How one can create a desk view programmatically?
Let’s soar straight into the coding half, however first: begin Xcode, create a brand new iOS single view app venture, enter some identify & particulars for the venture as regular, use Swift and at last open the ViewController.swift file instantly. Now seize your keyboard! ⌨️
Professional tip: use Cmd+Shift+O to rapidly soar between recordsdata
I am not going to make use of interface builder on this tutorial, so how will we create views programmatically? There’s a technique referred to as loadView that is the place you need to add customized views to your view hierarchy. You’ll be able to possibility+click on the tactic identify in Xcode & learn the dialogue about loadView technique, however let me summarize the entire thing.
We’ll use a weak property to carry a reference to our desk view. Subsequent, we override the loadView technique & name tremendous, to be able to load the controller’s self.view property with a view object (from a nib or a storyboard file if there’s one for the controller). After that we assign our model new view to a neighborhood property, flip off system supplied structure stuff, and insert our desk view into our view hierarchy. Lastly we create some actual constraints utilizing anchors & save our pointer to our weak property. Simple! 🤪
class ViewController: UIViewController {
weak var tableView: UITableView!
override func loadView() {
tremendous.loadView()
let tableView = UITableView(body: .zero, model: .plain)
tableView.translatesAutoresizingMaskIntoConstraints = false
self.view.addSubview(tableView)
NSLayoutConstraint.activate([
self.view.safeAreaLayoutGuide.topAnchor.constraint(equalTo: tableView.topAnchor),
self.view.safeAreaLayoutGuide.bottomAnchor.constraint(equalTo: tableView.bottomAnchor),
self.view.leadingAnchor.constraint(equalTo: tableView.leadingAnchor),
self.view.trailingAnchor.constraint(equalTo: tableView.trailingAnchor),
])
self.tableView = tableView
}
}All the time use auto structure anchors to specify view constraints, if you do not know how one can use them, test my structure anchors tutorial, it is takes solely about quarter-hour to study this API, and you will not remorse it. It is an especially useful gizmo for any iOS developer! 😉
You would possibly ask: ought to I exploit weak or robust properties for view references? I would say in many of the instances if you’re not overriding self.view you need to use weak! The view hierarchy will maintain your customized view by means of a robust reference, so there isn’t any want for silly retain cycles & reminiscence leaks. Belief me! 🤥
UITableViewDataSource fundamentals
Okay, we’ve got an empty desk view, let’s show some cells! With the intention to fill our desk view with actual knowledge, we’ve got to evolve to the UITableViewDataSource protocol. By a easy delegate sample, we are able to present varied info for the UITableView class, so it’s going to to know the way a lot sections and rows might be wanted, what sort of cells needs to be displayed for every row, and plenty of extra little particulars.
One other factor is that UITableView is a extremely environment friendly class. It’s going to reuse all of the cells which are at present not displayed on the display screen, so it’s going to eat manner much less reminiscence than a UIScrollView, if it’s a must to take care of tons of or hundreds of things. To help this conduct we’ve got to register our cell class with a reuse identifier, so the underlying system will know what sort of cell is required for a particular place. ⚙️
class ViewController: UIViewController {
var objects: [String] = [
"👽", "🐱", "🐔", "🐶", "🦊", "🐵", "🐼", "🐷", "💩", "🐰",
"🤖", "🦄", "🐻", "🐲", "🦁", "💀", "🐨", "🐯", "👻", "🦖",
]
override func viewDidLoad() {
tremendous.viewDidLoad()
self.tableView.register(UITableViewCell.self, forCellReuseIdentifier: "UITableViewCell")
self.tableView.dataSource = self
}
}
extension ViewController: UITableViewDataSource {
func tableView(_ tableView: UITableView, numberOfRowsInSection part: Int) -> Int {
return self.objects.rely
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "UITableViewCell", for: indexPath)
let merchandise = self.objects[indexPath.item]
cell.textLabel?.textual content = merchandise
return cell
}
}After including a number of strains of code to our view controller file, the desk view is now capable of show a pleasant record of emojis! We’re utilizing the built-in UITableViewCell class from UIKit, which comes actually helpful if you’re good to go together with the “iOS-system-like” cell designs. We additionally conformed to the information supply protocol, by telling what number of objects are in our part (at present there is just one part), and we configured our cell contained in the well-known cell for row at indexPath delegate technique. 😎
Customizing desk view cells
UITableViewCell can present some primary components to show knowledge (title, element, picture in several kinds), however normally you may want customized cells. Here’s a primary template of a customized cell subclass, I am going to clarify all of the strategies after the code.
class MyCell: UITableViewCell {
override init(model: UITableViewCell.CellStyle, reuseIdentifier: String?) {
tremendous.init(model: model, reuseIdentifier: reuseIdentifier)
self.initialize()
}
required init?(coder aDecoder: NSCoder) {
tremendous.init(coder: aDecoder)
self.initialize()
}
func initialize() {
}
override func prepareForReuse() {
tremendous.prepareForReuse()
}
}The init(model:reuseIdentifier) technique is a superb place to override the cell model property if you will use the default UITableViewCell programmatically, however with totally different kinds (there isn’t any choice to set cellStyle after the cell was initialized). For instance for those who want a .value1 styled cell, simply cross the argument on to the tremendous name. This manner you possibly can profit from the 4 predefined cell kinds.
You will additionally must implement
init(coder:), so you need to create a standard initialize() operate the place you can add your customized views to the view hierarchy, like we did within the loadView technique above. In case you are utilizing xib recordsdata & IB, you should use the awakeFromNib technique so as to add further model to your views by means of the usual@IBOutletproperties (or add further views to the hierarchy as properly). 👍
The final technique that we’ve got to speak about is prepareForReuse. As I discussed earlier than cells are being reused so if you wish to reset some properties, just like the background of a cell, you are able to do it right here. This technique might be referred to as earlier than the cell goes to be reused.
Let’s make two new cell subclasses to mess around with.
class DetailCell: UITableViewCell {
override init(model: UITableViewCell.CellStyle, reuseIdentifier: String?) {
tremendous.init(model: .subtitle, reuseIdentifier: reuseIdentifier)
self.initialize()
}
required init?(coder aDecoder: NSCoder) {
tremendous.init(coder: aDecoder)
self.initialize()
}
func initialize() {
}
override func prepareForReuse() {
tremendous.prepareForReuse()
self.textLabel?.textual content = nil
self.detailTextLabel?.textual content = nil
self.imageView?.picture = nil
}
}Our customized cell could have a giant picture background plus a title label within the heart of the view with a customized sized system font. Additionally I’ve added the Swift emblem as an asset to the venture, so we are able to have a pleasant demo picture. 🖼
class CustomCell: UITableViewCell {
weak var coverView: UIImageView!
weak var titleLabel: UILabel!
override init(model: UITableViewCell.CellStyle, reuseIdentifier: String?) {
tremendous.init(model: model, reuseIdentifier: reuseIdentifier)
self.initialize()
}
required init?(coder aDecoder: NSCoder) {
tremendous.init(coder: aDecoder)
self.initialize()
}
func initialize() {
let coverView = UIImageView(body: .zero)
coverView.translatesAutoresizingMaskIntoConstraints = false
self.contentView.addSubview(coverView)
self.coverView = coverView
let titleLabel = UILabel(body: .zero)
titleLabel.translatesAutoresizingMaskIntoConstraints = false
self.contentView.addSubview(titleLabel)
self.titleLabel = titleLabel
NSLayoutConstraint.activate([
self.contentView.topAnchor.constraint(equalTo: self.coverView.topAnchor),
self.contentView.bottomAnchor.constraint(equalTo: self.coverView.bottomAnchor),
self.contentView.leadingAnchor.constraint(equalTo: self.coverView.leadingAnchor),
self.contentView.trailingAnchor.constraint(equalTo: self.coverView.trailingAnchor),
self.contentView.centerXAnchor.constraint(equalTo: self.titleLabel.centerXAnchor),
self.contentView.centerYAnchor.constraint(equalTo: self.titleLabel.centerYAnchor),
])
self.titleLabel.font = UIFont.systemFont(ofSize: 64)
}
override func prepareForReuse() {
tremendous.prepareForReuse()
self.coverView.picture = nil
}
}That is it, let’s begin utilizing these new cells. I am going to even inform you how one can set customized peak for a given cell, and how one can deal with cell choice correctly, however first we have to get to know with one other delegate protocol. 🤝
Primary UITableViewDelegate tutorial
This delegate is accountable for plenty of issues, however for now we’ll cowl just some attention-grabbing elements, like how one can deal with cell choice & present a customized cell peak for every objects contained in the desk. Here’s a fast pattern code.
