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iOS Intermediate Swift 2 Properties Property Observers

Posted by Mazvydas Bartasius
Mazvydas Bartasius
2,359 Points

Having troubles with property observers. Need help to solve the challange

Can't seem to wrap my head around the concept.

In the editor, I've created a UIViewController subclass, TemperatureController that contains a single property - temperature. Your task is to add a didSet property observer to temperature and set the view's background color depending on value of the temperature. For example, if the temperature is greater than 80, set the view's background color to UIColor.redColor(). Similarly if the temperature is less than 40, set it to blue color, otherwise set it to green color. Note: For changing the view's background color, there's example code in viewDidLoad()

observer.swift 
class TemperatureController: UIViewController {
    var temperature: Double


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

    override func viewDidLoad() {
        view.backgroundColor = UIColor.whiteColor()
    }
}

1 Answer

Tobias Helmrich
Tobias Helmrich
31,602 Points
Tobias Helmrich
Tobias Helmrich
31,602 Points

Hey there,

to add a property observer to a stored property you have to write the observer inside of curly braces after the property you want to observe, in this case it's temperature . After that you have to write the code that should be executed each time when the property changed (because we're using didSet here) inside of curly braces after the observer.

In this case the code inside of the property observer's body should check the temperature and change the background color of the view depending on its value. You can check the different cases with an if, else if and else clause and then give the background a color by using the code you can already see in the viewDidLoad method.

Like so:

class TemperatureController: UIViewController {
    var temperature: Double {
        didSet {
            if temperature > 80 {
                view.backgroundColor = UIColor.redColor()
            } else if temperature < 40 {
                view.backgroundColor = UIColor.blueColor()
            } else {
                view.backgroundColor = UIColor.greenColor()
            }
        }
    }

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

    override func viewDidLoad() {
        view.backgroundColor = UIColor.whiteColor()
    }
}

I hope that helps, if you have further questions feel free to ask! :)

Mazvydas Bartasius
Mazvydas Bartasius
2,359 Points

Thanks, my solution was identical, just had a typo. At least I was on the right track.