Question

阅读Emil Atanasov的通过构建应用程序学习Swift ，如果用户已经登录，我正在尝试在应用程序委托中编写代码以在TabbarViewController上启动应用程序（而是比SignInViewController）。但是，尽管为登录屏幕和主视图控制器编写了两个类似的功能（与本书相同），但在加载主视图控制器的功能上却遇到了很多错误-openMainViewController（）

错误： “条件中的模式匹配需要case关键字” “使用未解决的标识符rootViewController”

我已经追溯了这本书，确保标识符在主情节提要中匹配（尽管TabbarViewController没有课程，这是正常现象吗？）

func openSignInScreen() {
    if let signInViewController = self.window?.rootViewController?.storyboard?.instantiateViewController(withIdentifier: "SignInViewController") as? SignInViewController {
        signInViewController.view.frame = (self.window?.rootViewController?.view.frame)!
        signInViewController.view.layoutIfNeeded()
        //nice transition between views
        UIView.transition(with: window!, duration: 0.3, options: .transitionCrossDissolve, animations: {self.window?.rootViewController = signInViewController }, completion: { completed in //nothing to do here
        })
        }
    }
//continue.. now open main View Controller
func openMainViewController() {
    if let rootViewController() = self.window?.rootViewController?.storyboard?.instantiateViewController(withIdentifier: "TabbarViewController") {
            rootViewController().view.frame =  (self.window?.rootViewController?.view.frame)!
            rootViewController().view.layoutIfNeeded()
            //nice transition between views
            UIView.transition(with: window!, duration: 0.3, options: .transitionCrossDissolve, animations: {self.window?.rootViewController = rootViewController() }, completion: { completed in //maybe do something here
        })
    }
}

我希望我编写的代码与书中的代码相同，所以不会出现任何标识问题。但是，我在openMainViewController()函数上遇到了很多错误，而且我对编程总体上还是很陌生的-至今还不知道该怎么去。

Answer 1

我怀疑您在复制书本时出错了

将rootViewController()替换为rootViewController，因为这应该是常量而不是方法。就像在openSignInScreen()

中一样

因此您的更新后的openMainViewController将

func openMainViewController() {
        if let rootViewController = self.window?.rootViewController?.storyboard?.instantiateViewController(withIdentifier: "TabbarViewController") {
            rootViewController.view.frame =  (self.window?.rootViewController?.view.frame)!
            rootViewController.view.layoutIfNeeded()
            //nice transition between views
            UIView.transition(with: window!, duration: 0.3, options: .transitionCrossDissolve, animations: {self.window?.rootViewController = rootViewController }, completion: { completed in //maybe do something here
            })
        }
    }

注意：为此，您应该在故事板上有一个标识符为TabbarViewController的

在应用程序委托中识别和加载视图控制器时出现“使用未解决的标识符'rootViewController'错误”

1 个答案: