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。

yiiaseComponent代码详解

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

namespace yiiase;
//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