Error Using Swift - Instance Member Cannot Be Used on Type 'Viewcontroller'

Error: Instance member cannot be used on type 'ViewController'

You are trying to use an instance (cardButtons) of ViewController, which is not initialised. You can use instances of ViewController, once you view controller is loaded, i mean, inside viewDidLoad()

Look at life cycle of UIViewController, to understand issue.

Try this and see:

class ViewController: UIViewController {

    @IBOutlet var cardButtons: [UIButton]!

    var game: Concentration?

    //or 
    //var game: Concentration!

    //or 
    //var game = Concentration()

    //or
    /*
    var game: Concentration {
       return Concentration(numberOfPairsOfCards: cardButtons.count / 2) 
    }
    */
    override func viewDidLoad() {
        super.viewDidLoad()
        game = Concentration(numberOfPairsOfCards: cardButtons.count / 2)
    }

}

Instance member cannot be used on type 'ViewController'

If the code you pasted is not defined in a method like viewDidLoad, you cannot use a variable thats defined at the class level for another variable thats defined at the class level as well. These variables are determined at run time and the order they are determined is not known so fortuneArray may not exist before randomIndex is made (might not really work like this behind the scenes but you can think of it this way at least)

you should compute these variables inside viewDidLoad or init or some other function instead

Instance member ...cannot be used on type ViewController

The accepted answer to the link you have provided explains this issue pretty well, IMHO. Basically, in your example, you are using the three "previously" declared UITextFields in your declaration of ingStackView. However, these four variables are not necessarily determined in that order at runtime. Xcode gives this error because, for example, ingprice may be determined after ingStackView. This is just an example, there is no guarantee in the order.

When you declare each of the variables with lazy var, the error goes away is because according to Apple's Swift Documentation:

A lazy stored property is a property whose initial value is not calculated until the first time it is used. You indicate a lazy stored property by writing the lazy modifier before its declaration.

This means that for lazy variables, all of them are determined at initialization, so you are guaranteed to have all of the four variable values.

Swift 3: Instance Member cannot be used on type “View Controller”

Here's the solution that works :

import UIKit
class ViewController: UIViewController {
@IBOutlet var MyImage: UIImageView!  // Insert Outlet Image : "MyImage"

// Structure ChangeImage
struct ChangeImage {
    private var _isChanged: Bool = false
    private var _myImage: UIImageView!   // Private variable _myImage

    init (ImgView: UIImageView) {        // Initiate ImgView called since func viewDidLoad()
        self._myImage = ImgView          // Private variable _myImage = ImgView ( variable MyImage in func viewDidLoad() )
    }

    mutating func Set_Change(val: Bool) {

        if (val) {
            _myImage.image = UIImage(named: "image2")
            self._isChanged = true
        } else {
            _myImage.image = UIImage(named: "image1")
            self._isChanged = false
        }
    }

    func isChanged()-> Bool {
        return self._isChanged
    }
}

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.

    var MyStruct = ChangeImage(ImgView: MyImage) // Initiate Structure ChangeImage with variable MyImage.
    MyStruct.Set_Change(val: true)
    print (MyStruct.isChanged())
}

}

;)

Error : Instance member cannot be used on type 'ViewController'

Not really sure, but your code should not even compile as your lazy variable instantiation of menubar says

let mbv = MenuBar(

Which it should be

let mbv = MenuBar()

Final working code would be

let menuBarView : MenuBar = {

        let mbv = MenuBar()
        mbv.translatesAutoresizingMaskIntoConstraints = false
        mbv.backgroundColor = UIColor.green
        return mbv
    }()

Tested it, it works absolutely fine.

EDIT:

This is how am using it and it is working fine!

//other variable declaration
    let menuBarView : MenuBar = {
        let mbv = MenuBar()
        mbv.translatesAutoresizingMaskIntoConstraints = false
        mbv.backgroundColor = UIColor.green
        return mbv
    }()

    override func viewDidLoad() {
        super.viewDidLoad()
        self.view.addSubview(menuBarView)

        // Do any additional setup after loading the view, typically from a nib.
    }

Error using Swift - Instance member cannot be used on type 'ViewController'

This code returns a new value every time you call it. I expect it what you're looking for

var myInt: Int? {
    return Int(percentLabel.text!)
}

instead of

let myString = percentLabel
let myInt: Int? = Int(myString)

Instance Member Cannot Be Used on Type when pushing UIViewController

Step 1: Setup your destination class

In CarbonCalculatorResultsViewController class, declare a var to receive data like so:

class CarbonCalculatorResultsViewController: UIViewController {
    var foo: String? {
        didSet {
            // What you'd like to do with the data received
            print(foo ?? "")
        }
    }

    ovevride func viewDidLoad() {
       //
    }
}

Step 2: Prepare data in your source class

let nextViewController = CarbonCalculatorResultsViewController()
// You have access of the variable in CarbonCalculatorResultsViewController
nextViewController.foo = <data_you_want_to_pass>

// Push next View Controller
self.navigationController?.pushViewController(nextViewController, animated: true)

Then, every time the CarbonCalculatorResultsViewController comes alive, the didSet{} of foo would be called.

Instance member cannot be used on type - error

If you need to use the method without an instance, you need to declare the method as static.

static func checkInputs(_ user: Sign, opponent: Sign) -> String

Note: You do not seem to using the user that you pass. IMO you could skip asking for that parameter and use it as an instance method with playerChoice.

func checkInputs(opponent: Sign) -> String {
    // Your logic
}

And then use it like this

playerChoice.checkInputs(opponent: randomSign())

The second error is because you are trying to return an instance of Sign instead of a String. You need to either change the return type to Sign or covert the Sign in outcome to String - outcome.text like @Larme pointed out?

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