无法在 ViewController 中获取变量

Question

我想从 AppDelegate 获取 ViewController 变量，我试过了：

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

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

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

全部不工作，打印值为空...

ViewController中的代码：

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

    strName = "Tom"

}

Answer 1

我建议检查一下这个 link Swift: How to access in AppDelegate variable from the View controller? 否则在视图控制器中尝试，

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)
}

无法在 ViewController 中获取变量

Can't get variable in ViewController

xcode

appdelegate

swift4