class ViewController: UIViewController {
override func viewDidLoad() {
tremendous.viewDidLoad()
self.tableView.register(UITableViewCell.self, forCellReuseIdentifier: "UITableViewCell")
self.tableView.register(DetailCell.self, forCellReuseIdentifier: "DetailCell")
self.tableView.register(CustomCell.self, forCellReuseIdentifier: "CustomCell")
self.tableView.dataSource = self
self.tableView.delegate = self
}
}
extension ViewController: UITableViewDataSource {
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "CustomCell", for: indexPath) as! CustomCell
let merchandise = self.objects[indexPath.item]
cell.titleLabel.textual content = merchandise
cell.coverView.picture = UIImage(named: "Swift")
return cell
}
}
extension ViewController: UITableViewDelegate {
func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
return 128
}
func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
tableView.deselectRow(at: indexPath, animated: true)
let merchandise = self.objects[indexPath.item]
let alertController = UIAlertController(title: merchandise, message: "is in da home!", preferredStyle: .alert)
let motion = UIAlertAction(title: "Okay", model: .default) { _ in }
alertController.addAction(motion)
self.current(alertController, animated: true, completion: nil)
}
}As you possibly can see I am registering my model new customized cell courses within the viewDidLoad technique. I additionally modified the code contained in the cellForRowAt indexPath technique, so we are able to use the CustomCell class as a substitute of UITableViewCells. Do not be afraid of pressure casting right here, if one thing goes flawed at this level, your app ought to crash. 🙃
There are two delegate strategies that we’re utilizing right here. Within the first one, we’ve got to return a quantity and the system will use that peak for the cells. If you wish to use totally different cell peak per row, you possibly can obtain that too by checking indexPath property or something like that. The second is the handler for the choice. If somebody faucets on a cell, this technique might be referred to as & you possibly can carry out some motion.
An indexPath has two attention-grabbing properties: part & merchandise (=row)
A number of sections with headers and footers
It is attainable to have a number of sections contained in the desk view, I will not go an excessive amount of into the main points, as a result of it is fairly simple. You simply have to make use of indexPaths to be able to get / set / return the correct knowledge for every part & cell.
import UIKit
class ViewController: UIViewController {
weak var tableView: UITableView!
var placeholderView = UIView(body: .zero)
var isPullingDown = false
enum Model {
case `default`
case subtitle
case customized
}
var model = Model.default
var objects: [String: [String]] = [
"Originals": ["👽", "🐱", "🐔", "🐶", "🦊", "🐵", "🐼", "🐷", "💩", "🐰","🤖", "🦄"],
"iOS 11.3": ["🐻", "🐲", "🦁", "💀"],
"iOS 12": ["🐨", "🐯", "👻", "🦖"],
]
override func loadView() {
tremendous.loadView()
let tableView = UITableView(body: .zero, model: .plain)
tableView.translatesAutoresizingMaskIntoConstraints = false
self.view.addSubview(tableView)
NSLayoutConstraint.activate([
self.view.safeAreaLayoutGuide.topAnchor.constraint(equalTo: tableView.topAnchor),
self.view.safeAreaLayoutGuide.bottomAnchor.constraint(equalTo: tableView.bottomAnchor),
self.view.leadingAnchor.constraint(equalTo: tableView.leadingAnchor),
self.view.trailingAnchor.constraint(equalTo: tableView.trailingAnchor),
])
self.tableView = tableView
}
override func viewDidLoad() {
tremendous.viewDidLoad()
self.tableView.register(UITableViewCell.self, forCellReuseIdentifier: "UITableViewCell")
self.tableView.register(DetailCell.self, forCellReuseIdentifier: "DetailCell")
self.tableView.register(CustomCell.self, forCellReuseIdentifier: "CustomCell")
self.tableView.dataSource = self
self.tableView.delegate = self
self.tableView.separatorStyle = .singleLine
self.tableView.separatorColor = .lightGray
self.tableView.separatorInset = .zero
self.navigationItem.rightBarButtonItem = .init(barButtonSystemItem: .refresh, goal: self, motion: #selector(self.toggleCells))
}
@objc func toggleCells() {
swap self.model {
case .default:
self.model = .subtitle
case .subtitle:
self.model = .customized
case .customized:
self.model = .default
}
DispatchQueue.foremost.async {
self.tableView.reloadData()
}
}
func key(for part: Int) -> String {
let keys = Array(self.objects.keys).sorted { first, final -> Bool in
if first == "Originals" {
return true
}
return first < final
}
let key = keys[section]
return key
}
func objects(in part: Int) -> [String] {
let key = self.key(for: part)
return self.objects[key]!
