11. 事件机制

[Bruce Lam]

根据 Laravel 的 Events 文档 (中文版：事件系统)， EventServiceProvider 的使用方法为：

/**
 * 注册应用中的其它事件。
 *
 * @return void
 */
public function boot()
{
    parent::boot();

    Event::listen('event.name', function ($foo, $bar) {
        //
    });
}

如果花点时间研究 Event 这个 Facade，我们可以找到他穿透类其实为 Illuminate\Events\Dispatcher。

Illuminate\Events\Dispatcher 类的 __construct 方法为：

laravel/vendor/laravel/framework/src/Illuminate/Events/Dispatcher.php

Lines 59 to 62 in d081c91

 public function __construct(ContainerContract $container = null) 
 { 
     $this->container = $container ?: new Container; 
 } 

作用是将容器设置到 $this->container 属性

监听

我们刚刚在 EventServiceProvider 调用的 Event::listen 方法的代码为：

laravel/vendor/laravel/framework/src/Illuminate/Events/Dispatcher.php

Lines 71 to 80 in d081c91

 public function listen($events, $listener) 
 { 
     foreach ((array) $events as $event) { 
         if (Str::contains($event, '*')) { 
             $this->setupWildcardListen($event, $listener); 
         } else { 
             $this->listeners[$event][] = $this->makeListener($listener); 
         } 
     } 
 } 

如果监听了通配事件，setupWildcardListen 在辗转后跟 else 一样的调用到了 makeListener

laravel/vendor/laravel/framework/src/Illuminate/Events/Dispatcher.php

Lines 349 to 362 in d081c91

 public function makeListener($listener, $wildcard = false) 
 { 
     if (is_string($listener)) { 
         return $this->createClassListener($listener, $wildcard); 
     } 
  
     return function ($event, $payload) use ($listener, $wildcard) { 
         if ($wildcard) { 
             return $listener($event, $payload); 
         } 
  
         return $listener(...array_values($payload)); 
     }; 
 } 

注意，返回的是闭包！并不会立即执行。

在存放到 $this->listeners 后，事件们就静静地等待被触发

laravel/vendor/laravel/framework/src/Illuminate/Events/Dispatcher.php

Line 77 in d081c91

 $this->listeners[$event][] = $this->makeListener($listener); 

触发

在我们调用 event() 辅助方法后，触发的逻辑其实走到了 dispatch 方法

laravel/vendor/laravel/framework/src/Illuminate/Events/Dispatcher.php

Lines 193 to 229 in d081c91

 public function dispatch($event, $payload = [], $halt = false) 
 { 
     // When the given "event" is actually an object we will assume it is an event 
     // object and use the class as the event name and this event itself as the 
     // payload to the handler, which makes object based events quite simple. 
     list($event, $payload) = $this->parseEventAndPayload( 
         $event, $payload 
     ); 
  
     if ($this->shouldBroadcast($payload)) { 
         $this->broadcastEvent($payload[0]); 
     } 
  
     $responses = []; 
  
     foreach ($this->getListeners($event) as $listener) { 
         $response = $listener($event, $payload); 
  
         // If a response is returned from the listener and event halting is enabled 
         // we will just return this response, and not call the rest of the event 
         // listeners. Otherwise we will add the response on the response list. 
         if ($halt && ! is_null($response)) { 
             return $response; 
         } 
  
         // If a boolean false is returned from a listener, we will stop propagating 
         // the event to any further listeners down in the chain, else we keep on 
         // looping through the listeners and firing every one in our sequence. 
         if ($response === false) { 
             break; 
         } 
  
         $responses[] = $response; 
     } 
  
     return $halt ? null : $responses; 
 } 

核心逻辑就这句：

laravel/vendor/laravel/framework/src/Illuminate/Events/Dispatcher.php

Line 209 in d081c91

 $response = $listener($event, $payload);