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iOS Intermediate Swift Properties Property Observers

Akos Turi
Akos Turi
7,517 Points
Posted by Akos Turi
Akos Turi
7,517 Points

bit confused

class StepCounter {
    var totalSteps: Int = 0 {
        willSet(newTotalSteps) {
            print("About to set totalSteps to \(newTotalSteps)")
        }
        didSet {
            if totalSteps > oldValue  {
                print("Added \(totalSteps - oldValue) steps")
            }
        }
    }
}

this is from the apple developer documentation. In this example willSet immediately prints the new value, what is the newTotalSteps and the old value is used in the didSet method. In the example what Pasan gave us, according to my interpretation, exactly the opposite happens, because the oldValue is printed out in the willSet method and the newValue is printed in the didSet.

1 Answer

Ramiro H Lopez
Ramiro H Lopez
4,754 Points
Ramiro H Lopez
Ramiro H Lopez
4,754 Points

I was a bit confused as well, but then I realized that the text string that is printing is what is causing the confusion. What is actually being printed out is the "value" variable itself, not the newValue and oldValue that is encapsulated by willSet and didSet.

Try changing the print statement in willSet to:
print("Changing from (value) to newValue: (newValue)")
and didSet to:
print("Changing from oldValue: (oldValue) to (value)")