📱 Working with UITableView Data Source and Delegate (iOS – Xcode)

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✅ 1. Definition

🔹 UITableView Data Source

The Data Source is responsible for providing data to the table view. It tells the table view:

• How many rows to display
• What content each row (cell) should show

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🔹 UITableView Delegate

The Delegate handles user interactions and appearance behavior of the table view. It controls:

• Row selection
• Row height
• Editing actions

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👉 Simple idea:

• Data Source = gives data
• Delegate = controls behavior

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🧠 2. Key Concepts

🔹 UITableView Protocols

To use a table view, your ViewController must conform to:

UITableViewDataSource
UITableViewDelegate

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🔹 IndexPath

• Represents the position of a cell

• Contains:

  • section
  • row

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🏗️ 3. Structure of Table View System

UITableView
   ↓
DataSource → provides data
Delegate   → handles interaction
   ↓
UITableViewCell (rows)

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⚙️ 4. Step-by-Step Implementation

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🔹 Step 1: Connect Table View

@IBOutlet weak var tableView: UITableView!

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🔹 Step 2: Set Delegate and Data Source

override func viewDidLoad() {
    super.viewDidLoad()
    
    tableView.dataSource = self
    tableView.delegate = self
}

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🔹 Step 3: Create Data Array

let fruits = ["Apple", "Banana", "Mango", "Orange"]

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📦 5. Data Source Methods

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🔹 1. Number of Rows

func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return fruits.count
}

👉 Tells how many rows to display

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🔹 2. Cell for Row

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

    let cell = UITableViewCell(style: .default, reuseIdentifier: "cell")
    cell.textLabel?.text = fruits[indexPath.row]
    return cell
}

👉 Creates and configures each cell

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🎯 6. Delegate Methods

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🔹 1. Row Selection

func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
    print("Selected: \(fruits[indexPath.row])")
}

👉 Called when user taps a row

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🔹 2. Row Height

func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
    return 60
}

👉 Controls row size

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🔹 3. Deselect Row (Good Practice)

func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
    tableView.deselectRow(at: indexPath, animated: true)
}

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📊 7. Diagram Description (for Exams)

Draw:

UITableView
   ↓
DataSource → rows + content
Delegate   → tap + behavior
   ↓
Cells (UITableViewCell)

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💡 8. Example App

🎯 Fruits List App

let fruits = ["Apple", "Banana", "Mango"]

func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return fruits.count
}

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell = UITableViewCell()
    cell.textLabel?.text = fruits[indexPath.row]
    return cell
}

func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
    print("You selected \(fruits[indexPath.row])")
}

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📌 9. Important Rules / Tips

• Always set dataSource and delegate
• Data source handles data only
• Delegate handles user actions
• Use IndexPath.row to access array data
• Always reload table after data changes:

tableView.reloadData()

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⚠️ 10. Common Mistakes

• ❌ Forgetting to set delegate/dataSource
• ❌ Wrong index usage
• ❌ Not reloading table after updating data
• ❌ Returning wrong number of rows
• ❌ Crashing due to out-of-range index

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🧠 11. Best Practices

• Use arrays or models for data
• Separate UI logic from data logic
• Use custom cells for complex UI
• Always handle selection properly
• Keep delegate methods lightweight

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📝 12. Likely Exam Questions

1. What is UITableViewDataSource?
2. What is UITableViewDelegate?
3. Differentiate between data source and delegate.
4. Explain cellForRowAt method.
5. What is IndexPath used for?
6. Write code for table view setup.
7. Explain didSelectRowAt method.
8. Why is reloadData() used?

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📚 13. Quick Revision Summary

• Data Source → provides data (rows + content)

• Delegate → handles user interaction

• Key methods:

  • numberOfRowsInSection
  • cellForRowAt
  • didSelectRowAt

• Uses IndexPath to access data

• reloadData() updates table view

• Essential for all list-based apps

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