📱 Using View Controllers: Working with the Single View Template (iOS – Xcode)

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✅ 1. Definition

A View Controller is a core component in iOS that manages a screen (view) and handles its behavior, logic, and user interactions.

The Single View Template in Xcode is the simplest app template, providing one main screen controlled by a single view controller.

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🧠 2. Key Concepts

🔹 View Controller

• A class (usually UIViewController) that:

  • Controls UI elements
  • Responds to user actions
  • Manages data

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🔹 Single View App

• Default template when creating a new project

• Contains:

  • One screen
  • One view controller (ViewController.swift)

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🔹 Lifecycle of a View Controller

Method	Purpose
viewDidLoad()	Called when view loads into memory
viewWillAppear()	Before view appears
viewDidAppear()	After view appears
viewWillDisappear()	Before view disappears

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🏗️ 3. Structure of Single View Template

When you create a project, you get:

• AppDelegate.swift → App lifecycle
• SceneDelegate.swift → Scene management
• ViewController.swift → Main screen logic
• Main.storyboard → UI design

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📊 Diagram Description (for Exams)

Draw:

App → ViewController → View → UI Elements (Label, Button)

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⚙️ 4. Steps to Work with Single View Template

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🔹 Step 1: Create Project

• Open Xcode
• Select App (iOS)
• Choose Single View App

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🔹 Step 2: Understand Default Files

ViewController.swift

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Code here
    }
}

👉 viewDidLoad() is where initial setup is done

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🔹 Step 3: Design UI

• Open Main.storyboard

• Drag:

  • Label
  • Button

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🔹 Step 4: Connect UI to Code

@IBOutlet weak var label: UILabel!

@IBAction func buttonTapped(_ sender: UIButton) {
    label.text = "Hello iOS!"
}

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🔹 Step 5: Run the App

• Select Simulator
• Click Run ▶️

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🧩 5. Working with View Controller Code

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🔹 Example: Changing Background Color

override func viewDidLoad() {
    super.viewDidLoad()
    view.backgroundColor = .lightGray
}

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🔹 Example: Show Message on Load

override func viewDidLoad() {
    super.viewDidLoad()
    print("View Loaded")
}

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📌 6. Important Rules / Tips

• Always write setup code inside viewDidLoad()
• Keep UI logic inside View Controller
• Avoid putting too much code in one controller
• Use meaningful names for outlets/actions
• Test frequently

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💡 7. Example Application

🎯 Simple Greeting App

UI:

• TextField → Enter name
• Button → Submit
• Label → Display message

Code:

@IBOutlet weak var nameField: UITextField!
@IBOutlet weak var messageLabel: UILabel!

@IBAction func showGreeting(_ sender: UIButton) {
    messageLabel.text = "Hello \(nameField.text ?? "")"
}

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⚠️ 8. Common Mistakes

• ❌ Forgetting to connect outlets
• ❌ Writing code outside lifecycle methods
• ❌ Not updating UI on main thread
• ❌ Overloading ViewController with too much logic

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📝 9. Likely Exam Questions

1. Define View Controller in iOS.
2. What is the Single View Template?
3. Explain the lifecycle of a view controller.
4. What is the role of viewDidLoad()?
5. Describe the structure of a Single View App.
6. How do you connect UI elements to ViewController?
7. Write code to change label text on button click.
8. Draw a diagram showing ViewController relationship.

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📚 10. Quick Revision Summary

• View Controller manages one screen

• Single View Template = one screen app

• Main file: ViewController.swift

• UI designed in Storyboard

• Use:

  • IBOutlet → connect UI
  • IBAction → handle actions

• Important method:

  • viewDidLoad() → initial setup

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