Table View Section Index List

playground.swift

//: Playground - noun: a place where people can play

import UIKit
import Foundation
import PlaygroundSupport

let allStates = ["Alaska",
              "Alabama",
              "Arkansas",
              "American Samoa",
              "Arizona",
              "California",
              "Colorado",
              "Connecticut",
              "District of Columbia",
              "Delaware",
              "Florida",
              "Georgia",
              "Guam",
              "Hawaii",
              "Iowa",
              "Idaho",
              "Illinois",
              "Indiana",
              "Kansas",
              "Kentucky",
              "Louisiana",
              "Massachusetts",
              "Maryland",
              "Maine",
              "Michigan",
              "Minnesota",
              "Missouri",
              "Mississippi",
              "Montana",
              "North Carolina",
              "North Dakota",
              "Nebraska",
              "New Hampshire",
              "New Jersey",
              "New Mexico",
              "Nevada",
              "New York",
              "Ohio",
              "Oklahoma",
              "Oregon",
              "Pennsylvania",
              "Puerto Rico",
              "Rhode Island",
              "South Carolina",
              "South Dakota",
              "Tennessee",
              "Texas",
              "Utah",
              "Virginia",
              "Virgin Islands",
              "Vermont",
              "Washington",
              "Wisconsin",
              "West Virginia",
              "Wyoming"]

struct State {
	let name: String
}

class MyViewController: UIViewController {

	let collation = UILocalizedIndexedCollation.current()
	var sectionTitles: [String] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ".characters.map { String($0) }
	var sections: [[State]] = []
	var states: [State] = [] {
		didSet {
			sections = Array(repeating: [], count: sectionTitles.count)

			let sortedStates = states.sorted { (lhs, rhs) -> Bool in
				lhs.name < rhs.name
			}

			for state in sortedStates {
				guard
					let first = state.name.characters.first,
					let sectionIndex = sectionTitles.index(of: String(first)) else { return }
				sections[sectionIndex].append(state)

			}

			self.tableView.reloadData()

		}
	}

	lazy var tableView: UITableView = {
		let tableView = UITableView(frame: .zero)
		tableView.delegate = self
		tableView.dataSource = self
		tableView.backgroundColor = .white
		self.view.addSubview(tableView)
		return tableView
	}()

	override func viewDidLoad() {
		super.viewDidLoad()
		self.view.backgroundColor = .white
		tableView.topAnchor.constraint(equalTo: self.view.topAnchor).isActive = true
		tableView.leftAnchor.constraint(equalTo: self.view.leftAnchor).isActive = true
		tableView.rightAnchor.constraint(equalTo: self.view.rightAnchor).isActive = true
		tableView.bottomAnchor.constraint(equalTo: self.view.bottomAnchor).isActive = true
		tableView.translatesAutoresizingMaskIntoConstraints = false
		states
		loadStates()
	}

	func loadStates() {
		states = allStates.map { .init(name: $0) }
	}

}

extension MyViewController: UITableViewDelegate {}

extension MyViewController: UITableViewDataSource {
	func numberOfSections(in tableView: UITableView) -> Int {
		print(sections.count)
		return sections.count
	}

	func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
		print(sections[section].count)
		return sections[section].count
	}

	func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
		let cell = UITableViewCell()
		cell.textLabel?.text = sections[indexPath.section][indexPath.row].name
		return cell
	}

	func sectionIndexTitles(for tableView: UITableView) -> [String]? {
		return sectionTitles
	}

	func tableView(_ tableView: UITableView, sectionForSectionIndexTitle title: String, at index: Int) -> Int {
		return index
	}
}

PlaygroundPage.current.liveView = MyViewController()