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iOS Intermediate Swift Properties Property Observers

Gene Bogdanovich
Gene Bogdanovich
14,618 Points
Posted by Gene Bogdanovich
Gene Bogdanovich
14,618 Points

Property Observers Code Challenge in Intermediate Swift 3

I have no idea how to make it work. Please help!

observer.swift 
class TemperatureController: UIViewController {
    var temperature: Double {
        didSet(newValue) {
          if newValue > 80.0 {
          super.viewDidLoad()
              view.backgroundColor = UIColor.red
          } else if newValue < 40.0 {
          super.viewDidLoad()
              view.backgroundColor = UIColor.blue
          } else {
          super.viewDidLoad()
              view.backgroundColor = UIColor.green

          }

        }
    }

    init(temperature: Double) {
        self.temperature = temperature
        super.init()
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .white
    }
}
akyya mayberry
akyya mayberry
3,668 Points

Also to note, I think if you specify a named argument for didSet as you did 'newValue' it actually holds the previous value (the old value) of temperature not the current temp. didSet is triggered when a change is done to temperature. didSet has the old value (oldValue or in your code newValue) and access to the new value (temperature). This is from Swift docs,

Similarly, if you implement a didSet observer, it’s passed a constant parameter containing the old property value. You >can name the parameter or use the default parameter name of oldValue. If you assign a value to a property within its >own didSet observer, the new value that you assign replaces the one that was just set.

1 Answer

Dan Lindsay
Dan Lindsay
39,611 Points
Dan Lindsay
Dan Lindsay
39,611 Points

Hey Eugene,

It looks like you are making it more complicated than it has to be. We don't have to worry about creating a newValue variable here, and super.viewDidLoad() only needs to be called once inside the viewDidLoad() method. Use temperature as the value you are comparing if greater than or less than, and you should pass the challenge. This worked for me:

class TemperatureController: UIViewController {
    var temperature: Double {
        didSet {
            if temperature > 80.0 {
                view.backgroundColor = UIColor.red
            } else if temperature < 40 {
                view.backgroundColor = UIColor.blue
            } else {
                view.backgroundColor = UIColor.green
            }
        }
    }

    init(temperature: Double) {
        self.temperature = temperature
        super.init()
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .white
    }
}

Hope this helps!

Dan

Cameron Hyatt
Cameron Hyatt
5,948 Points
Cameron Hyatt
Cameron Hyatt
5,948 Points

I tried using a switch inside the didSet for mine but it was giving me errors about Bool and Double types. Maybe I'm forgetting something because I've been away too long but wouldn't the switch statement work instead of an if-else statement?