Question

我希望在应用程序打开时立即运行条件if语句。基本上，它将是

if x = true {
  //segue to viewcontroller1
} else {
  //stay on this page
}

这将在Xcode中并以swift编码（显然语法错误）...如果条件为真，则将语法写入segue到特定视图控制器的适当方法是什么，并保持正常的方式打开应用程序后打开了吗？另外，我在哪里放这个？我通常在第一次显示的viewcontroller中考虑了viewdidload方法，但是在视图加载之前需要检查变量，这样如果条件为真且那个，视图就会变为另一个变量。首先打开？

编辑：我尝试按如下方式设置AppDelegate.swift中的代码：

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
        if x{
            let mainStoryBoard = UIStoryboard(name: "Main", bundle: nil)
            let ViewController = mainStoryBoard.instantiateViewController(withIdentifier: "ViewController") as! ViewController
            let appDelegate = UIApplication.shared.delegate as! AppDelegate
            appDelegate.window?.rootViewController = ViewController
        } else{
          //same code as above but to different VC
        }
        return true
    }

但是当我运行这个时，我在appDelegate中得到一个错误，说＆＃34; libc ++ abi.dylib：以NSException类型的未捕获异常终止＆＃34;。修改此代码的正确方法是什么？

Answer 1

如果要在演示前选择场景。您可以在appDelegate.swift中的application(application: UIApplication, didFinishLaunchingWithOptions)中添加以下内容：

var id = x ? "id1" : "id2"

self.window = UIWindow(frame: UIScreen.main.bounds)
let mainStoryboard: UIStoryboard = UIStoryboard(name: "Main", bundle: nil)
let exampleVC: UIViewController = mainStoryboard.instantiateViewController(withIdentifier: id) as UIViewController
self.window?.rootViewController = exampleVC
self.window?.makeKeyAndVisible()

确保在故事板中命名场景

如果您在第一个场景显示然后选择要进行调整时表现良好：

if x {
  self.performSegue(withIdentifier: "id1", sender: self)       
} else {
  self.performSegue(withIdentifier: "id2", sender: self)
}

再次确保在故事板中命名segues

另一种选择，使用UINavigationController。将导航控制器设置为根视图控制器

let id = x ? "id1" : "id2"

let mainStoryboard = UIStoryboard(name: "MainStoryboard", bundle: nil)
let exampleVC = mainStoryboard.instantiateViewController(withIdentifier: id) as UIViewController
let navigationController = UINavigationController(rootViewController: exampleVC)
self.window = UIWindow(frame: UIScreen.main.bounds)
self.window!.rootViewController = navigationController
self.window!.makeKeyAndVisible()

使用if else条件语句

1 个答案: