可以使用PKPaymentAuthorizationViewController的delegate方法来捕捉支付未完成的事件。具体实现如下：

1.在控制器中设置PKPaymentAuthorizationViewControllerDelegate：

class ViewController: UIViewController, PKPaymentAuthorizationViewControllerDelegate { // ... }

2.在启动Apple Pay时，设置自己为PKPaymentAuthorizationViewController的delegate：

let paymentVC = PKPaymentAuthorizationViewController(paymentRequest: paymentRequest) paymentVC.delegate = self self.presentViewController(paymentVC, animated: true, completion: nil)

3.实现delegate中的paymentAuthorizationViewController(_: didAuthorizePayment: handler:)方法来捕捉支付完成事件：

func paymentAuthorizationViewController(controller: PKPaymentAuthorizationViewController, didAuthorizePayment payment: PKPayment, handler completion: (PKPaymentAuthorizationStatus) -> Void) { // Here you can handle the case where payment is complete completion(PKPaymentAuthorizationStatus.Success) }

4. 实现delegate中的paymentAuthorizationViewControllerDidFinish(_:)方法来处理支付未完成的事件：

func paymentAuthorizationViewControllerDidFinish(controller: PKPaymentAuthorizationViewController) { // Here you can handle the case where payment is not complete controller.dismissViewControllerAnimated(true, completion: nil) }

这样，在用户在Apple Pay界面中主动关闭支付或者支付出现任何问题导致支付未完成时，上述的paymentAuthorizationViewControllerDidFinish函数将被调用，您就可以在其中进行相关处理了。