ScrollToBottomTest

ScrollToBottomTest.swift

import UIKit

extension UITableView {
    
    func scrollToBottom(){
        DispatchQueue.main.async {
            let indexPath = IndexPath(
                row: self.numberOfRows(inSection:  self.numberOfSections-1) - 1,
                section: self.numberOfSections - 1)
            if self.hasRowAtIndexPath(indexPath: indexPath) {
                self.scrollToRow(at: indexPath, at: .bottom, animated: false)
            }
        }
    }
    
    func hasRowAtIndexPath(indexPath: IndexPath) -> Bool {
        return indexPath.section < self.numberOfSections && indexPath.row < self.numberOfRows(inSection: indexPath.section)
    }
    
}

class ViewController: UITableViewController {
    
    private var data: [String] = .init()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        tableView.separatorStyle = .none
        tableView.backgroundColor = .systemGroupedBackground
        tableView.contentInset = UIEdgeInsets(top: 6, left: 0, bottom: 6, right: 0)
        
        tableView.register(TableViewCell.self, forCellReuseIdentifier: "cell")
        
        // Do any additional setup after loading the view.
    }
    
    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        
        DispatchQueue.main.asyncAfter(deadline: .now()+1) {
            let message = "This is an another test message. "
            for i in 1...7 {
                self.data.append(String(repeating: message, count: i))
            }
            self.tableView.reloadData()
            self.tableView.scrollToBottom()
        }
        
    }
    
    override func numberOfSections(in tableView: UITableView) -> Int {
        return data.count
    }
    
    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return 1
    }
    
    override func tableView(_ tableView: UITableView, estimatedHeightForRowAt indexPath: IndexPath) -> CGFloat {
        return 1000
    }
    
    override func tableView(_ tableView: UITableView, titleForHeaderInSection section: Int) -> String? {
        return "\(section)"
    }
    
    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath) as! TableViewCell
        cell.label.text = data[indexPath.section]
        return cell
    }
    
    override func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
        UITableView.automaticDimension
    }

}


class TableViewCell: UITableViewCell {
    
    lazy var label: UILabel = {
        let label = UILabel()
        label.translatesAutoresizingMaskIntoConstraints = false
        label.numberOfLines = 0
        label.lineBreakMode = .byWordWrapping
        return label
    }()
    
    lazy var stackView : UIStackView = {
        let view = UIStackView()
        view.translatesAutoresizingMaskIntoConstraints = false
        view.axis = .vertical
        return view
    }()
    
    lazy var bubbleView: UIView = {
        let view = UIView()
        view.translatesAutoresizingMaskIntoConstraints = false
        view.layer.cornerRadius = 4
        view.layer.masksToBounds = true
        view.backgroundColor = .systemGreen
        return view
    }()
    
    override init(style: UITableViewCell.CellStyle, reuseIdentifier: String?) {
        super.init(style: style, reuseIdentifier: reuseIdentifier)
        
        selectionStyle = .none
        backgroundColor = .clear
        
        contentView.addSubview(stackView)
        
        stackView.topAnchor.constraint(equalTo: contentView.topAnchor, constant: 6).isActive = true
        stackView.leadingAnchor.constraint(equalTo: contentView.leadingAnchor, constant: 12).isActive = true
        stackView.trailingAnchor.constraint(equalTo: contentView.trailingAnchor, constant: -12).isActive = true
        stackView.bottomAnchor.constraint(equalTo: contentView.bottomAnchor, constant: -6).isActive = true
        
        bubbleView.addSubview(label)
        
        label.topAnchor.constraint(equalTo: bubbleView.topAnchor, constant: 12).isActive = true
        label.leadingAnchor.constraint(equalTo: bubbleView.leadingAnchor, constant: 12).isActive = true
        label.trailingAnchor.constraint(equalTo: bubbleView.trailingAnchor, constant: -12).isActive = true
        label.bottomAnchor.constraint(equalTo: bubbleView.bottomAnchor, constant: -12).isActive = true
        
        stackView.addArrangedSubview(bubbleView)
        
    }
    
    required init?(coder: NSCoder) {
        fatalError()
    }
}