yii2源码学习笔记(三）

组件（component），是Yii框架的基类，实现了属性、事件、行为三类功能，如果需要事件和行为的功能，需要继承该类。

yii\base\Component代码详解

 <?php
 /**
  * @link http://www.yiiframework.com/
  * @copyright Copyright (c) 2008 Yii Software LLC
  * @license http://www.yiiframework.com/license/
  */

 namespace yii\base;
 //命名空间
 use Yii;
 //加载Yii相关类
 /**
  * Component is the base class that implements the *property*, *event* and *behavior* features.
  * 组件是实现属性、事件、行为的基类
  * Component provides the *event* and *behavior* features, in addition to the *property* feature which is implemented in
  * its parent class [[Object]].
  * 组件提供事件和行为，继承他父类Object的特点
  * Event is a way to "inject" custom code into existing code at certain places. For example, a comment object can trigger
  * an "add" event when the user adds a comment. We can write custom code and attach it to this event so that when the event
  * is triggered (i.e. comment will be added), our custom code will be executed.
  *
  * An event is identified by a name that should be unique within the class it is defined at. Event names are *case-sensitive*.
  * 事件是一种在特定的地方“注入”自定义代码到现有的代码。例如，
  * 当一个用户添加评论事件时，注释的对象可以触发。我们可以编写自定义代码，并将其附加到此事件，这样当事件被触发（即评论将被添加），
  *
  * 我们的自定义代码会被执行，
  * One or multiple PHP callbacks, called *event handlers*, can be attached to an event. You can call [[trigger()]] to
  * raise an event. When an event is raised, the event handlers will be invoked automatically in the order they were
  * attached.
  *
  * To attach an event handler to an event, call [[on()]]:
  * 一个或多个php回调，称为为‘事件处理’。要触发一个事件处理，可以用on();举个例子。
  * ~~~
  * $post->on('update', function ($event) {
  *     // send email notification
  * });
  * ~~~
  *
  * In the above, an anonymous function is attached to the "update" event of the post. You may attach
  * the following types of event handlers:
  *  一个匿名函数被连接到'update'事件后。可以用以下类型的程序做处理：
  * - anonymous function: `function ($event) { ... }`    匿名函数
  * - object method: `[$object, 'handleAdd']`            对象方法
  * - static class method: `['Page', 'handleAdd']`       静态类方法
  * - global function: `'handleAdd'`                     全局函数
  *
  * The signature of an event handler should be like the following:
  * 一个事件处理程序的签名应该是如下：
  * ~~~
  * function foo($event)
  * ~~~
  *
  * where `$event` is an [[Event]] object which includes parameters associated with the event.
  * $event是一个[[Event]]对象 包括与事件相关联的参数。
  * You can also attach a handler to an event when configuring a component with a configuration array.
  * The syntax is like the following:
  * 还可以将处理程序附加到配置数组中配置组件的事件。语法如下：
  * ~~~
  * [
  *     'on add' => function ($event) { ... }
  * ]
  * ~~~
  *
  * where `on add` stands for attaching an event to the `add` event.
  * `on add` 代表添加事件
  * Sometimes, you may want to associate extra data with an event handler when you attach it to an event
  * and then access it when the handler is invoked. You may do so by
  * 有时，当你将它附加到一个事件时，你可能会把额外的数据与事件处理程序关联起来
  * 然后在调用处理程序时访问它。
  * ~~~
  * $post->on('update', function ($event) {
  *     // the data can be accessed via $event->data
  * }, $data);
  * ~~~
  *
  * A behavior is an instance of [[Behavior]] or its child class. A component can be attached with one or multiple
  * behaviors. When a behavior is attached to a component, its public properties and methods can be accessed via the
  * component directly, as if the component owns those properties and methods.
  * 行为是行为的一个实例或它的子类。一个组件可以连接一个或多个
  * 行为。当一个行为被连接到一个组件，它的公共属性和方法可以通过访问
  * 组件的直接组件，因为组件拥有这些属性和方法。
  * To attach a behavior to a component, declare it in [[behaviors()]], or explicitly call [[attachBehavior]]. Behaviors
  * declared in [[behaviors()]] are automatically attached to the corresponding component.
  *
  * One can also attach a behavior to a component when configuring it with a configuration array. The syntax is like the
  * following:
  *
  * ~~~
  * [
  *     'as tree' => [
  *         'class' => 'Tree',
  *     ],
  * ]
  * ~~~
  *
  * where `as tree` stands for attaching a behavior named `tree`, and the array will be passed to [[\Yii::createObject()]]
  * to create the behavior object.
  *
  * @property Behavior[] $behaviors List of behaviors attached to this component. This property is read-only.
  *
  * @author Qiang Xue <qiang.xue@gmail.com>
  * @since 2.0
  */
 //该类继承了Object类
 class Component extends Object
 {
     /**
      * @var array the attached event handlers (event name => handlers)
      * 存储对象的事件处理程序，是一个数组
      */
     private $_events = [];
     /**
      * @var Behavior[]|null the attached behaviors (behavior name => behavior). This is `null` when not initialized.
      * 赋值给对象的行为，默认值为null
      */
     private $_behaviors;

     /**
      * Returns the value of a component property.
      * 得到属性值
      * This method will check in the following order and act accordingly:
      *
      *  - a property defined by a getter: return the getter result
      *  - a property of a behavior: return the behavior property value
      *
      * Do not call this method directly as it is a PHP magic method that
      * 重写 Object 中的 getter 方法
      * 返回一个组件的属性值。
      * 这个方法将检查以下顺序并采取相应的行动：
      *
      * - 通过一个getter定义的属性：返回getter的结果
      * - 一个行为的属性：返回的行为属性值
      *
      * 不要直接调用此方法，因为它是一个PHP魔术方法
      * will be implicitly called when executing `$value = $component->property;`.
      * @param string $name the property name    参数属性名
      * @return mixed the property value or the value of a behavior's property 返回混合属性的值或行为属性的值
      * @throws UnknownPropertyException if the property is not defined  如果没有定义，抛出信息
      * @throws InvalidCallException if the property is write-only.  该属性是只写的
      * @see __set()
      */
     public function __get($name)
     {
         $getter = 'get' . $name;    //定义$getter
         if (method_exists($this, $getter)) {
             // read property, e.g. getName()
             //方法存在且被调用时，读取属性
             return $this->$getter();
         } else {
             // behavior property
             $this->ensureBehaviors(); //确保行为已经绑定
             foreach ($this->_behaviors as $behavior) {
                 if ($behavior->canGetProperty($name)) {
                     /**
                      * 判断检查对象或类是否能够获取 $name 属性，
                      * 如果 behavior 中含有该属性，就返回 behavior 中的这个属性
                      * 第二个参数为 true（默认是true），则不局限于是否有 getter
                      */
                     return $behavior->$name;
                 }
             }
         }
         if (method_exists($this, 'set' . $name)) {//方法存在且调用，返回true
             throw new InvalidCallException('Getting write-only property: ' . get_class($this) . '::' . $name);
             //抛出只读属性
         } else {
             throw new UnknownPropertyException('Getting unknown property: ' . get_class($this) . '::' . $name);
             //错误扔出异常
         }
     }

     /**
      * Sets the value of a component property.  设置属性值
      * This method will check in the following order and act accordingly:检查并执行
      *
      *  - a property defined by a setter: set the property value
      *  - an event in the format of "on xyz": attach the handler to the event "xyz"
      *  - a behavior in the format of "as xyz": attach the behavior named as "xyz"
      *  - a property of a behavior: set the behavior property value
      * 重写 Object 中的 setter 方法
      * 由一个setter定义的属性:设置属性值。
      * 如果 $name 是 'on xyz'，就会将 xyz 事件添加到该对象中
      * 如果 $name 是 'as xyz'，就会将 xyz 行为添加到该对象中
      * 添加对 behaviors 的处理，循环 behaviors，如果其中有相应的属性，就设置它
      * Do not call this method directly as it is a PHP magic method that
      * will be implicitly called when executing `$component->property = $value;`.
      * @param string $name the property name or the event name 属性名或者事件名
      * @param mixed $value the property value       属性值
      * @throws UnknownPropertyException if the property is not defined  未定义扔出错误
      * @throws InvalidCallException if the property is read-only.   抛出信息 只读
      * @see __get()
      */
     public function __set($name, $value)
     {
         $setter = 'set' . $name;//在属性名前面加set构建setter方法
         if (method_exists($this, $setter)) {
             // set property
             //如果setter方法存在返回true,没有返回false.    调用该方法设置属性值
             $this->$setter($value);

             return;
         } elseif (strncmp($name, 'on ', 3) === 0) {//比较$name和'on '前3个字符，如果$name以on+空格开始，就添加事件
             // on event: attach event handler
             $this->on(trim(substr($name, 3)), $value);//执行on 方法，用来添加附加事件。

             return;
         } elseif (strncmp($name, 'as ', 3) === 0) {//如果$name以as+空格开始，就添加行为
             // as behavior: attach behavior
             $name = trim(substr($name, 3));//截取as后面的字符，用attachBehavior来添加附加行为。
             //$value这个对象是Behavior类的一个实例，取$value为参数，否则静态调用Yii方法创造一个新的对象。
             $this->attachBehavior($name, $value instanceof Behavior ? $value : Yii::createObject($value));

             return;
         } else {
             // behavior property
             $this->ensureBehaviors();//确保行为已经绑定
             foreach ($this->_behaviors as $behavior) {
                 if ($behavior->canSetProperty($name)) {//遍历行为，如果行为中有可以设置的属性$name
                     $behavior->$name = $value;//给该行为类中的属性设置属性值    

                     return;
                 }
             }
         }
         if (method_exists($this, 'get' . $name)) {//如果'get'.$name这个方法存在，就抛出只读信息.
             throw new InvalidCallException('Setting read-only property: ' . get_class($this) . '::' . $name);
         } else {
             //如果不属于这个类，就抛出异常.
             throw new UnknownPropertyException('Setting unknown property: ' . get_class($this) . '::' . $name);
         }
     }

