core/Controller.php
protected function display(string $tplName, string $parent = null)
    {
        $this->view()->context($this);
        $this->setContentType('html');
        if ($parent !== null) {
            return $this->view()->display($this, 'extends:' . $parent . '|' . $tplName);
        }
        return $this->view()->display($tplName);
    }
protected function display(string $tplName, string $parent = null)
    {
        $this->view()->context($this);
        $this->setContentType('html');
        if ($parent !== null) {
            return $this->view()->display($this, 'extends:' . $parent . '|' . $tplName);
        }
        return $this->view()->display($tplName);
    }
输出显示
@param string $tplName
@param string|null $parent