设置amountToRelad var的值，以便可以在类的任何方法上访问它

我在一个OctoberCMS组件中工作，在工作时遇到了一些问题。看看这个代码：

class Payment extends ComponentBase
{
    /**
     * This hold the amount with PayPal fee and discount applied and pass back to template
     * @var float
     */
    public $amountToReload;
    public function onAmountChange()
    {
        $amount = post('amount');
        if (empty($amount)) {
            throw new 'Exception(sprintf('Por favor introduzca un valor.'));
        }
        $this->amountToReload = round($amount - ($amount * (float) Settings::get('ppal_fee') - (float) Settings::get('ppal_discount')), 2);
        return ['#amountToReload' => $this->amountToReload];
    }
    public function onRun()
    {
        $step = $this->param('step');
        $sandboxMode = Settings::get('sandbox_enabled');
        switch ($step) {
            case "step2":
                echo $this->amountToReload;
                $params = [
                    'username' => $sandboxMode ? Settings::get('ppal_api_username_sandbox') : Settings::get('ppal_api_username'),
                    'password' => $sandboxMode ? Settings::get('ppal_api_password_sandbox') : Settings::get('ppal_api_password'),
                    'signature' => $sandboxMode ? Settings::get('ppal_api_signature_sandbox') : Settings::get('ppal_api_signature'),
                    'testMode' => $sandboxMode,
                    'amount' => $this->amountToReload,
                    'cancelUrl' => 'www.xyz.com/returnUrl', // should point to returnUrl method on this class
                    'returnUrl' => 'www.xyz.com/cancelUrl', // should point to cancelUrl method on this class
                    'currency' => 'USD'
                ];
                $response = Omnipay::purchase($params)->send();
                if ($response->isSuccessful()) {
                    // payment was successful: update database
                    print_r($response);
                } elseif ($response->isRedirect()) {
                    // redirect to offsite payment gateway
                    return $response->getRedirectResponse();
                } else {
                    // payment failed: display message to customer
                    echo $response->getMessage();
                }
                break;
            default:
                break;
        }
        $this->page['step'] = $step;
    }
    public function cancelPayment()
    {
       // handle payment cancel   
    }
}

如果我在类的顶部有$amountToReload作为公共声明的var，并在onAmountChange()方法中为其设置值？那么在onRun()方法中，这个var不应该保持它的设置值吗？为什么它到达NULL或没有值？我是来自Symfony的Laravel的新手。保持var值的最佳方法是什么，这样我就可以在整个类中使用它而不会出现问题？

作为这篇文章的第二部分，我需要为cancelPayment()方法生成一个有效的路由，这将在以下行中进行：

'returnUrl' => 'www.xyz.com/cancelUrl', // should point to cancelUrl method on this class

如何在Laravel中创建一个可能带有参数的有效URL？使用URL帮助程序？使用路线？哪一个？