Ios 在Swift中向通知中添加if语句

现在，当应用程序加载时，我的代码会立即显示一条警告消息。我想将代码更改为仅显示警报消息。如果在加载后20秒内未按下按钮。按钮操作称为

按按钮

import UIKit

class ViewController: UIViewController {

let myNotification = Notification.Name(rawValue:"MyNotification")

override func viewDidLoad() {
    super.viewDidLoad()

    let nc = NotificationCenter.default
    nc.addObserver(forName:myNotification, object:nil, queue:nil, using:catchNotification)
}
    @IBAction func pressBUTTON(_ sender: Any) {
    }

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)
    let nc = NotificationCenter.default
    nc.post(name:myNotification,
            object: nil,
            userInfo:["message":"Hello there!", "date":Date()])
}

func catchNotification(notification:Notification) -> Void {
    print("Catch notification")

    guard let userInfo = notification.userInfo,
        let message  = userInfo["message"] as? String,
        let date     = userInfo["date"]    as? Date else {
            print("No userInfo found in notification")
            return
    }

    let alert = UIAlertController(title: "Notification!",
                                  message:"\(message) received at \(date)",
        preferredStyle: UIAlertControllerStyle.alert)
    alert.addAction(UIAlertAction(title: "OK", style: UIAlertActionStyle.default, handler: nil))
    self.present(alert, animated: true, completion: nil)
}}

---

将您的警报代码包装在一个不重复的

计时器中，延迟20秒。在您的
按钮
功能中，在该计时器上调用
无效
，以禁止显示通知

在离开视图控制器时（例如，在
viewWillDisapear
方法中），使计时器失效可能是一个好主意