Expandable UITableView

1) ExpandableTableView.swift

import UIKit

class ExpandableObject {
    
    public var subItems = [ExpandableObject]()
    public var title: String?
    public var isExpanded: Bool = false
    public var isChild: Bool = false
    public var cellIdentifier: String?
    public var canExpand: Bool {
        return self.subItems.count > 0
    }
    
    init(_ title: String?, isChild: Bool = false) {
        self.title = title
        self.isChild = isChild
    }
    
    init(cellIdentifier: String?, isChild: Bool = false) {
        self.cellIdentifier = cellIdentifier
        self.isChild = isChild
    }
}

protocol ExpandableCell {
    func canExpandCell() -> Bool
    func isCellExpanded() -> Bool
    func setCellIsExpanded(expanded: Bool)
    func numberOfExpandableElements() -> Int
}

protocol ExpandableTableViewDataSource {
    func expand(_ tableView: ExpandableTableView, at indexPath: IndexPath, expand: Bool)
    func isCellExpanded(_ tableView: ExpandableTableView, at indexPath: IndexPath) -> Bool
    func expandableTableView(_ tableView: ExpandableTableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell
    func expandableTableView(_ tableView: ExpandableTableView, heightForRowAt indexPath: IndexPath) -> CGFloat
    func expandableTableView(_ tableView: ExpandableTableView, didSelectRowAt indexPath: IndexPath)
}

protocol ExpandableTableViewDelegate {
    func scrollViewDidScroll(_ scrollView: UIScrollView)
}

class ExpandableTableView: UITableView, UITableViewDataSource, UITableViewDelegate {

    public var customDataSource: ExpandableTableViewDataSource?
    public var customDelegate: ExpandableTableViewDelegate?
    
    public var expandableData = Dictionary<Int, [String?]>()
    
    internal var cellsData = [ExpandableObject]()
    
    internal var mappedCellsData: [ExpandableObject] {
        get {
            var newArray = [ExpandableObject]()
            for obj in self.cellsData {
                newArray.append(obj)
                if obj.isExpanded {
                    for subItem in obj.subItems {
                        newArray.append(subItem)
                        if subItem.isExpanded {
                            newArray.append(contentsOf: subItem.subItems)
                        }
                    }
                }
            }
            return newArray
        }
    }
    
    override init(frame: CGRect, style: UITableViewStyle) {
        super.init(frame: frame, style: style)
        self.setup()
    }
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        self.setup()
    }
    
    private func setup() {
        self.dataSource = self
        self.delegate = self
        self.estimatedRowHeight = 44.0
        self.backgroundColor = .clear
    }
    
    public func setCellsData(_ data: [ExpandableObject]) {
        self.cellsData = data
    }
    
    public func registerCell(with name: String) {
        self.register(UINib(nibName: String(describing: name), bundle: nil), forCellReuseIdentifier: String(describing: name))
    }
    
    public func object(at indexPath: IndexPath) -> ExpandableObject {
        return self.mappedCellsData[indexPath.row]
    }
    
    public func isLast(_ indexPath: IndexPath) -> Bool {
        return indexPath.row == self.mappedCellsData.count - 1
    }
    
    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return self.mappedCellsData.count
    }
    
    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        guard let ds = self.customDataSource else {
            return UITableViewCell()
        }
        return ds.expandableTableView(self, cellForRowAt:indexPath)
    }
    
    func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
        if let cell = tableView.cellForRow(at: indexPath) as? ExpandableCell {
            guard let ds = self.customDataSource else {
                return
            }
            if cell.canExpandCell() {
                ds.expand(self, at: indexPath, expand: !cell.isCellExpanded())
                self.reloadData()
            } else {
                ds.expandableTableView(self, didSelectRowAt: indexPath)
            }
        }
    }
    
    func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
        guard let ds = self.customDataSource else {
            return self.estimatedRowHeight
        }
        return ds.expandableTableView(self, heightForRowAt:indexPath)
    }
    
    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        self.customDelegate?.scrollViewDidScroll(scrollView)
    }
}

2) ExpandableTVC.swift

import UIKit

class ExpandableTVC: UITableViewCell, ExpandableCell {
    
    @IBOutlet weak var cellTitleLabel: UILabel!
    @IBOutlet weak var expandableImage: UIImageView!
    
    private var cellObject: ExpandableObject?
    
