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iOS is a mobile operating system developed by Apple for its devices like iPhone, iPad, and iPod Touch. It is known for high performance, strong security, and a smooth user experience.
Apple controls both hardware and software, which makes iOS apps more optimized compared to other platforms. iOS supports features like touch gestures, Face ID, push notifications, and App Store distribution.
For beginners, understanding iOS means learning how apps are built, how users interact with them, and how Apple’s ecosystem works.
Xcode is Apple’s official development tool used to create iOS applications. It is an Integrated Development Environment (IDE) that provides everything needed to build apps.
With Xcode, developers can:
It also includes Interface Builder, which helps you design app screens visually without writing too much code.
There are mainly two programming languages used in iOS development:
Swift:
Swift is the modern language developed by Apple. It is easy to read, fast, and safe. Most new iOS apps are built using Swift.
Objective-C:
Objective-C is an older language used before Swift. Many old apps still use it, so sometimes developers need to understand it for maintenance.
Example of Swift code:
print("Hello, iOS World!")
For beginners, Swift is the best choice because it is simple and powerful.
Swift is a programming language created by Apple in 2014. It is used for building iOS, macOS, watchOS, and tvOS applications.
Key features of Swift:
Example:
var name = "Rajan"
print("Hello \(name)")
Swift is beginner-friendly and widely used in the industry, so it is important for interviews.
UIKit is a framework used to design and manage the user interface in iOS apps. It provides ready-made UI components.
Some common UIKit components:
UIKit follows an event-driven approach, where user actions like tapping or scrolling trigger events.
Example:
let label = UILabel()
label.text = "Welcome to iOS"
Even though SwiftUI is growing, UIKit is still widely used in many projects.
SwiftUI is a modern framework introduced by Apple to build UI in a simple and faster way using declarative syntax.
Instead of telling the system how to create UI step-by-step, you tell what you want.
Example:
Text("Hello, World!")
.font(.title)
.color(.blue)
Advantages of SwiftUI:
SwiftUI is becoming very popular, especially for new apps.
MVC stands for Model-View-Controller. It is a design pattern used to organize code in iOS apps.
Model:
Handles data and business logic.
View:
Displays UI elements to the user.
Controller:
Acts as a bridge between Model and View. It controls user interaction and updates UI.
Example:
Model → User data
View → Profile screen
Controller → Manages data and updates screen
MVC helps keep code clean and organized, which is important in large applications.
These are used to connect UI elements with code in Storyboard.
IBOutlet:
Used to connect UI elements (like buttons, labels) to code so you can modify them.
Example:
@IBOutlet weak var label: UILabel!
IBAction:
Used to handle user actions like button clicks.
Example:
@IBAction func buttonClicked(_ sender: UIButton) {
print("Button Pressed")
}
These connections are created using Interface Builder in Xcode.
Storyboard is a visual design tool in Xcode used to create app UI and navigation.
Features:
However, in modern development, many developers prefer SwiftUI or programmatic UI for better control.
Auto Layout is used to make your app UI responsive for different screen sizes and orientations.
Instead of setting fixed positions, you define constraints like:
Auto Layout ensures your app looks good on all devices like iPhone SE, iPhone 15, etc.
Delegation is a design pattern used in iOS to pass data or events from one object to another.
In simple words, one object gives responsibility to another object to handle some task.
For example:
Example:
protocol MyDelegate {
func didPerformAction()
}
Delegation helps in:
A protocol is like a blueprint that defines methods, properties, or requirements that a class, struct, or enum must follow.
It does not contain implementation, only rules.
Example:
protocol Animal {
func makeSound()
}
Any class that adopts this protocol must implement the method.
class Dog: Animal {
func makeSound() {
print("Bark")
}
}
Protocols are very important in iOS interviews because they are widely used with delegation and abstraction.
A closure is a block of code that can be passed around and executed later.
It is similar to functions but more flexible.
Example:
let greet = {
print("Hello World")
}
greet()
Closures are used in:
Example with parameter:
let add = { (a: Int, b: Int) -> Int in
return a + b
}
Closures make code shorter and more powerful.
An optional is a variable that can either have a value or be nil (no value).
It helps avoid crashes due to missing values.
Example:
var name: String? = "Rajan"
To use optional safely:
Optional Binding
if let name = name {
print(name)
}
Force Unwrapping (not recommended)
print(name!)
Optionals are very important in Swift because they ensure safe coding.
Struct and Class are used to create data models, but they behave differently.
Struct:
Class:
Example:
struct Person {
var name: String
}
class Car {
var model: String = ""
}
In interviews, remember:
👉 Struct = lightweight
👉 Class = powerful and flexible
ARC is a memory management system in iOS that automatically frees unused memory.
It keeps track of how many references are pointing to an object.
When no references are left → memory is released.
Example:
class Person {
var name: String
init(name: String) {
self.name = name
}
}
ARC helps:
ViewController is a core component in iOS apps that manages a single screen.
It handles:
Example:
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
}
}
Each screen in an app usually has its own ViewController.
A Navigation Controller is used to manage multiple screens in a stack format.
It allows:
Example:
TableView is used to display a list of data in rows.
Example:
Example:
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return 10
}
TableView is one of the most commonly used components in iOS apps.
CollectionView is similar to TableView but more flexible.
It is used for grid layouts and custom designs.
