Property observers (willSet, didSet) in Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a property observer that runs before the value changes.

Swift

var score: Int = 0 {
    [1] {
        print("Score will change to \(newValue)")
    }
}

Drag options to blanks, or click blank then click option'

Aget

BdidSet

Cset

DwillSet

Attempts:

3 left

💡 Hint

Common Mistakes

Using didSet instead of willSet, which runs after the value changes.

The willSet observer runs just before the property value changes.

2fill in blank

medium

Complete the code to print the old value after the property changes.

Swift

var level: Int = 1 {
    didSet {
        print("Level changed from \([1]) to \(level)")
    }
}

Drag options to blanks, or click blank then click option'

AoldValue

Blevel

CnewValue

Dself

Attempts:

3 left

💡 Hint

Common Mistakes

Using newValue inside didSet, which is not available there.

The didSet observer runs after the value changes and provides oldValue to access the previous value.

3fill in blank

hard

Fix the error in the property observer to correctly access the new value.

Swift

var health: Int = 100 {
    willSet {
        print("Health will be set to \([1])")
    }
}

Drag options to blanks, or click blank then click option'

AoldValue

BnewValue

Cself

Dhealth

Attempts:

3 left

💡 Hint

Common Mistakes

Using oldValue or the property name instead of newValue in willSet.

Inside willSet, newValue holds the value about to be set.

4fill in blank

hard

Fill both blanks to create a property observer that prints old and new values.

Swift

var temperature: Double = 20.0 {
    willSet {
        print("Temperature will change from \([1]) to \([2])")
    }
}

Drag options to blanks, or click blank then click option'

Atemperature

BoldValue

CnewValue

Dself

Attempts:

3 left

💡 Hint

Common Mistakes

Using oldValue in willSet, which is not available.

In willSet, the current value is accessed by the property name, and the new value is newValue.

5fill in blank

hard

Fill all three blanks to create a didSet observer that prints old and new values and updates a label.

Swift

var progress: Int = 0 {
    didSet {
        print("Progress changed from \([1]) to \([2])")
        progressLabel.text = "Progress: \([3])%"
    }
}

Drag options to blanks, or click blank then click option'

AoldValue

Bprogress

DnewValue

Attempts:

3 left

💡 Hint

Common Mistakes

Using newValue inside didSet, which is not available.

In didSet, oldValue is the previous value, and the property name progress holds the new value.