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，不需要可直接继承Object类；
namespace yii\base;
use Yii;
/**
* Component is the base class that implements the *property*, *event* and *behavior* features.
* 组件，是Yii框架的基类，实现了属性、事件、行为三类功能
* Component provides the *event* and *behavior* features, in addition to the *property* feature which is implemented in
* its parent class [[Object]].
* 组件提供了事件和行为功能，通过附加到父类[[Object]]的属性功能中
* 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.
* 事件，可以在特定的时点，触发执行预先设定的一段代码，例如一个评论对象能够在用户添加评论的时候触发一个add事件，我们能够自定义一些代码添加到
* 这个事件中，在添加评论的时候会触发事件，执行自定义的代码
* An event is identified by a name that should be unique within the class it is defined at. Event names are *case-sensitive*.
* 事件的名称在类中是唯一的，区分大小写
* 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.
* 一个或者多个事件处理程序嫩巩固被添加到一个事件，能够通过调用[[trigger()]]触发事件，事件处理程序将会按照添加的先后顺序依次执行
* To attach an event handler to an event, call [[on()]]:
* 添加事件是通过on()方法添加
* ```php
* $post->on('update', function ($event) { //给update方法添加一个匿名函数的时间，该事件的作用是发送邮件信息
* // 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:
* 事件处理程序有以下几种形式
* - anonymous function: `function ($event) { ... }`匿名函数
* - object method: `[$object, 'handleAdd']` 对象的方法 以数组的方式传入
* - static class method: `['Page', 'handleAdd']` 静态方法 以数组的方式传入
* - global function: `'handleAdd'` 全局函数 不带参数和括号，只有函数名
*
* The signature of an event handler should be like the following:
*
* ```php
* function foo($event) 事件处理程序的格式
* ```
*
* where `$event` is an [[Event]] object which includes parameters associated with the event.
*
* You can also attach a handler to an event when configuring a component with a configuration array.
* The syntax is like the following:
* 可以通过配置文件来配置事件，格式如下
* ```php
* [
* 'on add' => function ($event) { ... } 给add 添加一个事件
* ]
* ```
*
* where `on add` stands for attaching an event to the `add` event.
*
* 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
* on()方法的第三个参数可以给事件处理程序传入参数
* ```php
* $post->on('update', function ($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.
* 行为可以在不修改现有类的情况下，对类的功能进行扩充。 通过将行为绑定到一个类，可以使类具有行为本身所定义的属性和方法，
* 就好像类本来就有这些属性和方法一样。 而且不需要写一个新的类去继承或包含现有类。
* 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:
* 配置行为的数组格式
* ```php
* [
* '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
*/
class Component extends Object
{
/**
* @var array 当前对象的已绑定的事件数组 (事件名 => 处理程序)
*/
private $_events = [];
/**
* @var Behavior[]|null 当前对象的已绑定的行为数组 (行为名 => 行为类). 初始化之前为空.
*/
private $_behaviors;
/**
* Returns the value of a component property.
* This method will check in the following order and act accordingly:
*
* - a property defined by a getter: return the getter result
* - a property of a behavior: return the behavior property value
*
* 重写 Object 中的 getter 方法，添加对 behaviors 的处理
* 如果当前组件的属性中没有该属性，则遍历 behaviors，如果其中有相应的属性，返回behaviors中的属性
*
* Do not call this method directly as it is a PHP magic method that
* will be implicitly called when executing `$value = $component->property;`.
* @param string $name 属性名
* @return mixed 属性值或者行为中的属性值
* @throws 属性未定义
* @throws 属性只读
* @see __set()
*/
public function __get($name)
{
$getter = 'get' . $name;
if (method_exists($this, $getter)) {
// 构造getter方法，如果getter方法存在的话，调用getter方法，返回属性值
return $this->$getter();
} else {
// behavior property
$this->ensureBehaviors();//调用该方法确保行为已绑定
foreach ($this->_behaviors as $behavior) {
if ($behavior->canGetProperty($name)) {
//调用父类的方法，判断检查对象或类是否能够获取 $name 属性，如果第二个参数为 true（默认是true），则不局限于是否有 getter
// 如果 behavior 中含有该属性，就返回 behavior 中的这个属性
return $behavior->$name;
}
}
}
if (method_exists($this, 'set' . $name)) {//跟父类相同，判断属性是否只写
throw new InvalidCallException('Getting write-only property: ' . get_class($this) . '::' . $name);
} else {//抛出异常
throw new UnknownPropertyException('Getting unknown property: ' . get_class($this) . '::' . $name);
}
}
/**
* Sets the value of a component property.