Example:
Example:
let layout = UICollectionViewFlowLayout()
let collectionView = UICollectionView(frame: .zero, collectionViewLayout: layout)
CollectionView is used when you need advanced UI layouts.
The App Lifecycle defines the different states an iOS app goes through during its execution.
Main states:
These states are managed by:
Understanding lifecycle helps manage app behavior like saving data or stopping tasks.
AppDelegate is a class that handles important app-level events.
It manages:
Example:
func application(
_ application: UIApplication,
didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
) -> Bool {
return true
}
It acts as the entry point of the app.
SceneDelegate was introduced in iOS 13 to manage multiple UI scenes (windows).
It handles:
Difference:
This improves multitasking and multiple window support.
UserDefaults is used to store small amounts of data locally in key-value format.
Used for:
Example:
UserDefaults.standard.set("Rajan", forKey: "username")
To retrieve:
let name = UserDefaults.standard.string(forKey: "username")
It is simple but not suitable for large or sensitive data.
Core Data is a framework used for storing and managing large amounts of structured data locally.
It works like a local database.
Features:
Core Data is more powerful than UserDefaults.
API (Application Programming Interface) allows apps to communicate with servers.
It is used to:
Most APIs use JSON format for data exchange.
JSON (JavaScript Object Notation) is a lightweight data format used for sending and receiving data from APIs.
Example:
{
"name": "Rajan",
"age": 22
}
In iOS, JSON is converted into Swift objects using Codable.
Example:
struct User: Codable {
let name: String
let age: Int
}
URLSession is used to make network requests in iOS.
It helps:
Example:
let url = URL(string: "https://api.example.com")!
let task = URLSession.shared.dataTask(with: url) { data, response, error in
if let data = data {
print(data)
}
}
task.resume()
It is a core concept for API integration.
GCD is used for managing multiple tasks and performing operations in the background.
It helps:
Example:
DispatchQueue.global().async {
print("Background task")
}
Main queue:
DispatchQueue.main.async {
print("Update UI")
}
GCD is very important for smooth user experience.
Multithreading means running multiple tasks at the same time.
In iOS:
Cocoa Touch is the main framework used for building iOS applications. It provides essential tools and APIs to handle user interaction, UI elements, and app behavior.
It includes frameworks like:
Cocoa Touch helps developers create interactive and responsive apps easily.
Foundation is a core framework in iOS that provides basic functionalities needed for app development.
It includes:
Example:
let array = [1, 2, 3]
Foundation works behind the scenes in almost every iOS app.
Core Animation is used to add animations to iOS apps.
It helps create:
Animations improve user experience and make apps more interactive.
Push notifications are messages sent from a server to a user’s device.
They are used for:
Push notifications use Apple Push Notification Service (APNs).
Local notifications are created and scheduled within the app itself.
Difference:
They work even without internet.
Core Location is a framework used to get the user’s location.
It provides:
It requires user permission for privacy.
MapKit is used to display maps in iOS apps.
Features:
Gesture Recognizer is used to detect user interactions like touch gestures.
Types of gestures:
Example:
let tap = UITapGestureRecognizer(target: self, action: #selector(handleTap))
view.addGestureRecognizer(tap)
It helps create interactive apps.
Keychain is used to securely store sensitive data.
It is used for:
Sandbox is a security feature in iOS that restricts app access.
Each app has its own isolated environment where it can:
MVVM stands for Model-View-ViewModel. It is an advanced architecture pattern used in iOS apps to make code more organized and scalable.
Model:
Handles data and business logic.
View:
Displays UI to the user.
ViewModel:
Acts as a bridge between Model and View. It prepares data for the UI.
Difference from MVC:
MVC → Controller becomes very heavy
MVVM → Better separation, cleaner code
MVVM is commonly used with SwiftUI and modern iOS apps.
Dependency Injection is a technique where objects receive their dependencies from outside instead of creating them internally.
Example:
Instead of:
let api = APIService()
Use:
init(apiService: APIService) {
self.apiService = apiService
}
Benefits:
This concept is important in large-scale apps.
Singleton ensures that only one instance of a class is created and shared across the app.
Example:
class Manager {
static let shared = Manager()
private init() {}
}
Usage:
A lazy property is initialized only when it is used for the first time.
Example:
lazy var data = loadData()
Benefits:
Lazy properties are helpful when data loading is expensive.
A computed property does not store a value but calculates it when accessed.
Example:
var fullName: String {
return firstName + " " + lastName
}
It is useful when:
Value depends on other variables
You don’t want to store duplicate data
Error handling is used to manage runtime errors safely.
Swift uses:
Example:
do {
try someFunction()
} catch {
print("Error occurred")
}
It prevents app crashes and improves stability.
Codable is used to convert data between JSON and Swift objects.
Example:
struct User: Codable {
let name: String
}
Decode JSON:
let user = try JSONDecoder().decode(User.self, from: data)
Encode JSON:
let json = try JSONEncoder().encode(user)
Codable makes API handling very easy.
Dark Mode is a UI feature that changes app appearance to a dark theme.
Benefits:
Example:
label.textColor = .label
TestFlight is Apple’s platform used for testing iOS apps before release.
Features:
It helps find bugs before final release.
App deployment is the process of publishing an app on the Apple App Store.
Steps:
Requirements:
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