Building a Simple Stopwatch App in Swift: A Beginner’s Tutorial

Want to build your first iOS app? Follow this beginner-friendly tutorial to create a functional stopwatch app using Swift and UIKit. Perfect for learning basic iOS development concepts.

Introduction

A stopwatch app is an excellent first project for learning iOS development. It covers fundamental concepts like:

• UI design with UIKit
• Timer implementation
• Basic Swift programming
• User interaction handling

Prerequisites

Before starting this tutorial, make sure you have:

• Xcode installed
• Basic understanding of Swift syntax
• iOS development environment set up

Project Setup

1. Create a new Xcode project
2. Choose Single View Application
3. Set language to Swift
4. Name it “SimpleStopwatch”

Building the User Interface

Let’s create a clean, functional interface:

class ViewController: UIViewController {
    @IBOutlet weak var timeLabel: UILabel!
    @IBOutlet weak var startStopButton: UIButton!
    @IBOutlet weak var resetButton: UIButton!
    
    // Timer properties
    var timer: Timer?
    var elapsedTime: TimeInterval = 0
    var isRunning = false
}

Timer Implementation

Here’s how we implement the core stopwatch functionality:

extension ViewController {
    @objc func updateTimer() {
        elapsedTime += 0.1
        timeLabel.text = String(format: "%.1f", elapsedTime)
    }
    
    @IBAction func startStopTapped(_ sender: UIButton) {
        if isRunning {
            stopTimer()
        } else {
            startTimer()
        }
        isRunning = !isRunning
        startStopButton.setTitle(isRunning ? "Stop" : "Start", for: .normal)
    }
}

Adding Reset Functionality

@IBAction func resetTapped(_ sender: UIButton) {
    stopTimer()
    elapsedTime = 0
    timeLabel.text = "0.0"
    isRunning = false
    startStopButton.setTitle("Start", for: .normal)
}

Best Practices

1. Memory Management
   • Invalidate timer when view disappears
   • Clean up resources properly
2. User Interface
   • Use clear, readable fonts
   • Implement proper constraints
   • Add visual feedback
3. Code Organization
   • Separate concerns
   • Use meaningful variable names
   • Add proper comments

Common Issues and Solutions

Timer Accuracy

To improve timer accuracy:

timer = Timer(timeInterval: 0.1, 
             target: self,
             selector: #selector(updateTimer),
             userInfo: nil,
             repeats: true)
RunLoop.current.add(timer!, forMode: .common)

State Management

Properly handle app state changes:

override func viewWillDisappear(_ animated: Bool) {
    super.viewWillDisappear(animated)
    stopTimer()
}

Testing

Test your app thoroughly:

1. Start/Stop functionality
2. Reset button
3. Timer accuracy
4. State preservation
5. Memory usage

Next Steps

Consider adding these enhancements:

1. Lap times
2. Different time formats
3. Background running
4. Custom themes
5. Sound effects

Resources

• Apple’s Timer Documentation
• Swift Programming Guide
• UIKit Documentation

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This tutorial is part of our iOS Development series. Check out our other Swift tutorials for more learning resources.