Initializing @State Properties

In the previous segment, you explored the @State property wrapper, a fundamental tool for managing local state in a SwiftUI view. This segment delves into the crucial aspect of properly initializing @State properties and highlights some common pitfalls to avoid.

When declaring a @State property, it’s very important to initialize it with a default value directly in its declaration. Here’s how the CounterView example from before initializes its count property:

struct CounterView: View {
    @State private var count: Int = 0  // Initial state value is set here

    var body: some View {
        VStack {
            Text("Count: \(count)")
            Button("Increment") {
                count += 1
            }
            Button("Decrement") {
                count -= 1
            }
        }
    }
}

The count property is initialized with a default value of 0.

It is also marked private to prevent external access and modification. @State properties are meant to be managed locally to the view they are declared in. Modifying @State from outside that view could conflict with SwiftUI’s storage management.

What Happens Without an Initial Value?

You might be tempted to set the initial value for a @State property through the view’s initializer. However, this approach can lead to unexpected behavior:

struct CounterView: View {
    @State private var count: Int // No default value

    init(count: Int) {
        self.count = count
    }

    var body: some View {
        VStack {
            Text("Count: \(count)")
            Button("Increment") {
                count += 1
            }
            Button("Decrement") {
                count -= 1
            }
        }
    }
}

In this modified version, the count property is set through an initializer. While this might seem like a valid approach, it introduces a problem. After the view is first created, subsequent updates to the view, even if the count value passed is different, will not affect the @State property. The count property will retain its previous value, and the UI will not reflect any new changes.

Always initialize @State properties with a default value directly in the property declaration. This practice ensures that your views have a consistent starting state and behave as expected.

Using Class vs. Struct Types for @State

For now, avoid using class types for @State until you learn about the Observable macro in Lesson 3. Using class types with @State can lead to unexpected behavior.

Note on State Management in iOS 17

This lesson focuses on state management concepts available in iOS 17 and above. It’s important to note that this lesson doesn’t cover prior state management concepts such as @StateObject. As you progress in your learning journey, you may encounter different state management approaches used in earlier versions of iOS. However, this lesson is tailored to provide you with an understanding of the latest practices in state management with SwiftUI in iOS 17 and beyond.

@State Property Initialization in Action

In the upcoming video demo, you’ll use breakpoints to explore how and when @State properties are initialized. You’ll also get hands-on experience with what happens if a @State property isn’t initialized when it’s declared.