@State property wrapper in iOS Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

What happens when you tap the button?

Consider this SwiftUI code snippet using @State. What will the Text display after tapping the button once?

iOS Swift

struct ContentView: View {
  @State private var count = 0
  var body: some View {
    VStack {
      Text("Count: \(count)")
      Button("Tap me") {
        count += 1
      }
    }
  }
}

A The Text updates to show "Count: 1"

B The Text stays at "Count: 0" because @State does not update UI

C The app crashes because count is immutable

D The Text shows "Count: 0" but the button becomes disabled

💡 Hint

Remember that @State allows the view to update when the variable changes.

The @State property wrapper marks the variable as mutable state for the view. When the button increments count, SwiftUI re-renders the view and updates the Text to show the new value.

❓ lifecycle

intermediate

Where should @State variables be declared?

Which of these is the correct place to declare an @State variable in a SwiftUI view?

A Inside the body property of the View

B As a private property inside the View struct, outside the body

C In the AppDelegate class

D Inside the Button action closure

💡 Hint

Think about where properties live in a struct.

@State variables must be declared as properties of the View struct, outside the body property. Declaring inside body or closures is invalid.

📝 Syntax

advanced

What error does this code produce?

What error will this SwiftUI code cause?

iOS Swift

struct ContentView: View {
  @State var name: String
  var body: some View {
    Text("Hello, \(name)!")
  }
}

A No error, code runs fine

B Cannot use @State with String type

C Missing body property error

D Property 'name' must have an initial value or be optional

💡 Hint

Check how @State variables must be initialized.

@State variables must have an initial value because SwiftUI manages their storage. Declaring without initialization causes a compile error.

🔧 Debug

advanced

Why does the UI not update?

Given this code, why does the Text not update when the button is tapped?

iOS Swift

struct ContentView: View {
  var count = 0
  var body: some View {
    VStack {
      Text("Count: \(count)")
      Button("Tap") {
        count += 1
      }
    }
  }
}

A Because the Button action is empty and does not change count

B Because the Text view is outside the VStack

C Because 'count' is not marked with @State, so changes don't trigger UI updates

D Because 'count' is a constant and cannot be changed

💡 Hint

Think about what triggers SwiftUI to refresh the view.

Without @State, changing 'count' does not notify SwiftUI to update the UI. The variable is just a normal property and changes are ignored for UI refresh.

🧠 Conceptual

expert

What is the role of @State in SwiftUI?

Which statement best describes the purpose of the @State property wrapper in SwiftUI?

A @State stores mutable data owned by a view and triggers UI updates when changed

B @State is used to declare constants that never change

C @State shares data between multiple views without copying

D @State manages network requests asynchronously

💡 Hint

Consider how SwiftUI knows when to redraw a view.

@State marks data that belongs to a view and can change over time. When the data changes, SwiftUI automatically refreshes the view to reflect the new state.