Enlarging a cell in UITableView on long press using autolayout and UITableViewAutomaticDimension

EnlargingCellsOnLongPressAutolayoutController.swift

//
//  EnlargingCellsOnLongPressAutolayoutController.swift
//  EnlargingCellsExample
//
//  Created by Milan Nosáľ on 14/02/2018.
//  Copyright © 2018 Milan Nosáľ. All rights reserved.
//

import UIKit

class EnlargingCellsOnLongPressAutolayoutController: UITableViewController {
    // this will hold the cell we are currently enlarging
    var enlargingCell: EnlargingCell?
    // dummy data model
    var modelItems: [String] = []
    
    // some height limit, I will set it for myself to 200
    let limitHeight = CGFloat(200)
    
    // the enlarging itself will be done by a timer
    weak var timer: Timer?
    
    override func viewDidLoad() {
        super.viewDidLoad()
        // nothing special here
        tableView.register(EnlargingCell.self, forCellReuseIdentifier: "cell")
        tableView.estimatedRowHeight = 100
        tableView.rowHeight = UITableViewAutomaticDimension
        tableView.allowsSelection = false
        
        // creating some dummy data, 30 items
        for index in 0..<30 {
            modelItems.append("Item \(index)")
        }
        
        let longPressRecognizer = UILongPressGestureRecognizer(target: self, action: #selector(longPress(longPressGestureRecognizer:)))
        longPressRecognizer.minimumPressDuration = 1
        self.view.addGestureRecognizer(longPressRecognizer)
    }
    
    // following three methods should be clear
    override func numberOfSections(in tableView: UITableView) -> Int {
        return 1
    }
    
    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return modelItems.count
    }
    
    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath)
        cell.textLabel?.text = modelItems[indexPath.row]
        return cell
    }
    
    @objc func longPress(longPressGestureRecognizer: UILongPressGestureRecognizer) {
        if longPressGestureRecognizer.state == UIGestureRecognizerState.began {
            let touchPoint = longPressGestureRecognizer.location(in: self.tableView)
            if let indexPath = tableView.indexPathForRow(at: touchPoint),
                let cell = tableView.cellForRow(at: indexPath) as? EnlargingCell {
                //when the press starts on a cell, we will keep the indexPath for the cell
                self.enlargingCell = cell
                // and turn on enlarging
                self.startEnlarging()
            }
        } else if longPressGestureRecognizer.state == .ended {
            // when the press is ended, we can stop enlarging
            stopEnlarging()
        }
    }
    
    func startEnlarging() {
        // interval 0.1 second seems smooth enough (redraw seems to be animated anyway)
        timer = Timer.scheduledTimer(withTimeInterval: 0.1, repeats: true, block: { [weak self] (timer) in
            guard let strongSelf = self, let enlargingCell = self?.enlargingCell else { return }
            
            let oldHeight = enlargingCell.heightConstraint.constant
            // since the timer repeats every 0.1 second, this will enlarge the cell 20 points per second till limit
            // in one cycle I will enlarge the cell by two points
            let newHeight = oldHeight + 2
            if newHeight < strongSelf.limitHeight {
                // if the newHeight did not reach limit,
                // update height and redraw tableView
                enlargingCell.heightConstraint.constant = newHeight
                strongSelf.tableView.beginUpdates()
                strongSelf.tableView.setNeedsLayout()
                strongSelf.tableView.endUpdates()
            } else {
                // reached maximum size, just cancel the timer
                strongSelf.stopEnlarging()
            }
        })
    }
    
    func stopEnlarging() {
        // this just cancels the timer
        timer?.invalidate()
    }
}

class EnlargingCell: UITableViewCell {
    
    var heightConstraint: NSLayoutConstraint!
    
    override init(style: UITableViewCellStyle, reuseIdentifier: String?) {
        super.init(style: .default, reuseIdentifier: reuseIdentifier)
        
        // for the illustration I am using explicit height constraint on contentView, but it could be determined using the content too
        
        heightConstraint = self.contentView.heightAnchor.constraint(equalToConstant: 100)
        // priority set to 999 because of https://stackoverflow.com/questions/44651241/expandable-uitableview-cell-using-autolayout-results-in-uiviewalertforunsatisfia
        heightConstraint.priority = UILayoutPriority(rawValue: 999)
        heightConstraint.isActive = true
    }
    
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}