AnimationTestTableViewController.swift

// Demo for SO question:
//
// http://stackoverflow.com/questions/42659251/can-a-table-view-row-stay-put-while-its-section-is-moving

import UIKit

enum State: Int {
    case first
    case second
}

class TableViewController: UITableViewController {

    var state: State = .first
    
    override func viewDidLoad() {
        super.viewDidLoad()

        tableView.register(UITableViewCell.self, forCellReuseIdentifier: "cell")
        
        update()
    }

    // Hook up to a bar button item for testing
    @IBAction func cycle(_ sender: Any) {
        if let new = State(rawValue: state.rawValue + 1) {
            state = new
        } else {
            state = .first
        }
        update()
    }

    var sections: [(String, [String])] = []
    
    func update() {
        tableView.beginUpdates()
        
        // Pick on of these:
        switchItems()
//        switchSections()
//        switchBothNoOp()
//        switchBothCrash()
        
        tableView.endUpdates()
    }
    
    func switchItems() {
        switch state {
        case .first:
            sections = [("Fruits", ["Banana"]),
                        ("Vegetables", ["Carrot"])]
            
        case .second:
            sections = [("Fruits", ["Carrot"]),
                        ("Vegetables", ["Banana"])]
        }

        tableView.moveRow(at: [0, 0], to: [1, 0])
        tableView.moveRow(at: [1, 0], to: [0, 0])
}
    
    func switchSections() {
        switch state {
        case .first:
            sections = [("Fruits", ["Banana"]),
                        ("Vegetables", ["Carrot"])]
            
        case .second:
            sections = [("Vegetables", ["Carrot"]),
                        ("Fruits", ["Banana"])]
        }

        tableView.moveSection(0, toSection: 1)
    }
    
    func switchBothNoOp() {
        switch state {
        case .first:
            sections = [("Fruits", ["Banana"]),
                        ("Vegetables", ["Carrot"])]
            
        case .second:
            sections = [("Vegetables", ["Banana"]),
                        ("Fruits", ["Carrot"])]
        }

        tableView.moveSection(0, toSection: 1)
        tableView.moveSection(1, toSection: 0)
        tableView.moveRow(at: [0, 0], to: [0, 0])
        tableView.moveRow(at: [1, 0], to: [1, 0])
    }

    func switchBothCrash() {
        switch state {
        case .first:
            sections = [("Fruits", ["Banana"]),
                        ("Vegetables", ["Carrot"])]
            
        case .second:
            sections = [("Vegetables", ["Banana"]),
                        ("Fruits", ["Carrot"])]
        }

        tableView.moveSection(0, toSection: 1)
        tableView.moveSection(1, toSection: 0)
        tableView.deleteRows(at: [[0, 0], [1, 0]], with: .fade)
        tableView.insertRows(at: [[0, 0], [1, 0]], with: .fade)
    }
    
    // MARK: Data source
    
    override func numberOfSections(in tableView: UITableView) -> Int {
        return sections.count
    }
    
    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return sections[section].1.count
    }
    
    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath)
        cell.textLabel?.text = sections[indexPath.section].1[indexPath.row]
        return cell
    }
    
    override func tableView(_ tableView: UITableView, titleForHeaderInSection section: Int) -> String? {
        return sections[section].0
    }
}