     /**
      * Checks if a property value is null.
      * 属性是否为空
      * This method will check in the following order and act accordingly:
      *
      *  - a property defined by a setter: return whether the property value is null
      *  - a property of a behavior: return whether the property value is null
      *  重写 Object 中的 isset 方法 通过一个setter定义的属性：返回属性是否设置
      * 行为的属性:返回属性值是否设置
      * Do not call this method directly as it is a PHP magic method that
      * will be implicitly called when executing `isset($component->property)`.
      * @param string $name the property name or the event name  属性名或事件名
      * @return boolean whether the named property is null   　属性值是否被设置 返回true/boolean值。
      */
     public function __isset($name)
     {
         $getter = 'get' . $name;
         if (method_exists($this, $getter)) {
              // 判断是否有getter方法，有 getter 方法且获取的值不为 null，才认为该属性存在
             return $this->$getter() !== null;
         } else {
             // behavior property
             $this->ensureBehaviors();//确定行为已经绑定
             foreach ($this->_behaviors as $behavior) {//遍历行为
                 if ($behavior->canGetProperty($name)) {
                     // 如果 behavior 中有 $name 属性，且不为 null，该属性存在 返回 true
                     return $behavior->$name !== null;
                 }
             }
         }
         return false;
     }

     /**
      * Sets a component property to be null.
      * 设置属性为null，即删除属性
      * This method will check in the following order and act accordingly:
      *
      *  - a property defined by a setter: set the property value to be null
      *  - a property of a behavior: set the property value to be null
      * 重写 Object 中的 unset 方法，
      * 通过setter定义的属性：设置该属性值为空
      * 属性的行为：将属性值设为空
      * Do not call this method directly as it is a PHP magic method that
      * will be implicitly called when executing `unset($component->property)`.
      * @param string $name the property name    属性名
      * @throws InvalidCallException if the property is read only.   该属性只读，抛出异常
      */
     public function __unset($name)
     {
         $setter = 'set' . $name;
         if (method_exists($this, $setter)) {
             //如果$setter方法存在，通过setter方法把它设置为空
             $this->$setter(null);
             return;
         } else {
             // behavior property
             $this->ensureBehaviors();
             foreach ($this->_behaviors as $behavior) {//遍历行为
                 if ($behavior->canSetProperty($name)) {//存在$name值，设为空
                     $behavior->$name = null;
                     return;
                 }
             }
         }
         //抛出异常
         throw new InvalidCallException('Unsetting an unknown or read-only property: ' . get_class($this) . '::' . $name);
     }

     /**
      * Calls the named method which is not a class method.
      *
      * This method will check if any attached behavior has
      * the named method and will execute it if available.
      * 调用方法名 重写 Object 中的 call 方法，添加对行为的处理，循环 behaviors，
      * 如果其中有相应方法，就执行该 behavior 的方法
      * Do not call this method directly as it is a PHP magic method that
      * will be implicitly called when an unknown method is being invoked.
      * @param string $name the method name
      * @param array $params method parameters
      * @return mixed the method return value
      * @throws UnknownMethodException when calling unknown method
      */
     public function __call($name, $params)
     {
         $this->ensureBehaviors();
         foreach ($this->_behaviors as $object) {
             if ($object->hasMethod($name)) {
                 //行为中存在名为 $name 的方法，就执行它
                 //call_user_func_array 调用回调函数，并把一个数组参数作为回调函数的参数
                 return call_user_func_array([$object, $name], $params);
             }
         }
         //抛出异常
         throw new UnknownMethodException('Calling unknown method: ' . get_class($this) . "::$name()");
     }

     /**
      * This method is called after the object is created by cloning an existing one.
      * It removes all behaviors because they are attached to the old object.
      * 通过克隆现有创建的对象后，此方法会被调用。
 　　 * 他将会消除所有的行为。所有的引用属性 仍然会是一个指向原来的变量的引用
      */
     public function __clone()
     {
         // 对象复制时，将它的 _events 设置为空数组，将 _behaviors 设置为 null
         $this->_events = [];
         $this->_behaviors = null;
     }

未完待续