Add defaultCellConfiguration for easy cell styling

- Add DefaultCellConfiguration typealias and property to DataTableConfiguration
- Make DataCell.dataLabel public for user access
- Add prepareForReuse to DataCell to reset styling on cell reuse
- Deprecate delegate colour methods (highlightedColorForRowIndex, unhighlightedColorForRowIndex)
- Add comprehensive tests for the new API
- Add Cell Styling demo with 5 interactive examples
- Update documentation with DefaultCellConfiguration guide
- Update README, Styling, CustomCells, and migration docs

Resolves #39 (change font) and #17 (change cell colour)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: pavankataria

Example/DemoSwiftDataTables/App/MenuTableViewController.swift

@@ -113,11 +113,12 @@ class MenuViewController: UITableViewController {
             ],
             // Section 6: Visual Styling
             [
+                MenuItem(title: "Cell Styling"),
                 MenuItem(title: "Sort Arrow Styling"),
                 MenuItem(
-                    title: "Alternating Row Colours",
+                    title: "Alternating Row Colours (Simple)",
                     config: configurationAlternatingColours(),
-                    description: "Custom rainbow alternating row colours. Set highlightedAlternatingRowColors and unhighlightedAlternatingRowColors."
+                    description: "Simple alternating row colours using highlightedAlternatingRowColors and unhighlightedAlternatingRowColors arrays. For more control (fonts, conditional styling), use defaultCellConfiguration instead - see Cell Styling demo."
                 ),
             ],
             // Section 7: Performance
@@ -273,8 +274,10 @@ extension MenuViewController {
     private func handleVisualStyling(row: Int) {
         switch row {
         case 0:
-            show(SortArrowStylingDemoViewController(), sender: self)
+            show(CellStylingDemoViewController(), sender: self)
         case 1:
+            show(SortArrowStylingDemoViewController(), sender: self)
+        case 2:
             let menuItem = menuItems[Section.visualStyling.rawValue][row]
             if let config = menuItem.config {
                 let instance = GenericDataTableViewController(

Example/DemoSwiftDataTables/Demos/CellStyling/CellStylingDemoViewController+Explanation.swift

@@ -0,0 +1,78 @@
+//
+//  CellStylingDemoViewController+Explanation.swift
+//  SwiftDataTables
+//
+//  Created by Pavan Kataria on 28/01/2026.
+//  Copyright © 2016-2026 Pavan Kataria. All rights reserved.
+//
+
+import UIKit
+
+extension CellStylingDemoViewController {
+
+    struct ExplanationControls {
+        let view: DemoExplanationView
+        let styleButtons: [UIButton]
+    }
+
+    func makeExplanationControls(styleOptions: [String]) -> ExplanationControls {
+        let styleButtons: [UIButton] = styleOptions.enumerated().map { index, title in
+            let button = UIButton(type: .system)
+            button.setTitle(title, for: .normal)
+            button.titleLabel?.font = .systemFont(ofSize: 12, weight: .medium)
+            button.titleLabel?.numberOfLines = 2
+            button.titleLabel?.textAlignment = .center
+            button.tag = index
+            button.addTarget(self, action: #selector(styleButtonTapped(_:)), for: .touchUpInside)
+            button.layer.cornerRadius = 8
+            button.layer.borderWidth = 1
+            button.layer.borderColor = UIColor.systemBlue.cgColor
+            button.contentEdgeInsets = UIEdgeInsets(top: 8, left: 8, bottom: 8, right: 8)
+            return button
+        }
+
+        let row1 = UIStackView(arrangedSubviews: Array(styleButtons[0..<3]))
+        row1.axis = .horizontal
+        row1.spacing = 8
+        row1.distribution = .fillEqually
+
+        let row2 = UIStackView(arrangedSubviews: Array(styleButtons[3..<5]))
+        row2.axis = .horizontal
+        row2.spacing = 8
+        row2.distribution = .fillEqually
+
+        let buttonStack = UIStackView(arrangedSubviews: [row1, row2])
+        buttonStack.axis = .vertical
+        buttonStack.spacing = 8
+
+        let codeLabel = UILabel()
+        codeLabel.font = .monospacedSystemFont(ofSize: 11, weight: .regular)
+        codeLabel.textColor = .secondaryLabel
+        codeLabel.numberOfLines = 0
+        codeLabel.text = """
+        config.defaultCellConfiguration = { cell, value, indexPath, isHighlighted in
+            cell.dataLabel.font = .custom
+            cell.dataLabel.textColor = .conditional
+            cell.backgroundColor = .alternating
+        }
+        """
+
+        let explanationView = DemoExplanationView(
+            description: """
+            Customise default cells without creating custom cell classes. \
+            Use defaultCellConfiguration to set font, text colour, background, \
+            and more based on value, position, or highlight state.
+
+            This replaces the deprecated delegate methods \
+            dataTable(_:highlightedColorForRowIndex:) and \
+            dataTable(_:unhighlightedColorForRowIndex:).
+            """,
+            controls: [buttonStack, codeLabel]
+        )
+
+        return ExplanationControls(
+            view: explanationView,
+            styleButtons: styleButtons
+        )
+    }
+}

Example/DemoSwiftDataTables/Demos/CellStyling/CellStylingDemoViewController.swift

@@ -0,0 +1,229 @@
+//
+//  CellStylingDemoViewController.swift
+//  SwiftDataTables
+//
+//  Created by Pavan Kataria on 28/01/2026.
+//  Copyright © 2016-2026 Pavan Kataria. All rights reserved.
+//
+
+import UIKit
+import SwiftDataTables
+
+final class CellStylingDemoViewController: UIViewController {
+
+    // MARK: - Data
+
+    let sampleData = samplePeople()
+
+    let columns: [DataTableColumn<SamplePerson>] = [
+        .init("ID", \.id),
+        .init("Name", \.name),
+        .init("Email", \.email),
+        .init("Number", \.phone),
+        .init("City", \.city),
+        .init("Balance", \.balance)
+    ]
+
+    // MARK: - State
+
+    private var selectedStyleIndex: Int = 0
+
+    let styleOptions: [String] = [
+        "Custom Font",
+        "Negative Values Red",
+        "Per-Column Styling",
+        "Alternating Colours",
+        "Combined Styling"
+    ]
+
+    // MARK: - UI
+
+    private var controls: ExplanationControls!
+    private var dataTable: SwiftDataTable?
+
+    // MARK: - Lifecycle
+
+    override func viewDidLoad() {
+        super.viewDidLoad()
+        title = "Cell Styling"
+        view.backgroundColor = .systemBackground
+
+        controls = makeExplanationControls(styleOptions: styleOptions)
+        installExplanation(controls.view)
+
+        updateButtonAppearance()
+        updateUI()
+        rebuildTable()
+    }
+
+    // MARK: - Actions
+
+    @objc func styleButtonTapped(_ sender: UIButton) {
+        selectedStyleIndex = sender.tag
+        updateButtonAppearance()
+        updateUI()
+        rebuildTable()
+    }
+
+    // MARK: - UI Updates
+
+    private func updateButtonAppearance() {
+        for (index, button) in controls.styleButtons.enumerated() {
+            let isSelected = index == selectedStyleIndex
+            button.backgroundColor = isSelected ? .systemBlue : .clear
+            button.setTitleColor(isSelected ? .white : .systemBlue, for: .normal)
+        }
+    }
+
+    private func updateUI() {
+        let descriptions = [
+            "Custom font applied to all cells using Avenir-Medium.",
+            "Balance column shows negative values in red, positive in green.",
+            "ID column uses monospaced digits, City column is centered.",
+            "Rainbow row colours cycling through 7 colours, with highlight for sorted column.",
+            "All styling combined: font, conditional colours, and row striping."
+        ]
+        controls.view.updateSummary(descriptions[selectedStyleIndex])
+    }
+
+    private func rebuildTable() {
+        dataTable?.removeFromSuperview()
+
+        var config = DataTableConfiguration()
+        config.defaultOrdering = DataTableColumnOrder(index: 5, order: .descending) // Sort by Balance
+
+        // Apply the selected styling
+        switch selectedStyleIndex {
+        case 0:
+            config.defaultCellConfiguration = customFontConfiguration()
+        case 1:
+            config.defaultCellConfiguration = negativeValuesConfiguration()
+        case 2:
+            config.defaultCellConfiguration = perColumnConfiguration()
+        case 3:
+            config.defaultCellConfiguration = alternatingColoursConfiguration()
+        case 4:
+            config.defaultCellConfiguration = combinedConfiguration()
+        default:
+            break
+        }
+
+        let table = SwiftDataTable(data: sampleData, columns: columns, options: config)
+        table.backgroundColor = UIColor(red: 235/255, green: 235/255, blue: 235/255, alpha: 1)
+
+        addDataTable(table, below: controls.view)
+        dataTable = table
+    }
+
+    // MARK: - Cell Configuration Styles
+
+    private func customFontConfiguration() -> DefaultCellConfiguration {
+        return { cell, _, _, _ in
+            cell.dataLabel.font = UIFont(name: "Avenir-Medium", size: 14)
+        }
+    }
+
+    private func negativeValuesConfiguration() -> DefaultCellConfiguration {
+        return { cell, value, indexPath, _ in
+            // Only apply colour logic to Balance column (index 5)
+            if indexPath.section == 5 {
+                let balance = value.stringRepresentation
+                    .replacingOccurrences(of: "£", with: "")
+                    .replacingOccurrences(of: ",", with: "")
+                if let number = Double(balance) {
+                    if number < 0 {
+                        cell.dataLabel.textColor = .systemRed
