Tony Stark Tony Stark - 6 months ago 55
Swift Question

stanford ios9 2016 lecture 6 VCL.swift file, errors with line "print("\(logPrefix)Face \(instance)" + msg)"

In lecture 6 stanford ios9 2016 lecture series, a file called VCL.swift was added to the program to demonstrate view controller lifecycle.

I have added the file, but for line

"print("\(logPrefix)Emotions\(instance)" + msg)
and line "
print("\(logPrefix)Face \(instance)" + msg)"
, xcode is displaying an error, telling me that "use of unresolved identifier 'instance' ".

Does anyone has any idea how to fix it? Thanks in advance for any help and suggestions!

Below is the VCL.swift file from lecture 6

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

The error: "use of unresolved identifier 'instance'" means that you are trying to use a variable, that hasn't been declared.

In your case you are lacking a line let instance = getEmotionsMVCinstanceCount() in the EmotionsViewController (EmotionsViewController.swift) and/or let instance = getFaceMVCinstanceCount() in the FaceViewController (FacialExpression.swift).

Just take a look on a full source available here: Lecture 6: Multiple MVCs

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