* This method will check in the following order and act accordingly:
*
* - 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
* 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 属性名或者事件名
* @param mixed $value the 属性值
* @throws UnknownPropertyException if the property is not defined
* @throws InvalidCallException if the property is read-only.
* @see __get()
*/
public function __set($name, $value)
{
$setter = 'set' . $name;//在属性名前面加set构建setter方法
if (method_exists($this, $setter)) {//如果setter方法存在
// 调用该方法设置属性值
$this->$setter($value);
return;
} elseif (strncmp($name, 'on ', 3) === 0) {//如果方法不存在，且$name以on+空格开始
// on event: attach event handler
$this->on(trim(substr($name, 3)), $value);//调用on方法将事件处理程序附加到事件
return;
} elseif (strncmp($name, 'as ', 3) === 0) {//否则，如果$name以as+空格开始
// as behavior: attach behavior
$name = trim(substr($name, 3));//截取as后面的字符
$this->attachBehavior($name, $value instanceof Behavior ? $value : Yii::createObject($value));//用attachBehavior添加一个行为到组件
return;
} else {//否则
// behavior property
$this->ensureBehaviors();
foreach ($this->_behaviors as $behavior) {
if ($behavior->canSetProperty($name)) {//遍历行为（behaviors），如果行为中有可以设置的属性
$behavior->$name = $value;//给该行为类中的属性设置属性值
return;
}
}
}
if (method_exists($this, 'get' . $name)) {//如果该属性的get方法存在，表名该方法只读，抛出异常
throw new InvalidCallException('Setting read-only property: ' . get_class($this) . '::' . $name);
} else {//否则抛出异常，未知的属性
throw new UnknownPropertyException('Setting unknown property: ' . get_class($this) . '::' . $name);
}
}
/**
* Checks if a property is set, i.e. defined and not null.
* This method will check in the following order and act accordingly:
*
* - a property defined by a setter: return whether the property is set
* - a property of a behavior: return whether the property is set
* - return `false` for non existing properties
*
* 重写 Object 中的 isset 方法，添加对 behaviors 的处理，
* 如果component中不存在该属性，遍历 behaviors，如果其中有相应的属性，就认为有
*
* Do not call this method directly as it is a PHP magic method that
* will be implicitly called when executing `isset($component->property)`.
* @param string $name 属性名或事件名
* @return boolean whether the named property is set
* @see http://php.net/manual/en/function.isset.php
*/
public function __isset($name)
{
$getter = 'get' . $name;
if (method_exists($this, $getter)) {
// 判断是否有getter方法，且是否有返回值，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 $behavior) {//遍历 behaviors
if ($behavior->canGetProperty($name)) {//如果行为（behaviors）中有相应的属性，就认为有
return $behavior->$name !== null;
}
}
}
return false;
}
/**
* Sets a component property to be null.
* 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，添加对 behaviors 的处理
* 如果component中不存在该属性，遍历 behaviors，如果其中有相应的属性，设置为空
*
* 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 $name 属性名
* @throws InvalidCallException if the property is read only.
* @see http://php.net/manual/en/function.unset.php
*/
public function __unset($name)
{
$setter = 'set' . $name;
if (method_exists($this, $setter)) {
// 如果setter方法存在，通过 setter 方法，将它设置为 null
$this->$setter(null);
return;
} else {
// behavior property
$this->ensureBehaviors();
foreach ($this->_behaviors as $behavior) {//否则遍历 behaviors
if ($behavior->canSetProperty($name)) {//如果行为中有相应的属性，设置为空
$behavior->$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.
