根据之前一篇文章，我们知道 Yii2 的事件分两类，一是类级别的事件，二是实例级别的事件。类级别的事件是基于 yii\base\Event 实现，实例级别的事件是基于 yii\base\Component 实现。 今天先来看下类级别事件的实现，代码是yii\base\Event 类。 ? phpnamespa
根据之前一篇文章，我们知道 Yii2 的事件分两类，一是类级别的事件，二是实例级别的事件。类级别的事件是基于 yii\base\Event 实现，实例级别的事件是基于 yii\base\Component 实现。
今天先来看下类级别事件的实现，代码是 yii\base\Event 类。
<span style="color: #000000;">php
namespace yii\base;
</span><span style="color: #008000;">/*</span><span style="color: #008000;">*
* Event is the base class for all event classes.
</span><span style="color: #008000;">*/</span>
<span style="color: #0000ff;">class</span> Event <span style="color: #0000ff;">extends</span> <span style="color: #0000ff;">Object</span><span style="color: #000000;">
{
</span><span style="color: #008000;">/*</span><span style="color: #008000;">*
* @var string the event name. This PRoperty is set by [[Component::trigger()]] and [[trigger()]].
* Event handlers may use this property to check what event it is handling.
* 事件的名字
</span><span style="color: #008000;">*/</span>
<span style="color: #0000ff;">public</span> <span style="color: #800080;">$name</span><span style="color: #000000;">;
</span><span style="color: #008000;">/*</span><span style="color: #008000;">*
* @var object the sender of this event. If not set, this property will be
* set as the object whose "trigger()" method is called.
* This property may also be a `null` when this event is a
* class-level event which is triggered in a static context.
* 触发事件的对象
</span><span style="color: #008000;">*/</span>
<span style="color: #0000ff;">public</span> <span style="color: #800080;">$sender</span><span style="color: #000000;">;
</span><span style="color: #008000;">/*</span><span style="color: #008000;">*
* @var boolean whether the event is handled. Defaults to false.
* When a handler sets this to be true, the event processing will stop and
* ignore the rest of the uninvoked event handlers.
* 记录事件是否已被处理，当 handled 被设置为 true 时，执行到这个 event 的时候，会停止，并忽略剩下的 event
</span><span style="color: #008000;">*/</span>
<span style="color: #0000ff;">public</span> <span style="color: #800080;">$handled</span> = <span style="color: #0000ff;">false</span><span style="color: #000000;">;
</span><span style="color: #008000;">/*</span><span style="color: #008000;">*
* @var mixed the data that is passed to [[Component::on()]] when attaching an event handler.
* Note that this varies according to which event handler is currently executing.
</span><span style="color: #008000;">*/</span>
<span style="color: #0000ff;">public</span> <span style="color: #800080;">$data</span><span style="color: #000000;">;
</span><span style="color: #008000;">/*</span><span style="color: #008000;">*
* 存储所有的 event，因为是 static 的属性，所有的 event 对象/类都共享这一份数据
</span><span style="color: #008000;">*/</span>
<span style="color: #0000ff;">private</span> <span style="color: #0000ff;">static</span> <span style="color: #800080;">$_events</span> =<span style="color: #000000;"> [];
</span><span style="color: #008000;">/*</span><span style="color: #008000;">*
* Attaches an event handler to a class-level event.
*
* When a class-level event is triggered, event handlers attached
* to that class and all parent classes will be invoked.
*
* For example, the following code attaches an event handler to `ActiveRecord`'s
* `afterInsert` event:
*
* ~~~
* Event::on(ActiveRecord::className(), ActiveRecord::EVENT_AFTER_INSERT, function ($event) {
* Yii::trace(get_class($event->sender) . ' is inserted.');
* });
* ~~~
*
* The handler will be invoked for EVERY successful ActiveRecord insertion.
*
* For more details about how to declare an event handler, please refer to [[Component::on()]].
*
* 为一个类添加事件
*
* @param string $class the fully qualified class name to which the event handler needs to attach.
* @param string $name the event name.
* @param callable $handler the event handler.
* @param mixed $data the data to be passed to the event handler when the event is triggered.
* When the event handler is invoked, this data can be accessed via [[Event::data]].
* @param boolean $append whether to append new event handler to the end of the existing
* handler list. If false, the new handler will be inserted at the beginning of the existing
* handler list.
* @see off()
</span><span style="color: #008000;">*/</span>
<span style="color: #0000ff;">public</span> <span style="color: #0000ff;">static</span> <span style="color: #0000ff;">function</span> on(<span style="color: #800080;">$class</span>, <span style="color: #800080;">$name</span>, <span style="color: #800080;">$handler</span>, <span style="color: #800080;">$data</span> = <span style="color: #0000ff;">null</span>, <span style="color: #800080;">$append</span> = <span style="color: #0000ff;">true</span><span style="color: #000000;">)
{
</span><span style="color: #008000;">//</span><span style="color: #008000;"> 去掉 class 最左边的斜杠</span>
<span style="color: #800080;">$class</span> = <span style="color: #008080;">ltrim</span>(<span style="color: #800080;">$class</span>, '\\'<span style="color: #000000;">);
</span><span style="color: #008000;">//</span><span style="color: #008000;"> 如果 append 为true，就放到 $_events 中名字为 $name 的数组的最后，否则放到最前面</span>
<span style="color: #0000ff;">if</span> (<span style="color: #800080;">$append</span> || <span style="color: #0000ff;">empty</span>(self::<span style="color: #800080;">$_events</span>[<span style="color: #800080;">$name</span>][<span style="color: #800080;">$class</span><span style="color: #000000;">])) {
self</span>::<span style="color: #800080;">$_events</span>[<span style="color: #800080;">$name</span>][<span style="color: #800080;">$class</span>][] = [<span style="color: #800080;">$handler</span>, <span style="color: #800080;">$data</span><span style="color: #000000;">];
} </span><span style="color: #0000ff;">else</span><span style="color: #000000;"> {
</span><span style="color: #008080;">array_unshift</span>(self::<span style="color: #800080;">$_events</span>[<span style="color: #800080;">$name</span>][<span style="color: #800080;">$class</span>], [<span style="color: #800080;">$handler</span>, <span style="color: #800080;">$data</span><span style="color: #000000;">]);
}
}
</span><span style="color: #008000;">/*</span><span style="color: #008000;">*
* Detaches an event handler from a class-level event.
*
* This method is the opposite of [[on()]].
*
* 移除一个类的事件
*
* @param string $class the fully qualified class name from which the event handler needs to be detached.
* @param string $name the event name.
* @param callable $handler the event handler to be removed.
* If it is null, all handlers attached to the named event will be removed.
* @return boolean whether a handler is found and detached.
* @see on()
</span><span style="color: #008000;">*/</span>
<span style="color: #0000ff;">public</span> <span style="color: #0000ff;">static</span> <span style="color: #0000ff;">function</span> off(<span style="color: #800080;">$class</span>, <span style="color: #800080;">$name</span>, <span style="color: #800080;">$handler</span> = <span style="color: #0000ff;">null</span><span style="color: #000000;">)
{
</span><span style="color: #800080;">$class</span> = <span style="color: #008080;">ltrim</span>(<span style="color: #800080;">$class</span>, '\\'<span style="color: #000000;">);
</span><span style="color: #0000ff;">if</span> (<span style="color: #0000ff;">empty</span>(self::<span style="color: #800080;">$_events</span>[<span style="color: #800080;">$name</span>][<span style="color: #800080;">$class</span><span style="color: #000000;">])) {
</span><span style="color: #008000;">//</span><span style="color: #008000;"> 不存在该事件</span>
<span style="color: #0000ff;">return</span> <span style="color: #0000ff;">false</span><span style="color: #000000;">;
}
</span><span style="color: #0000ff;">if</span> (<span style="color: #800080;">$handler</span> === <span style="color: #0000ff;">null</span><span style="color: #000000;">) {
</span><span style="color: #008000;">//</span><span style="color: #008000;"> 如果 handler 为空，直接将在该类下该事件移除，即移出所有的是这个名字的事件</span>
<span style="color: #0000ff;">unset</span>(self::<span style="color: #800080;">$_events</span>[<span style="color: #800080;">$name</span>][<span style="color: #800080;">$class</span><span style="color: #000000;">]);
</span><span style="color: #0000ff;">return</span> <span style="color: #0000ff;">true</span><span style="color: #000000;">;
} </span><span style="color: #0000ff;">else</span><span style="color: #000000;"> {
</span><span style="color: #800080;">$removed</span> = <span style="color: #0000ff;">false</span><span style="color: #000000;">;
</span><span style="color: #008000;">//</span><span style="color: #008000;"> 如果 $handler 不为空，循环 $_events 找到相应的 handler，只移除这个 handler 和 data 组成的数组</span>
<span style="color: #0000ff;">foreach</span> (self::<span style="color: #800080;">$_events</span>[<span style="color: #800080;">$name</span>][<span style="color: #800080;">$class</span>] <span style="color: #0000ff;">as</span> <span style="color: #800080;">$i</span> => <span style="color: #800080;">$event</span><span style="color: #000000;">) {
</span><span style="color: #0000ff;">if</span> (<span style="color: #800080;">$event</span>[0] === <span style="color: #800080;">$handler</span><span style="color: #000000;">) {
</span><span style="color: #0000ff;">unset</span>(self::<span style="color: #800080;">$_events</span>[<span style="color: #800080;">$name</span>][<span style="color: #800080;">$class</span>][<span style="color: #800080;">$i</span><span style="color: #000000;">]);
</span><span style="color: #800080;">$removed</span> = <span style="color: #0000ff;">true</span><span style="color: #000000;">;
}
}
</span><span style="color: #0000ff;">if</span> (<span style="color: #800080;">$removed</span><span style="color: #000000;">) {
</span><span style="color: #008000;">//</span><span style="color: #008000;"> 移除之后，使数组重新变成一个自然数组</span>
self::<span style="color: #800080;">$_events</span>[<span style="color: #800080;">$name</span>][<span style="color: #800080;">$class</span>] = <span style="color: #008080;">array_values</span>(self::<span style="color: #800080;">$_events</span>[<span style="color: #800080;">$name</span>][<span style="color: #800080;">$class</span><span style="color: #000000;">]);
}
</span><span style="color: #0000ff;">return</span> <span style="color: #800080;">$removed</span><span style="color: #000000;">;
}
}
</span><span style="color: #008000;">/*</span><span style="color: #008000;">*
* Returns a value indicating whether there is any handler attached to the specified class-level event.
* Note that this method will also check all parent classes to see if there is any handler attached
* to the named event.
* 检测在某个类或者对象是否具有某个事件
* @param string|object $class the object or the fully qualified class name specifying the class-level event.
* @param string $name the event name.
* @return boolean whether there is any handler attached to the event.
</span><span style="color: #008000;">*/</span>
<span style="color: #0000ff;">public</span> <span style="color: #0000ff;">static</span> <span style="color: #0000ff;">function</span> hasHandlers(<span style="color: #800080;">$class</span>, <span style="color: #800080;">$name</span><span style="color: #000000;">)
{
</span><span style="color: #0000ff;">if</span> (<span style="color: #0000ff;">empty</span>(self::<span style="color: #800080;">$_events</span>[<span style="color: #800080;">$name</span><span style="color: #000000;">])) {
</span><span style="color: #008000;">//</span><span style="color: #008000;"> 不存在，直接返回</span>
<span style="color: #0000ff;">return</span> <span style="color: #0000ff;">false</span><span style="color: #000000;">;
}
</span><span style="color: #0000ff;">if</span> (<span style="color: #008080;">is_object</span>(<span style="color: #800080;">$class</span><span style="color: #000000;">)) {
</span><span style="color: #008000;">//</span><span style="color: #008000;"> 如果是一个 object，就获取其类名</span>
<span style="color: #800080;">$class</span> = <span style="color: #008080;">get_class</span>(<span style="color: #800080;">$class</span><span style="color: #000000;">);
} </span><span style="color: #0000ff;">else</span><span style="color: #000000;"> {
</span><span style="color: #008000;">//</span><span style="color: #008000;"> 如果是一个类名，就去掉 class 最左边的斜杠</span>
<span style="color: #800080;">$class</span> = <span style="color: #008080;">ltrim</span>(<span style="color: #800080;">$class</span>, '\\'<span style="color: #000000;">);
}
</span><span style="color: #008000;">//</span><span style="color: #008000;"> 如果该类中找不到，就去父类中找，直到找到或者没有父类了为止</span>
<span style="color: #0000ff;">do</span><span style="color: #000000;"> {
</span><span style="color: #0000ff;">if</span> (!<span style="color: #0000ff;">empty</span>(self::<span style="color: #800080;">$_events</span>[<span style="color: #800080;">$name</span>][<span style="color: #800080;">$class</span><span style="color: #000000;">])) {
</span><span style="color: #0000ff;">return</span> <span style="color: #0000ff;">true</span><span style="color: #000000;">;
}
} </span><span style="color: #0000ff;">while</span> ((<span style="color: #800080;">$class</span> = <span style="color: #008080;">get_parent_class</span>(<span style="color: #800080;">$class</span>)) !== <span style="color: #0000ff;">false</span><span style="color: #000000;">);
</span><span style="color: #0000ff;">return</span> <span style="color: #0000ff;">false</span><span style="color: #000000;">;
}
</span><span style="color: #008000;">/*</span><span style="color: #008000;">*
* Triggers a class-level event.
* This method will cause invocation of event handlers that are attached to the named event
* for the specified class and all its parent classes.
* 触发某个类或者对象的某个事件
* @param string|object $class the object or the fully qualified class name specifying the class-level event.
* @param string $name the event name.
* @param Event $event the event parameter. If not set, a default [[Event]] object will be created.
</span><span style="color: #008000;">*/</span>
<span style="color: #0000ff;">public</span> <span style="color: #0000ff;">static</span> <span style="color: #0000ff;">function</span> trigger(<span style="color: #800080;">$class</span>, <span style="color: #800080;">$name</span>, <span style="color: #800080;">$event</span> = <span style="color: #0000ff;">null</span><span style="color: #000000;">)
{
</span><span style="color: #0000ff;">if</span> (<span style="color: #0000ff;">empty</span>(self::<span style="color: #800080;">$_events</span>[<span style="color: #800080;">$name</span><span style="color: #000000;">])) {
</span><span style="color: #0000ff;">return</span><span style="color: #000000;">;
}
</span><span style="color: #0000ff;">if</span> (<span style="color: #800080;">$event</span> === <span style="color: #0000ff;">null</span><span style="color: #000000;">) {
</span><span style="color: #008000;">//</span><span style="color: #008000;"> 事件不存在，就创建一个 Event 对象</span>
<span style="color: #800080;">$event</span> = <span style="color: #0000ff;">new</span> <span style="color: #0000ff;">static</span><span style="color: #000000;">;
}
</span><span style="color: #008000;">//</span><span style="color: #008000;"> 设置event对象的属性，默认是未被处理的</span>
<span style="color: #800080;">$event</span>->handled = <span style="color: #0000ff;">false</span><span style="color: #000000;">;
</span><span style="color: #800080;">$event</span>->name = <span style="color: #800080;">$name</span><span style="color: #000000;">;
</span><span style="color: #0000ff;">if</span> (<span style="color: #008080;">is_object</span>(<span style="color: #800080;">$class</span><span style="color: #000000;">)) {
</span><span style="color: #0000ff;">if</span> (<span style="color: #800080;">$event</span>->sender === <span style="color: #0000ff;">null</span><span style="color: #000000;">) {
</span><span style="color: #008000;">//</span><span style="color: #008000;"> 如果 $class 是个对象，并且是 sender 为空，就将 $class 赋给 sender，即 $class 就是触发事件的对象</span>
<span style="color: #800080;">$event</span>->sender = <span style="color: #800080;">$class</span><span style="color: #000000;">;
}
</span><span style="color: #800080;">$class</span> = <span style="color: #008080;">get_class</span>(<span style="color: #800080;">$class</span><span style="color: #000000;">);
} </span><span style="color: #0000ff;">else</span><span style="color: #000000;"> {
</span><span style="color: #800080;">$class</span> = <span style="color: #008080;">ltrim</span>(<span style="color: #800080;">$class</span>, '\\'<span style="color: #000000;">);
}
</span><span style="color: #008000;">//</span><span style="color: #008000;"> 循环类的 $_event，直到遇到 $event->handled 为真或者没有父类了为止</span>
<span style="color: #0000ff;">do</span><span style="color: #000000;"> {
</span><span style="color: #0000ff;">if</span> (!<span style="color: #0000ff;">empty</span>(self::<span style="color: #800080;">$_events</span>[<span style="color: #800080;">$name</span>][<span style="color: #800080;">$class</span><span style="color: #000000;">])) {
</span><span style="color: #0000ff;">foreach</span> (self::<span style="color: #800080;">$_events</span>[<span style="color: #800080;">$name</span>][<span style="color: #800080;">$class</span>] <span style="color: #0000ff;">as</span> <span style="color: #800080;">$handler</span><span style="color: #000000;">) {
</span><span style="color: #008000;">//</span><span style="color: #008000;"> 将参数赋到 event 对象的 data 属性上</span>
<span style="color: #800080;">$event</span>->data = <span style="color: #800080;">$handler</span>[1<span style="color: #000000;">];
</span><span style="color: #008000;">//</span><span style="color: #008000;"> 调用 $handler 方法
// 在方法中，可以用 $this->data 取到相应的参数
// 也可以在其中设置 $this->handled 的值，中断后续事件的触发</span>
<span style="color: #008080;">call_user_func</span>(<span style="color: #800080;">$handler</span>[0], <span style="color: #800080;">$event</span><span style="color: #000000;">);
</span><span style="color: #008000;">//</span><span style="color: #008000;"> 当某个 handled 被设置为 true 时，执行到这个事件的时候，会停止，并忽略剩下的事件</span>
<span style="color: #0000ff;">if</span> (<span style="color: #800080;">$event</span>-><span style="color: #000000;">handled) {
</span><span style="color: #0000ff;">return</span><span style="color: #000000;">;
}
}
}
} </span><span style="color: #0000ff;">while</span> ((<span style="color: #800080;">$class</span> = <span style="color: #008080;">get_parent_class</span>(<span style="color: #800080;">$class</span>)) !== <span style="color: #0000ff;">false</span><span style="color: #000000;">);
}
}</span>通过上面代码可以看出，类级别的 Event，其本质就是在 Event 类中的 $_events 变量中存储事件，触发事件的时候，只需将其取出，执行即可。
$_events里面的数据结构大概如下：
<span style="color: #000000;">[
</span>'add' =><span style="color: #000000;"> [
</span>'Child' =><span style="color: #000000;"> [
[</span><span style="color: #0000ff;">function</span> (<span style="color: #800080;">$event</span>) { ... }, <span style="color: #800080;">$data</span>],<span style="color: #000000;">
[[</span><span style="color: #800080;">$object</span>, 'handleAdd'], <span style="color: #0000ff;">null</span>],<span style="color: #000000;">
[[</span>'ChildClass', 'handleAdd'], <span style="color: #800080;">$data</span>],<span style="color: #000000;">
[</span>'handleAdd', <span style="color: #800080;">$data</span><span style="color: #000000;">]
]</span>,
'ChildClass' =><span style="color: #000000;"> [
</span>...<span style="color: #000000;">
]
]</span>,
'delete' =><span style="color: #000000;"> [
</span>...<span style="color: #000000;">
]
]</span>之后讲到yii\base\Component类时，我们会再来说一下实例级别的事件。
对 Yii2 源码有兴趣的同学可以关注项目 yii2-2.0.3-annotated，现在在上面已经添加了不少关于 Yii2 源码的注释，之后还会继续添加～
有兴趣的同学也可以参与进来，提交 Yii2 源码的注释。
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