UITableView+EmptyView.swift

//
//  UITableView+EmptyView.swift
//  StickerTweet
//
//  Created by Swapnanil Dhol on 7/6/20.
//  Copyright © 2020 Swapnanil Dhol. All rights reserved.
//

import UIKit

extension UITableView {
    func setEmptyView(title: String, message: String) {
        let emptyView = UIView(frame: CGRect(x: self.center.x,
                                             y: self.center.y,
                                             width: self.bounds.size.width,
                                             height: self.bounds.size.height))
        let titleLabel = UILabel()
        titleLabel.translatesAutoresizingMaskIntoConstraints = false
        titleLabel.textColor = .label
        titleLabel.font = .systemFont(ofSize: 18, weight: .bold)
        titleLabel.text = title
        titleLabel.numberOfLines = 0
        titleLabel.textAlignment = .center

        let messageLabel = UILabel()
        messageLabel.translatesAutoresizingMaskIntoConstraints = false
        messageLabel.textColor = .secondaryLabel
        messageLabel.font = .systemFont(ofSize: 17, weight: .medium)
        messageLabel.text = message
        messageLabel.numberOfLines = 0
        messageLabel.textAlignment = .center

        emptyView.addSubview(titleLabel)
        emptyView.addSubview(messageLabel)
        NSLayoutConstraint.activate([
            titleLabel.centerYAnchor.constraint(equalTo: emptyView.centerYAnchor),
            titleLabel.centerXAnchor.constraint(equalTo: emptyView.centerXAnchor),
            titleLabel.leadingAnchor.constraint(equalTo: emptyView.leadingAnchor, constant: 20),
            titleLabel.trailingAnchor.constraint(equalTo: emptyView.trailingAnchor, constant: -20),
            messageLabel.topAnchor.constraint(equalTo: titleLabel.bottomAnchor, constant: 10),
            messageLabel.leadingAnchor.constraint(equalTo: emptyView.leadingAnchor, constant: 20),
            messageLabel.trailingAnchor.constraint(equalTo: emptyView.trailingAnchor, constant: -20)
        ])
        self.backgroundView = emptyView
        self.separatorStyle = .none
    }
    func restore() {
        self.backgroundView = nil
        self.separatorStyle = .singleLine
    }
}

//MARK: - Usage 

    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
      //This code uses the NSFRC from CoreData's stack introduced in iOS 13. The basic idea is to show the empty view
      //when the array containing the elements is empty.
      //Return the setEmptyView function right before returning 0
        guard let sections = fetchedResultsController.sections else {
            tableView.setEmptyView(title: "Saved Tweets and Notes will show up here.",
                                   message: "Tap the + button to get started.")
            return 0
        }
        let sectionInfo = sections[section]
        if sectionInfo.numberOfObjects == 0 {
            tableView.setEmptyView(title: "Saved Tweets and Notes will show up here.",
                                   message: "Tap the + button to get started.")
        } else {
            tableView.restore()
        }
        return sectionInfo.numberOfObjects
    }