无法在ViewController中获取变量

Question

我想从AppDelegate获取ViewController变量，我试过：

//1.
print(ViewController().strName)

//2.
let vc = ViewController()
print(vc.strName)

//3.
let vc = UIApplication.shared.keyWindow!.rootViewController as! ViewController
print(vc.strName)

一切都不起作用，打印值为空......

ViewController中的代码：

var strName : String = ""
override func viewDidLoad() {

    strName = "Tom"

}

Answer 1

我建议检查此链接Swift: How to access in AppDelegate variable from the View controller?否则尝试在视图控制器中，

class ViewController: UIViewController {

  var strName = "someString" // some value

}

在AppDelegate中，

    var mainViewController = ViewController()

func applicationWillEnterForeground(_ application: UIApplication) {
    _ = self.window?.rootViewController as? ViewController
    print(mainViewController.strName)
}

Answer 2

首先，您需要在界面构建器中设置故事板标识符

您需要使用以下代码启动viewcontroller对象。

  let storyboard = UIStoryboard(name: "Main", bundle: Bundle.main)
  let viewcontroller = storyboard.instantiateViewController(withIdentifier: "ViewController") as? ViewController

您可以在此处根据故事板名称更改故事板名称。获得控制器对象后，您可以轻松找到viewcontroller变量。