    override func awakeFromNib() {
        super.awakeFromNib()
    }

    override func setSelected(_ selected: Bool, animated: Bool) {
        super.setSelected(selected, animated: animated)
    }
    
    func setup(for object: ExpandableObject) {
        self.cellObject = object
        self.cellTitleLabel.text = self.cellObject?.title
        UIView.animate(withDuration: 0.15) {
            self.expandableImage.isHighlighted = (self.cellObject?.isExpanded ?? false)
        }
    }
    
    func canExpandCell() -> Bool {
        return self.cellObject?.canExpand ?? false
    }
    
    func isCellExpanded() -> Bool {
        return self.cellObject?.isExpanded ?? false
    }
    
    func setCellIsExpanded(expanded: Bool) {
        
    }
    
    func numberOfExpandableElements() -> Int {
        return self.cellObject?.subItems.count ?? 0
    }
}

3) AnyTableCell.swift

class AnyTableCell: UITableViewCell, ExpandableCell {
    
    override func awakeFromNib() {
        super.awakeFromNib()
    }
    
    override func setSelected(_ selected: Bool, animated: Bool) {
        super.setSelected(selected, animated: animated)
    }
    
    func setup() {

    }
    
    func canExpandCell() -> Bool {
        return false
    }
    
    func isCellExpanded() -> Bool {
        return false
    }
    
    func setCellIsExpanded(expanded: Bool) {
        
    }
    
    func numberOfExpandableElements() -> Int {
        return 0 // or if you setup cell with object: return self.cellObject?.subItems.count ?? 0
    }
}

4) Initialisation in View Contorller

func setupTableView() {
    self.tableView.customDataSource = self
    self.tableView.customDelegate = self
    self.tableView.estimatedRowHeight = 0
    self.tableView.registerCell(with: String(describing: ExpandableTVC.self)) // base cell
}

func setupCellsData() {
      var cellsData = [ExpandableObject]()
 
      // obj1 is expandable cell with 1 not expandable child cell
      let obj1 = ExpandableObject(cellIdentifier: String(describing: ExpandableTVC.self))
      obj1.title = "title1"
      obj1.subItems.append(ExpandableObject(cellIdentifier: String(describing: AnyTVC.self), isChild: true))
      cellsData.append(obj1)
      
      // obj1 is not expandable cell (no childs)
      let obj2 = ExpandableObject(cellIdentifier: String(describing: ExpandableTVC.self))
      obj2.title = "title2"
      cellsData.append(obj2)
      
      // obj1 is expandable cell with 2 childs
      let obj3 = ExpandableObject(cellIdentifier: String(describing: ExpandableTVC.self))
      obj3.title = "title3"
      obj3.subItems.append(ExpandableObject(cellIdentifier: String(describing: AnyTVC.self), isChild: true))
      obj3.subItems.append(ExpandableObject(cellIdentifier: String(describing: AnyTVC.self), isChild: true))
      cellsData.append(obj3)

      self.tableView.setCellsData(cellsData)
}

// MARK: - Expandable Table

// for cell which are not expandable
func expandableTableView(_ tableView: ExpandableTableView, didSelectRowAt indexPath: IndexPath) {

}

// for cell which are expandable
func expand(_ tableView: ExpandableTableView, at indexPath: IndexPath, expand: Bool) {
    let obj = tableView.object(at: indexPath)
    obj.isExpanded = expand

    let newCellIndexPath = IndexPath(row: indexPath.row + 1, section: 0)

    if expand {
        self.tableView.insertRows(at: [newCellIndexPath], with: .none)
    } else {
        self.tableView.deleteRows(at: [newCellIndexPath], with: .none)
    }

    self.tableView.beginUpdates()
    self.tableView.endUpdates()

    // or use this line instead of lines above
    //self.tableView.reloadData()
    self.tableView.scrollToRow(at: indexPath, at: .top, animated: false)
}

func isCellExpanded(_ tableView: ExpandableTableView, at indexPath: IndexPath) -> Bool {
    let obj = tableView.object(at: indexPath)
    return obj.isExpanded
}


 func expandableTableView(_ tableView: ExpandableTableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let obj = tableView.object(at: indexPath)
        guard let cellId = obj.cellIdentifier else {
            return UITableViewCell()
        }
        if cellId == String(describing: ExpandableTVC.self) {
        guard let cell = tableView.dequeueReusableCell(withIdentifier: cellId, for: indexPath) as? ExpandableTVC else {
            return UITableViewCell()
        }
        cell.setup(for: obj)
        return cell
    }
    if cellId == String(describing: SubDetailsTableCell.self) {
        guard let cell = tableView.dequeueReusableCell(withIdentifier: cellId, for: indexPath) as? SubDetailsTableCell else {
            return UITableViewCell()
        }
        cell.setup(...)
        return cell
    }
    return UITableViewCell()
}

func expandableTableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
    // if you need data from object: let obj = tableView.object(at: indexPath)
    return 50.0
}

// from delegate

func scrollViewDidScroll(_ scrollView: UIScrollView) {
   // ...
}