两个视图控制器之间的协议

Question

我想在两个视图控制器之间使用协议。我试过这样：

protocol ReceivedPhotosDelegate{
    func reloadData()
}

class SecondViewController: UIViewController {
    var recivedDelegate: ReceivedPhotosDelegate?

    override func viewWillAppear(animated: Bool) {
        super.viewWillAppear(animated)
        self.recivedDelegate!.reloadData()
    }
}

第二节课：

class ReceivedPhotosViewController: UIViewController,ReceivedPhotosDelegate {

    func reloadData() {
        print("test ok")
    }
}

当我运行此代码时，我收到以下错误：

fatal error: unexpectedly found nil while unwrapping an Optional value

这一行：

self.recivedDelegate!.reloadData()

如何解决此问题？

Answer 1

在ReceivedPhotosViewController内，你应该设置recievedDelegate。将以下行添加到viewDidLoad

的viewWillAppear或ReceivedPhotosViewController

secondVC.recivedDelegate = self    //assuming secondVC is instance of SecondViewController

所有在调用reloadData时都会检查

if self.recievedDelegate != nil {
    self.recivedDelegate!.reloadData()
}