实例
        if (static::$app) {
            return static::$resolvedInstance[$name] = static::$app[$name];
        }

        //真正的实例来源
        public static function swap($instance)
        {
            static::$resolvedInstance[static::getFacadeAccessor()] = $instance;

            if (isset(static::$app)) {
                //注册到Ioc容器
                static::$app->instance(static::getFacadeAccessor(), $instance);
            }
        }
    }

实现Facade接口的类，要实现getFacadeAccessor和resolveFacadeInstance,关联要真正的实例.

Date为例子,其真正的实例是DateFactory.

class Date extends Facade
{
    const DEFAULT_FACADE = DateFactory::class;

    /**
     * Get the registered name of the component.
     *
     * @return string
     *
     * @throws \RuntimeException
     */
    protected static function getFacadeAccessor()
    {
        return 'date';
    }

    /**
     * Resolve the facade root instance from the container.
     *
     * @param  string  $name
     * @return mixed
     */
    protected static function resolveFacadeInstance($name)
    {
        if (! isset(static::$resolvedInstance[$name]) && ! isset(static::$app, static::$app[$name])) {
            $class = static::DEFAULT_FACADE;
            //swap执行真正的instance绑定到ioc容器
            static::swap(new $class);
        }

        return parent::resolveFacadeInstance($name);
    }
}

想用Date时，可以:

//直接用门面静态方法
 \Illuminate\Support\Facades\Date::createXXX()

但Laravel 的门面作为服务容器中底层类的「静态代理」，相比于传统静态方法，在维护时能够提供更加易于测试、更加灵活、简明优雅的语法。

如果还是嫌弃用之前use xxxx\Facades\xx太麻烦，config.app里配置个alias:

?php
return [
    //...
    '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,
    ],

    // ...
];

直接用就好了:

Cache::get(...);