src/Controller.php
protected function goBack(string $url = ''): void
    {
        if (!$url) {
            $url = $this->getBack();
        }
        unset($_SESSION['_BACK_URL']);
        header('Location: ' . $url);

        ($this->callback)($this);
    }
protected function goBack(string $url = ''): void
    {
        if (!$url) {
            $url = $this->getBack();
        }
        unset($_SESSION['_BACK_URL']);
        header('Location: ' . $url);

        ($this->callback)($this);
    }
返回用 setBack() 设置的 URL
@param $url string 可以强行指定一个URL