Property observers (willSet, didSet) in Swift - Mini Project: Build & Apply

Using Property Observers (willSet, didSet) in Swift

📖 Scenario: You are creating a simple app to track the temperature of a room. You want to watch the temperature value and print messages whenever it changes.

🎯 Goal: Build a Swift program that uses property observers willSet and didSet to monitor changes to a temperature variable and print messages before and after the change.

📋 What You'll Learn

Create a variable called temperature with an initial value of 20

Add a willSet observer to temperature that prints the new value

Add a didSet observer to temperature that prints the old value

Change the value of temperature to 25

Print the final value of temperature

💡 Why This Matters

🌍 Real World

Property observers are useful in apps that need to react when data changes, like updating the user interface or validating input.

💼 Career

Understanding property observers is important for Swift developers working on iOS apps to manage state and side effects cleanly.

1

Create the temperature variable

Create a variable called temperature and set it to 20.

Swift

# Your code here

Need a hint?

Use var to create a variable and assign 20 to temperature.

2

Add a willSet observer to temperature

Add a willSet observer to the temperature variable that prints "About to set temperature to" followed by the new value using newValue.

Swift

var temperature = 20 {
    // Add willSet observer here
}

Need a hint?

Inside willSet, use print("About to set temperature to \(newValue)").

3

Add a didSet observer to temperature

Add a didSet observer to the temperature variable that prints "Temperature was" followed by the old value using oldValue.

Swift

var temperature = 20 {
    willSet {
        print("About to set temperature to \(newValue)")
    }
    // Add didSet observer here
}

Need a hint?

Inside didSet, use print("Temperature was \(oldValue)").

4

Change temperature and print the final value

Set temperature to 25. Then print the current value of temperature using print(temperature).

Swift

var temperature = 20 {
    willSet {
        print("About to set temperature to \(newValue)")
    }
    didSet {
        print("Temperature was \(oldValue)")
    }
}

// Change temperature and print it
# Your code here

Need a hint?

Assign 25 to temperature and then print it with print(temperature).