Question

我正在使用Swift构建iOS应用程序。当我想用segue呈现它们时，我有三个UIViewControllers和一个枚举。

class a: UIViewController {}
class b: UIViewController {}
class c: UIViewController {}

我正在编写一个迭代它们的函数，如果c是当前的那个，那么我需要设置一个属性。然后使用我的a，b，c实例。

// Segues 
func segue(sender: Button) {
    let title = sender.destination!
    switch title {
    case .NewWorkout:
        let VC: NewWorkout = NewWorkout()
    case .Home:
        let VC: Home = Home()
    case .Preview:
        let VC: WorkoutPreview = WorkoutPreview()
        VC.type = .allWorkouts
    } // 1

    self.presentViewController(VC, animated: true, completion: nil) // 2
}

我得到的错误是Expected expression in assignment在第2行的1和Use of unresolved identifier "VC"的行上。我明白我的问题是VC是在switch语句中创建的并且不是在它的独家新闻之外。感谢。

Answer 1

只需在 switch语句之前定义VC变量：

let VC : UIViewController switch title { case .NewWorkout: VC = NewWorkout() case .Home: VC = Home() case .Preview: let workoutPreview = WorkoutPreview() workoutPreview.type = .allWorkouts VC = workoutPreview } self.presentViewController(VC, animated: true, completion: nil)

请注意，您可以使用VC将let声明为（非可选）常量如果在交换机中处理所有可能的枚举值。如有必要，您可以添加

default: fatalError("Unexpected title")

Answer 2

我想你可能会想要这样的东西：

//: Playground - noun: a place where people can play

import UIKit

enum ControllerType {
    case allWorkouts
}

class NewWorkoutController: UIViewController { }
class HomeController: UIViewController { }
class WorkoutPreviewController: UIViewController {
    var type: ControllerType?
}

enum Destination {
    case NewWorkout
    case Home
    case Preview

    var controller: UIViewController {
        switch self {
        case NewWorkout:
            return NewWorkoutController()
        case Home:
            return HomeController()
        case Preview:
            let vc = WorkoutPreviewController()
            vc.type = .allWorkouts
            return vc
        }
    }
}

class Button: UIButton {
    var destination: Destination?
}

class ViewController: UIViewController {
    func segue(sender: Button) {
        if let vc = sender.destination?.controller {
            self.presentViewController(vc, animated: true, completion: nil)
        }
    }
}

Answer 3

您的问题是，您在交换机内声明VC，因此当您使用VC进行预测时，它不知道VC是什么。 VC超出presentViewController的范围。这是你可以做的一种方式：

func segue(sender: Button) {
    let title = sender.destination!
    var VC:UIViewController
    switch title {
        case .NewWorkout:
            VC = NewWorkout()
        case .Home:
            VC = Home()
        case .Preview:
            VC = WorkoutPreview()
            VC.type = .allWorkouts
    } // 1

    self.presentViewController(VC, animated: true, completion: nil) // 2
}

所以现在VC与调用presentViewController的范围相同。

Swift条件绑定

3 个答案: