为什么我们通过箭头符号' - >'从那个子对象调用Yii2静态组件方法？

In normal way, I know that we can call parent static method with :: sign but it seems that in Yii2 Framework, we should call static components method via arrow sign (object operator).

I'd like to know how its possible?

For example, in

$foo->on(Foo::EVENT_HELLO, 'function_name');

on() is an static method of yii\base\component but we call it with arrow.

Component::on() is not static:

public function on($name, $handler, $data = null, $append = true)
{
    $this->ensureBehaviors();
    if (strpos($name, '*') !== false) {
        if ($append || empty($this->_eventWildcards[$name])) {
            $this->_eventWildcards[$name][] = [$handler, $data];
        } else {
            array_unshift($this->_eventWildcards[$name], [$handler, $data]);
        }
        return;
    }
    if ($append || empty($this->_events[$name])) {
        $this->_events[$name][] = [$handler, $data];
    } else {
        array_unshift($this->_events[$name], [$handler, $data]);
    }
}

https://github.com/yiisoft/yii2/blob/bc9a82ff80e0abc3ce1430310d2b9b1f70f18c62/framework/base/Component.php#L514

Event::on() is static:

public static function on($class, $name, $handler, $data = null, $append = true)
{
    $class = ltrim($class, '\\');
    if (strpos($class, '*') !== false || strpos($name, '*') !== false) {
        if ($append || empty(self::$_eventWildcards[$name][$class])) {
            self::$_eventWildcards[$name][$class][] = [$handler, $data];
        } else {
            array_unshift(self::$_eventWildcards[$name][$class], [$handler, $data]);
        }
        return;
    }
    if ($append || empty(self::$_events[$name][$class])) {
        self::$_events[$name][$class][] = [$handler, $data];
    } else {
        array_unshift(self::$_events[$name][$class], [$handler, $data]);
    }
}

https://github.com/yiisoft/yii2/blob/bc9a82ff80e0abc3ce1430310d2b9b1f70f18c62/framework/base/Event.php#L103

But I've never seen that someone is using it in non-static way.