Set placeholder text to TextView in iOS Swift 4

DemoViewController.swift

//
//  DemoViewController.swift
//  Samples
//
//  Created by VikasK on 27/02/19.
//  Copyright © 2019 Vikaskore Software. All rights reserved.

import UIKit

class DemoViewController: UIViewController, UITableViewDelegate, UITableViewDataSource, UITextFieldDelegate, UITextViewDelegate {
    
    @IBOutlet var contactTableView: UITableView!
    var placeholder = "Please comment here..."
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        //.lightGray : placeholder text color
        //.black : text color
    }
    
    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "TxtViewTableViewCell") as! TxtViewTableViewCell
        cell.txtView.text = placeholder
        if placeholder == "Please comment here..." {
            cell.txtView.textColor = .lightGray
        } else {
            cell.txtView.textColor = .black
        }
        return cell
    }
    
    //MARK:- TextView Delegates
    
    func textViewDidBeginEditing(_ textView: UITextView) {
        if textView.textColor == .lightGray {
            textView.text = nil
            textView.textColor = .black
        }
    }
    
    func textViewDidEndEditing(_ textView: UITextView) {
        if textView.text.isEmpty {
            textView.text = "Please comment here..."
            textView.textColor = UIColor.lightGray
            placeholder = ""
        } else {
            placeholder = textView.text
        }
    }
    
    func textViewDidChange(_ textView: UITextView) {
        placeholder = textView.text
    }
    
    /*
     To print remaining allowed characters(Suppose you have 20 character limit)
     countingLabel is to display number of remaining character user can enter in textView, like: 10/20, 9/20
     */
     @IBOutlet var countingLabel: UILabel!
    
    func textViewDidChange(_ textView: UITextView) {
        countingLabel.text = "\(20 - textView.text.count)/20"
    }
    
    func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {
        return textView.text.count + (text.count - range.length) <= 20
    }
    
    
    //MARK:- Button Action
    
    func sendButtonTapped() {
        self.view.endEditing(true)
        //send logic goes here
    }
}