+                        cell.dataLabel.font = .boldSystemFont(ofSize: 14)
+                    } else {
+                        cell.dataLabel.textColor = .systemGreen
+                        cell.dataLabel.font = .systemFont(ofSize: 14)
+                    }
+                }
+            } else {
+                cell.dataLabel.textColor = .label
+                cell.dataLabel.font = .systemFont(ofSize: 14)
+            }
+        }
+    }
+
+    private func perColumnConfiguration() -> DefaultCellConfiguration {
+        return { cell, _, indexPath, _ in
+            switch indexPath.section {
+            case 0: // ID column - monospaced
+                cell.dataLabel.font = .monospacedDigitSystemFont(ofSize: 13, weight: .regular)
+                cell.dataLabel.textColor = .secondaryLabel
+            case 4: // City column - centered
+                cell.dataLabel.font = .systemFont(ofSize: 14, weight: .medium)
+                cell.dataLabel.textAlignment = .center
+            case 5: // Balance column - right aligned
+                cell.dataLabel.font = .monospacedDigitSystemFont(ofSize: 14, weight: .semibold)
+                cell.dataLabel.textAlignment = .right
+            default:
+                cell.dataLabel.font = .systemFont(ofSize: 14)
+                cell.dataLabel.textAlignment = .natural
+                cell.dataLabel.textColor = .label
+            }
+        }
+    }
+
+    private func alternatingColoursConfiguration() -> DefaultCellConfiguration {
+        return { cell, _, indexPath, isHighlighted in
+            // Rainbow colours like the classic demo
+            let highlightedColours: [UIColor] = [
+                UIColor(red: 1, green: 0.7, blue: 0.7, alpha: 1),
+                UIColor(red: 1, green: 0.7, blue: 0.5, alpha: 1),
+                UIColor(red: 1, green: 1, blue: 0.5, alpha: 1),
+                UIColor(red: 0.5, green: 1, blue: 0.5, alpha: 1),
+                UIColor(red: 0.5, green: 0.7, blue: 1, alpha: 1),
+                UIColor(red: 0.5, green: 0.5, blue: 1, alpha: 1),
+                UIColor(red: 1, green: 0.5, blue: 0.5, alpha: 1)
+            ]
+            let unhighlightedColours: [UIColor] = [
+                UIColor(red: 1, green: 0.90, blue: 0.90, alpha: 1),
+                UIColor(red: 1, green: 0.90, blue: 0.7, alpha: 1),
+                UIColor(red: 1, green: 1, blue: 0.7, alpha: 1),
+                UIColor(red: 0.7, green: 1, blue: 0.7, alpha: 1),
+                UIColor(red: 0.7, green: 0.9, blue: 1, alpha: 1),
+                UIColor(red: 0.7, green: 0.7, blue: 1, alpha: 1),
+                UIColor(red: 1, green: 0.7, blue: 0.7, alpha: 1)
+            ]
+
+            let colours = isHighlighted ? highlightedColours : unhighlightedColours
+            cell.backgroundColor = colours[indexPath.item % colours.count]
+        }
+    }
+
+    private func combinedConfiguration() -> DefaultCellConfiguration {
+        return { cell, value, indexPath, isHighlighted in
+            // 1. Alternating row colours
+            let highlightedColours: [UIColor] = [
+                .systemBlue.withAlphaComponent(0.08),
+                .systemBlue.withAlphaComponent(0.12)
+            ]
+            let unhighlightedColours: [UIColor] = [
+                .systemBackground,
+                .secondarySystemBackground
+            ]
+            let colours = isHighlighted ? highlightedColours : unhighlightedColours
+            cell.backgroundColor = colours[indexPath.item % colours.count]
+
+            // 2. Per-column styling
+            switch indexPath.section {
+            case 0: // ID
+                cell.dataLabel.font = .monospacedDigitSystemFont(ofSize: 12, weight: .regular)
+                cell.dataLabel.textColor = .tertiaryLabel
+            case 5: // Balance - conditional colouring
+                cell.dataLabel.font = .monospacedDigitSystemFont(ofSize: 14, weight: .semibold)
+                let balance = value.stringRepresentation
+                    .replacingOccurrences(of: "£", with: "")
+                    .replacingOccurrences(of: ",", with: "")
+                if let number = Double(balance) {
+                    cell.dataLabel.textColor = number < 0 ? .systemRed : .systemGreen
+                }
+            default:
+                cell.dataLabel.font = UIFont(name: "Avenir-Medium", size: 14)
+                cell.dataLabel.textColor = .label
+            }
+        }
+    }
+}