First iOS app in iOS Swift

Introduction

Making your first iOS app helps you learn how to create simple apps that run on iPhones. It shows you how to display text and respond to user actions.

You want to create a simple app that shows a greeting message.

You want to learn how to build apps that run on iPhones.

You want to understand the basics of app structure and user interface.

You want to test how to add buttons and text on the screen.

You want to start a project that can grow into a bigger app later.

Syntax

iOS Swift

import SwiftUI

@main
struct MyFirstApp: App {
  var body: some Scene {
    WindowGroup {
      ContentView()
    }
  }
}

struct ContentView: View {
  var body: some View {
    Text("Hello, world!")
      .padding()
  }
}

The @main attribute marks the app's entry point.

ContentView defines what the user sees on the screen.

Examples

This shows a blue title text on the screen.

iOS Swift

Text("Welcome to my app!")
  .font(.title)
  .foregroundColor(.blue)

This creates a button that prints a message when tapped.

iOS Swift

Button("Tap me") {
  print("Button tapped")
}

Sample App

This app shows a large greeting text and a blue button below it. When you tap the button, it prints a message in the console.

iOS Swift

import SwiftUI

@main
struct MyFirstApp: App {
  var body: some Scene {
    WindowGroup {
      ContentView()
    }
  }
}

struct ContentView: View {
  var body: some View {
    VStack {
      Text("Hello, world!")
        .font(.largeTitle)
        .padding()
      Button("Tap me") {
        print("Button was tapped")
      }
      .padding()
      .background(Color.blue)
      .foregroundColor(.white)
      .cornerRadius(8)
    }
  }
}

Important Notes

Use the Xcode simulator to see your app running on a virtual iPhone.

Remember to check the console to see print messages when you tap buttons.

Start simple and add more features as you learn.

Summary

Your first iOS app shows text and a button on the screen.

Use Text to display words and Button to handle taps.

The @main struct starts your app and shows the main view.

Practice

1. What does the Text view do in a basic SwiftUI iOS app?

easy

A. It displays a string of text on the screen.

B. It creates a button that can be tapped.

C. It starts the app when launched.

D. It handles user input from the keyboard.

Solution

1. Step 1: Understand the role of Text in SwiftUI

   The Text view is used to show words or sentences on the screen.

2. Step 2: Differentiate from other views

   Unlike Button, which handles taps, Text only displays static text.

3. Final Answer:

   It displays a string of text on the screen. -> Option A

4. Quick Check:

   Text shows text [OK]

Hint: Remember: Text shows words, Button reacts to taps [OK]

Common Mistakes:

• Confusing Text with Button
• Thinking Text starts the app
• Assuming Text handles user input

2. Which of the following is the correct way to create a button with the label "Tap me" in SwiftUI?

easy

A. Button("Tap me") { print("Tapped") }

B. Button(Text("Tap me")) { print("Tapped") }

C. Button { print("Tapped") } label: { Text("Tap me") }

D. Button(action: print("Tapped"), label: "Tap me")

Solution

1. Step 1: Recall SwiftUI Button syntax

   The correct syntax uses a trailing closure for the action and a label closure for the button text.

2. Step 2: Match syntax to options

   Button { print("Tapped") } label: { Text("Tap me") } matches the correct pattern: Button { action } label: { Text("label") }.

3. Final Answer:

   Button { print("Tapped") } label: { Text("Tap me") } -> Option C

4. Quick Check:

   Button syntax uses closures for action and label [OK]

Hint: Button uses closures: action first, label second [OK]

Common Mistakes:

• Using Button with string only as label
• Putting action inside label
• Incorrect parameter order

3. What will be displayed when this SwiftUI code runs?

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

medium

A. A text showing "Count: 0" and a button labeled "Increment" that increases count when tapped.

B. Only a button labeled "Increment" with no text displayed.

C. A text showing "Count: 1" initially and a button labeled "Increment".

D. The app will crash due to missing @State annotation.

Solution

1. Step 1: Understand @State usage

   The variable count is marked with @State, so changes update the UI.

2. Step 2: Analyze initial UI

   Initially, count is 0, so text shows "Count: 0" and button labeled "Increment" is visible.

3. Final Answer:

   A text showing "Count: 0" and a button labeled "Increment" that increases count when tapped. -> Option A

4. Quick Check:

   @State variable updates UI on change [OK]

Hint: @State variables start at initial value and update UI [OK]

Common Mistakes:

• Thinking count starts at 1
• Assuming no text is shown
• Believing app crashes without @State

4. Identify the error in this SwiftUI code snippet:

struct ContentView: View {
  var body: some View {
    Button("Click me") {
      print("Clicked")
    }
  }
}

medium

A. The body property must return some View explicitly.

B. No syntax error; the code is correct.

C. The body property must be marked with @ViewBuilder.

D. The Button label should be a closure, not a string.

Solution

1. Step 1: Check body property syntax

   In SwiftUI, the body computed property implicitly returns the view using @ViewBuilder.

2. Step 2: Verify the Button syntax

   Button("Click me") { print("Clicked") } is valid; no explicit return needed even for multi-line expressions.

3. Final Answer:

   No syntax error; the code is correct. -> Option B

4. Quick Check:

   SwiftUI body implicitly returns views [OK]

Hint: SwiftUI body uses implicit return via ViewBuilder [OK]

Common Mistakes:

• Thinking an explicit return is required
• Believing @ViewBuilder must be marked explicitly
• Assuming Button requires closure label only

5. You want to create a simple iOS app that shows "Hello, SwiftUI!" and a button that changes the text to "Button tapped!" when pressed. Which code snippet correctly implements this behavior?

hard

A. struct ContentView: View {
@State private var message = "Hello, SwiftUI!"
var body: some View {
VStack {
Text("Hello, SwiftUI!")
Button("Tap") {
message = "Button tapped!"
}
}
}
}

B. struct ContentView: View {
var message = "Hello, SwiftUI!"
var body: some View {
VStack {
Text(message)
Button("Tap") {
message = "Button tapped!"
}
}
}
}

C. struct ContentView: View {
var message = "Hello, SwiftUI!"
var body: some View {
VStack {
Text(message)
Button { message = "Button tapped!" } label: { Text("Tap") }
}
}
}

D. struct ContentView: View {
@State private var message = "Hello, SwiftUI!"
var body: some View {
VStack {
Text(message)
Button("Tap") {
message = "Button tapped!"
}
}
}
}

Solution

1. Step 1: Use @State for mutable text

   The text changes when the button is tapped, so message must be a @State variable.

2. Step 2: Update text on button tap

   The button action updates message to "Button tapped!" and the UI reflects this change.

3. Step 3: Verify correct syntax

   struct ContentView: View { @State private var message = "Hello, SwiftUI!" var body: some View { VStack { Text(message) Button("Tap") { message = "Button tapped!" } } } } uses @State private var, a VStack with Text(message), and a button with label and action correctly.

4. Final Answer:

   A -> Option D

5. Quick Check:

   @State variable updates text on button tap [OK]

Hint: Use @State for text that changes on button tap [OK]

Common Mistakes:

• Not using @State for mutable text
• Using constant text in Text view
• Incorrect button label or action syntax