定义行为
要定义行为，通过继承 yii\base\Behavior 或其子类来建立一个类。如：
namespace app\components;
use yii\base\Behavior;
class MyBehavior extends Behavior
{
public $prop1;
private $_prop2;
public function getProp2()
{
return $this->_prop2;
}
public function setProp2($value)
{
$this->_prop2 = $value;
}
public function...
