斯坦福大学 iOS9 2016 年第 6 讲 VCL.swift 文件，错误行 "print("\(logPrefix)Face \(instance)" + msg)"

Question

在 2016 年斯坦福大学第 6 讲 iOS9 系列讲座中，程序中添加了一个名为 VCL.swift 的文件来演示视图控制器生命周期。

我已经添加了文件，但是对于行 "print("\(logPrefix)Emotions\(instance)" + msg) 和行“print("\(logPrefix)Face \(instance)" + msg)"，xcode 显示错误，告诉我 "use of unresolved identifier 'instance' "。

有人知道如何解决吗？

下面是第 6 课VCL.swift 的文件

import UIKit

private var faceMVCinstanceCount = 0
func getFaceMVCinstanceCount() -> Int { faceMVCinstanceCount += 1; return faceMVCinstanceCount }
private var emotionsMVCinstanceCount = 0
func getEmotionsMVCinstanceCount() -> Int { emotionsMVCinstanceCount += 1; return emotionsMVCinstanceCount }

var lastLog = NSDate()
var logPrefix = ""

func bumpLogDepth() {
    if lastLog.timeIntervalSinceNow < -1.0 {
        logPrefix += "__"
        lastLog = NSDate()
    }
}

// we haven't covered extensions as yet
// but it's basically a way to add methods to a given class

extension FaceViewController
{
    func logVCL(msg: String) {
        bumpLogDepth()
        print("\(logPrefix)Face \(instance) " + msg) //error: use of unresolved identifier 'instance'
    }

    override func awakeFromNib() {
        logVCL("awakeFromNib()")
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        logVCL("viewDidLoad()")
    }
    override func viewWillAppear(animated: Bool) {
        super.viewWillAppear(animated)
        logVCL("viewWillAppear(animated = \(animated))")
    }
    override func viewDidAppear(animated: Bool) {
        super.viewDidAppear(animated)
        logVCL("viewDidAppear(animated = \(animated))")
    }
    override func viewWillDisappear(animated: Bool) {
        super.viewWillDisappear(animated)
        logVCL("viewWillDisappear(animated = \(animated))")
    }
    override func viewDidDisappear(animated: Bool) {
        super.viewDidDisappear(animated)
        logVCL("viewDidDisappear(animated = \(animated))")
    }

    override func viewWillLayoutSubviews() {
        super.viewWillLayoutSubviews()
        logVCL("viewWillLayoutSubviews() bounds.size = \(view.bounds.size)")
    }
    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()
        logVCL("viewDidLayoutSubviews() bounds.size = \(view.bounds.size)")
    }

    override func viewWillTransitionToSize(size: CGSize, withTransitionCoordinator coordinator: UIViewControllerTransitionCoordinator) {
        super.viewWillTransitionToSize(size, withTransitionCoordinator: coordinator)
        logVCL("viewWillTransitionToSize")
        coordinator.animateAlongsideTransition({ (context: UIViewControllerTransitionCoordinatorContext!) -> Void in
            self.logVCL("animatingAlongsideTransition")
            }, completion: { context -> Void in
                self.logVCL("doneAnimatingAlongsideTransition")
        })
    }
}

extension EmotionsViewController
{
    func logVCL(msg: String) {
        bumpLogDepth()
        print("\(logPrefix)Emotions \(instance) " + msg) //error: use of unresolved identifier 'instance'
    }

    override func awakeFromNib() {
        logVCL("awakeFromNib()")
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        logVCL("viewDidLoad()")
    }
    override func viewWillAppear(animated: Bool) {
        super.viewWillAppear(animated)
        logVCL("viewWillAppear(animated = \(animated))")
    }
    override func viewDidAppear(animated: Bool) {
        super.viewDidAppear(animated)
        logVCL("viewDidAppear(animated = \(animated))")
    }
    override func viewWillDisappear(animated: Bool) {
        super.viewWillDisappear(animated)
        logVCL("viewWillDisappear(animated = \(animated))")
    }
    override func viewDidDisappear(animated: Bool) {
        super.viewDidDisappear(animated)
        logVCL("viewDidDisappear(animated = \(animated))")
    }

    override func viewWillLayoutSubviews() {
        super.viewWillLayoutSubviews()
        logVCL("viewWillLayoutSubviews() bounds.size = \(view.bounds.size)")
    }
    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()
        logVCL("viewDidLayoutSubviews() bounds.size = \(view.bounds.size)")
    }

    override func viewWillTransitionToSize(size: CGSize, withTransitionCoordinator coordinator: UIViewControllerTransitionCoordinator) {
        super.viewWillTransitionToSize(size, withTransitionCoordinator: coordinator)
        logVCL("viewWillTransitionToSize")
        coordinator.animateAlongsideTransition({ (context: UIViewControllerTransitionCoordinatorContext!) -> Void in
            self.logVCL("animatingAlongsideTransition")
            }, completion: { context -> Void in
                self.logVCL("doneAnimatingAlongsideTransition")
        })
    }
}

Answer 1

错误："use of unresolved identifier 'instance'" 表示您正在尝试使用尚未声明的变量。

在您的情况下，EmotionsViewController (EmotionsViewController.swift) and/or let instance = getFaceMVCinstanceCount() FaceViewController ( FacialExpression.swift).

只需查看此处提供的完整资源： Lecture 6: Multiple MVCs

Answer 2

该错误意味着您正在尝试打印 instance 但您没有在任何地方的代码中定义它。两次检查您的代码，您的对象或变量是否带有 instance 标识符。

希望这会有所帮助:)

斯坦福大学 iOS9 2016 年第 6 讲 VCL.swift 文件，错误行 "print("\(logPrefix)Face \(instance)" + msg)"

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