In-depth learning of Yii2--yiibaseEvent class

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>php
namespace yii\base;

</span><span>/*</span><span>*
 * Event is the base class for all event classes.
 </span><span>*/</span><span>class</span> Event <span>extends</span><span>Object</span><span>{
    </span><span>/*</span><span>*
     * @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>*/</span><span>public</span><span>$name</span><span>;
    </span><span>/*</span><span>*
     * @var object the sender of this event. If not set, this property will be
     * set as the object whose "trigger()" method is called.
     * This property may also be a `null` when this event is a
     * class-level event which is triggered in a static context.
     * 触发事件的对象
     </span><span>*/</span><span>public</span><span>$sender</span><span>;
    </span><span>/*</span><span>*
     * @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>*/</span><span>public</span><span>$handled</span> = <span>false</span><span>;
    </span><span>/*</span><span>*
     * @var mixed the data that is passed to [[Component::on()]] when attaching an event handler.
     * Note that this varies according to which event handler is currently executing.
     </span><span>*/</span><span>public</span><span>$data</span><span>;

    </span><span>/*</span><span>*
     * 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>*/</span><span>private</span><span>static</span><span>$_events</span> =<span> [];


    </span><span>/*</span><span>*
     * 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 $append whether to append new event handler to the end of the existing
     * handler list. If false, the new handler will be inserted at the beginning of the existing
     * handler list.
     * @see off()
     </span><span>*/</span><span>public</span><span>static</span><span>function</span> on(<span>$class</span>, <span>$name</span>, <span>$handler</span>, <span>$data</span> = <span>null</span>, <span>$append</span> = <span>true</span><span>)
    {
        </span><span>//</span><span> 去掉 class 最左边的斜杠</span><span>$class</span> = <span>ltrim</span>(<span>$class</span>, '\\'<span>);
        </span><span>//</span><span> 如果 append 为true，就放到 $_events 中名字为 $name 的数组的最后，否则放到最前面</span><span>if</span> (<span>$append</span> || <span>empty</span>(self::<span>$_events</span>[<span>$name</span>][<span>$class</span><span>])) {
            self</span>::<span>$_events</span>[<span>$name</span>][<span>$class</span>][] = [<span>$handler</span>, <span>$data</span><span>];
        } </span><span>else</span><span> {
            </span><span>array_unshift</span>(self::<span>$_events</span>[<span>$name</span>][<span>$class</span>], [<span>$handler</span>, <span>$data</span><span>]);
        }
    }

    </span><span>/*</span><span>*
     * 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 $handler the event handler to be removed.
     * If it is null, all handlers attached to the named event will be removed.
     * @return boolean whether a handler is found and detached.
     * @see on()
     </span><span>*/</span><span>public</span><span>static</span><span>function</span> off(<span>$class</span>, <span>$name</span>, <span>$handler</span> = <span>null</span><span>)
    {
        </span><span>$class</span> = <span>ltrim</span>(<span>$class</span>, '\\'<span>);
        </span><span>if</span> (<span>empty</span>(self::<span>$_events</span>[<span>$name</span>][<span>$class</span><span>])) {
            </span><span>//</span><span> 不存在该事件</span><span>return</span><span>false</span><span>;
        }
        </span><span>if</span> (<span>$handler</span> === <span>null</span><span>) {
            </span><span>//</span><span> 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>unset</span>(self::<span>$_events</span>[<span>$name</span>][<span>$class</span><span>]);
            </span><span>return</span><span>true</span><span>;
        } </span><span>else</span><span> {
            </span><span>$removed</span> = <span>false</span><span>;
            </span><span>//</span><span> 如果 $handler 不为空，循环 $_events 找到相应的 handler，只移除这个 handler 和 data 组成的数组</span><span>foreach</span> (self::<span>$_events</span>[<span>$name</span>][<span>$class</span>] <span>as</span><span>$i</span> => <span>$event</span><span>) {
                </span><span>if</span> (<span>$event</span>[0] === <span>$handler</span><span>) {
                    </span><span>unset</span>(self::<span>$_events</span>[<span>$name</span>][<span>$class</span>][<span>$i</span><span>]);
                    </span><span>$removed</span> = <span>true</span><span>;
                }
            }
            </span><span>if</span> (<span>$removed</span><span>) {
                </span><span>//</span><span> 移除之后，使数组重新变成一个自然数组</span>                self::<span>$_events</span>[<span>$name</span>][<span>$class</span>] = <span>array_values</span>(self::<span>$_events</span>[<span>$name</span>][<span>$class</span><span>]);
            }

            </span><span>return</span><span>$removed</span><span>;
        }
    }

    </span><span>/*</span><span>*
     * 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 $name the event name.
     * @return boolean whether there is any handler attached to the event.
     </span><span>*/</span><span>public</span><span>static</span><span>function</span> hasHandlers(<span>$class</span>, <span>$name</span><span>)
    {
        </span><span>if</span> (<span>empty</span>(self::<span>$_events</span>[<span>$name</span><span>])) {
            </span><span>//</span><span> 不存在，直接返回</span><span>return</span><span>false</span><span>;
        }
        </span><span>if</span> (<span>is_object</span>(<span>$class</span><span>)) {
            </span><span>//</span><span> 如果是一个 object，就获取其类名</span><span>$class</span> = <span>get_class</span>(<span>$class</span><span>);
        } </span><span>else</span><span> {
            </span><span>//</span><span> 如果是一个类名，就去掉 class 最左边的斜杠</span><span>$class</span> = <span>ltrim</span>(<span>$class</span>, '\\'<span>);
        }
        </span><span>//</span><span> 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>do</span><span> {
            </span><span>if</span> (!<span>empty</span>(self::<span>$_events</span>[<span>$name</span>][<span>$class</span><span>])) {
                </span><span>return</span><span>true</span><span>;
            }
        } </span><span>while</span> ((<span>$class</span> = <span>get_parent_class</span>(<span>$class</span>)) !== <span>false</span><span>);

        </span><span>return</span><span>false</span><span>;
    }

    </span><span>/*</span><span>*
     * 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 $event the event parameter. If not set, a default [[Event]] object will be created.
     </span><span>*/</span><span>public</span><span>static</span><span>function</span> trigger(<span>$class</span>, <span>$name</span>, <span>$event</span> = <span>null</span><span>)
    {
        </span><span>if</span> (<span>empty</span>(self::<span>$_events</span>[<span>$name</span><span>])) {
            </span><span>return</span><span>;
        }
        </span><span>if</span> (<span>$event</span> === <span>null</span><span>) {
            </span><span>//</span><span> 事件不存在，就创建一个 Event 对象</span><span>$event</span> = <span>new</span><span>static</span><span>;
        }
        </span><span>//</span><span> 设置event对象的属性，默认是未被处理的</span><span>$event</span>->handled = <span>false</span><span>;
        </span><span>$event</span>->name = <span>$name</span><span>;

        </span><span>if</span> (<span>is_object</span>(<span>$class</span><span>)) {
            </span><span>if</span> (<span>$event</span>->sender === <span>null</span><span>) {
                </span><span>//</span><span> 如果 $class 是个对象，并且是 sender 为空，就将 $class 赋给 sender，即 $class 就是触发事件的对象</span><span>$event</span>->sender = <span>$class</span><span>;
            }
            </span><span>$class</span> = <span>get_class</span>(<span>$class</span><span>);
        } </span><span>else</span><span> {
            </span><span>$class</span> = <span>ltrim</span>(<span>$class</span>, '\\'<span>);
        }
        </span><span>//</span><span> 循环类的 $_event，直到遇到 $event->handled 为真或者没有父类了为止</span><span>do</span><span> {
            </span><span>if</span> (!<span>empty</span>(self::<span>$_events</span>[<span>$name</span>][<span>$class</span><span>])) {
                </span><span>foreach</span> (self::<span>$_events</span>[<span>$name</span>][<span>$class</span>] <span>as</span><span>$handler</span><span>) {
                    </span><span>//</span><span> 将参数赋到 event 对象的 data 属性上</span><span>$event</span>->data = <span>$handler</span>[1<span>];
                    </span><span>//</span><span> 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 $this->handled 的值，中断后续事件的触发</span><span>call_user_func</span>(<span>$handler</span>[0], <span>$event</span><span>);
                    </span><span>//</span><span> 当某个 handled 被设置为 true 时，执行到这个事件的时候，会停止，并忽略剩下的事件</span><span>if</span> (<span>$event</span>-><span>handled) {
                        </span><span>return</span><span>;
                    }
                }
            }
        } </span><span>while</span> ((<span>$class</span> = <span>get_parent_class</span>(<span>$class</span>)) !== <span>false</span><span>);
    }
}</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>[
    </span>'add' =><span> [
        </span>'Child' =><span> [
            [</span><span>function</span> (<span>$event</span>) { ... }, <span>$data</span>],<span>            [[</span><span>$object</span>, 'handleAdd'], <span>null</span>],<span>            [[</span>'ChildClass', 'handleAdd'], <span>$data</span>],<span>            [</span>'handleAdd', <span>$data</span><span>]
        ]</span>,
        'ChildClass' =><span> [
            </span>...<span>        ]
    ]</span>,
    'delete' =><span> [
        </span>...<span>    ]
]</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。

 

以上就介绍了Yii2的深入学习--yii\base\Event 类，包括了方面的内容，希望对PHP教程有兴趣的朋友有所帮助。