11. 事件机制

[xiaohuilam]

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);