First iOS app in iOS Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

What will this SwiftUI code display?

Consider this SwiftUI view code. What text will appear on the screen when the app runs?

iOS Swift

import SwiftUI

struct ContentView: View {
  var body: some View {
    Text("Welcome to my first app!")
      .font(.title)
      .foregroundColor(.blue)
  }
}

A A large red text saying 'Welcome to my first app!'

B A small blue text saying 'Welcome to my first app!'

C A large blue text saying 'Welcome to my first app!'

D No text appears because of a syntax error

💡 Hint

Look at the modifiers .font(.title) and .foregroundColor(.blue).

The Text view shows the string with a title font size and blue color as specified.

❓ navigation

intermediate

What happens when this button is tapped?

This SwiftUI code shows a button inside a NavigationView. What happens when the user taps the button?

iOS Swift

import SwiftUI

struct ContentView: View {
  var body: some View {
    NavigationView {
      NavigationLink("Go to Details", destination: Text("Details Screen"))
        .navigationTitle("Home")
    }
  }
}

A The button shows an alert instead of navigating.

B The button does nothing because NavigationLink is missing an action.

C The app crashes due to missing navigation controller.

D The app navigates to a new screen showing 'Details Screen' text.

💡 Hint

NavigationLink creates a tappable link to a destination view.

Tapping the NavigationLink navigates to the destination view showing 'Details Screen'.

❓ lifecycle

advanced

When is the body property of a SwiftUI View recomputed?

Given this SwiftUI view with a @State variable, when does the body property get recomputed?

iOS Swift

import SwiftUI

struct ContentView: View {
  @State private var count = 0

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

A Only when the app restarts.

B Each time the count variable changes, the body recomputes to update the UI.

C Every second automatically, regardless of state changes.

D Only once when the view is created; state changes do not affect body.

💡 Hint

Think about how @State triggers UI updates.

Changing a @State variable causes SwiftUI to recompute the body to reflect UI changes.

📝 Syntax

advanced

What error does this SwiftUI code produce?

Examine this SwiftUI code snippet. What error will it cause when compiling?

iOS Swift

import SwiftUI

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

A Runtime error: count variable not initialized.

B No error; code runs fine.

C Syntax error: Missing closure for Button action.

D Type error: Text cannot be inside VStack.

💡 Hint

Check the Button syntax and its action closure.

Button requires an action closure after the label; missing closure causes syntax error.

🔧 Debug

expert

Why does this SwiftUI view not update the text when the button is tapped?

This code intends to update the displayed text when the button is tapped, but it does not. Why?

iOS Swift

import SwiftUI

struct ContentView: View {
  var count = 0

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

A Because count is a regular variable, not a @State property, so changes don't trigger UI updates.

B Because the Button label is incorrect and does not trigger the action.

C Because the Text view is outside the VStack.

D Because the count variable is declared as a constant.

💡 Hint

Think about how SwiftUI tracks changes to update the UI.

Only @State properties trigger UI updates when changed; regular vars do not.