我想弄清楚如何创建一个弹出窗口，该窗口仅在您启动该应用程序时出现一次，然后除非您关闭该应用程序并重新启动它，否则不会再次出现。但是，如果您查看下面的代码，您会发现每次 ViewController 出现时都会弹出警报。例如，如果您转到设置选项卡，然后返回主 ViewController，则会弹出警报。

override func viewDidAppear(animated: Bool) { 
    let alertController = UIAlertController(title: "Disclaimer", message: "WARNING: Please ride carefully!", preferredStyle: UIAlertControllerStyle.Alert) 
    alertController.addAction(UIAlertAction(title: "Accept", style: UIAlertActionStyle.Default, handler: nil)) 
    self.presentViewController(alertController, animated: true, completion: nil) 
} 

请您参考如下方法:

只需创建一个 bool 型全局变量。如果打开该应用程序，它会从 false 开始。然后，一旦看到免责声明，它就会将变量设置为 true。然后根据变量的值呈现View Controller。

    var disclaimerHasBeenDisplayed = false 
 
class ViewController { 
 
     override func viewDidAppear(animated: Bool) { 
 
          if disclaimerHasBeenDisplayed == false { 
 
             disclaimerHasBeenDisplayed = true 
 
             let alertController = UIAlertController(title: "Disclaimer", message: "WARNING: Wakeboarding is fun, however it can be highly dangerous. 
     Wake Dice is not liable for any injuries obtained while wakeboarding. Please ride carefully!", preferredStyle: UIAlertControllerStyle.Alert) 
     alertController.addAction(UIAlertAction(title: "Accept", style: UIAlertActionStyle.Default,handler: nil)) 
 
        self.presentViewController(alertController, animated: true, completion: nil) 
    } 
    } 
    }