*
* 重写 Object 中的 call 方法，添加对 behaviors 的处理
* 遍历 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 方法名
* @param array $params 参数
* @return mixed 方法执行后的返回值
* @throws UnknownMethodException when calling unknown method
*/
public function __call($name, $params)
{
$this->ensureBehaviors();//确认行为已经绑定
foreach ($this->_behaviors as $object) {
if ($object->hasMethod($name)) {//调用父类的方法，判断该行为中是否有$name方法
return call_user_func_array([$object, $name], $params);//如果行为中有该方法，则执行该方法
}
}
throw new UnknownMethodException('Calling unknown method: ' . get_class($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.
*
* 在对象克隆clone的时候调用这个方法，将其 _events 和 _behaviors 设置为空
* 当对象被复制后，PHP 5 会对对象的所有属性执行一个浅复制（shallow copy）。
* 所有的引用属性 仍然会是一个指向原来的变量的引用，所以没必要浪费内存
*
*/
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 = [];
$this->_behaviors = null;
}
/**
* Returns a value indicating whether a property is defined for this component.
* A property is defined if:
*
* - the class has a getter or setter method associated with the specified name
* (in this case, property name is case-insensitive);
* - the class has a member variable with the specified name (when `$checkVars` is true);
* - an attached behavior has a property of the given name (when `$checkBehaviors` is true).
*
* 与 Object 中的方法类似，只是添加了是否检测 behavior 的参数
*
* @param string $name the property name
* @param boolean $checkVars whether to treat member variables as properties
* @param boolean $checkBehaviors whether to treat behaviors' properties as properties of this component
* @return boolean whether the property is defined
* @see canGetProperty()
* @see canSetProperty()
*/
public function hasProperty($name, $checkVars = true, $checkBehaviors = true)
{
// $checkVars 参数，用来设置是否局限于是否有 getter/setter
//$checkBehaviors参数，用来设置是否检测behavior
return $this->canGetProperty($name, $checkVars, $checkBehaviors) || $this->canSetProperty($name, false, $checkBehaviors);
}
/**
* Returns a value indicating whether a property can be read.
* A property can be read if:
*
* - the class has a getter method associated with the specified name
* (in this case, property name is case-insensitive);
* - the class has a member variable with the specified name (when `$checkVars` is true);
* - an attached behavior has a readable property of the given name (when `$checkBehaviors` is true).
*
* 检查对象或类是否能够获取 $name 属性，增加了对behavior的检查
*
* @param string $name the property name
* @param boolean $checkVars whether to treat member variables as properties
* @param boolean $checkBehaviors whether to treat behaviors' properties as properties of this component
* @return boolean whether the property can be read
* @see canSetProperty()
*/
public function canGetProperty($name, $checkVars = true, $checkBehaviors = true)
{ // $checkVars 参数，用来设置是否局限于是否有 getter/setter
if (method_exists($this, 'get' . $name) || $checkVars && property_exists($this, $name)) {
return true;
} elseif ($checkBehaviors) {
//$checkBehaviors参数，用来设置是否检测behavior
$this->ensureBehaviors();
foreach ($this->_behaviors as $behavior) {
if ($behavior->canGetProperty($name, $checkVars)) {
return true;
}
}
}
return false;
}
/**
* Returns a value indicating whether a property can be set.
* A property can be written if:
*
* - the class has a setter method associated with the specified name
* (in this case, property name is case-insensitive);
* - the class has a member variable with the specified name (when `$checkVars` is true);
* - an attached behavior has a writable property of the given name (when `$checkBehaviors` is true).
*
* 检查对象或类是否能够设置 $name 属性，增加了对behavior的检查
*
* @param string $name the property name
* @param boolean $checkVars whether to treat member variables as properties
* @param boolean $checkBehaviors whether to treat behaviors' properties as properties of this component
* @return boolean whether the property can be written
* @see canGetProperty()
*/
public function canSetProperty($name, $checkVars = true, $checkBehaviors = true)
{
// $checkVars 参数，用来设置是否局限于是否有 getter/setter
if (method_exists($this, 'set' . $name) || $checkVars && property_exists($this, $name)) {
return true;
} elseif ($checkBehaviors) {//$checkBehaviors参数，用来设置是否检测behavior
$this->ensureBehaviors();
foreach ($this->_behaviors as $behavior) {
if ($behavior->canSetProperty($name, $checkVars)) {//调用父类方法判断
return true;
}
}
}
return false;
}