}
func merchandise(at indexPath: IndexPath) -> String {
let objects = self.objects(in: indexPath.part)
return objects[indexPath.item]
}
}
extension ViewController: UITableViewDataSource {
func numberOfSections(in tableView: UITableView) -> Int {
return self.objects.keys.rely
}
func tableView(_ tableView: UITableView, numberOfRowsInSection part: Int) -> Int {
return self.objects(in: part).rely
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let merchandise = self.merchandise(at: indexPath)
let cell = tableView.dequeueReusableCell(withIdentifier: "CustomCell", for: indexPath) as! CustomCell
cell.titleLabel.textual content = merchandise
cell.coverView.picture = UIImage(named: "Swift")
return cell
}
func tableView(_ tableView: UITableView, titleForHeaderInSection part: Int) -> String? {
return self.key(for: part)
}
}
extension ViewController: UITableViewDelegate {
func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
return 128
}
func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
tableView.deselectRow(at: indexPath, animated: true)
let merchandise = self.merchandise(at: indexPath)
let alertController = UIAlertController(title: merchandise, message: "is in da home!", preferredStyle: .alert)
let motion = UIAlertAction(title: "Okay", model: .default) { _ in }
alertController.addAction(motion)
self.current(alertController, animated: true, completion: nil)
}
}Though there’s one attention-grabbing addition within the code snippet above. You’ll be able to have a customized title for each part, you simply have so as to add the titleForHeaderInSection knowledge supply technique. Yep, it appears to be like like shit, however this one isn’t about good UIs. 😂
Nonetheless if you’re not glad with the structure of the part titles, you possibly can create a customized class & use that as a substitute of the built-in ones. Right here is how one can do a customized part header view. Right here is the implementation of the reusable view:
class HeaderView: UITableViewHeaderFooterView {
weak var titleLabel: UILabel!
override init(reuseIdentifier: String?) {
tremendous.init(reuseIdentifier: reuseIdentifier)
self.initialize()
}
required init?(coder aDecoder: NSCoder) {
tremendous.init(coder: aDecoder)
self.initialize()
}
func initialize() {
let titleLabel = UILabel(body: .zero)
titleLabel.translatesAutoresizingMaskIntoConstraints = false
self.contentView.addSubview(titleLabel)
self.titleLabel = titleLabel
NSLayoutConstraint.activate([
self.contentView.centerXAnchor.constraint(equalTo: self.titleLabel.centerXAnchor),
self.contentView.centerYAnchor.constraint(equalTo: self.titleLabel.centerYAnchor),
])
self.contentView.backgroundColor = .black
self.titleLabel.font = UIFont.boldSystemFont(ofSize: 16)
self.titleLabel.textAlignment = .heart
self.titleLabel.textColor = .white
}
}There’s only some issues left to do, it’s a must to register your header view, similar to you probably did it for the cells. It is precisely the identical manner, besides that there’s a separate registration “pool” for the header & footer views. Lastly it’s a must to implement two extra, however comparatively easy (and acquainted) delegate strategies.
extension ViewController: UITableViewDelegate {
func tableView(_ tableView: UITableView, heightForHeaderInSection part: Int) -> CGFloat {
return 32
}
func tableView(_ tableView: UITableView, viewForHeaderInSection part: Int) -> UIView? {
let view = tableView.dequeueReusableHeaderFooterView(withIdentifier: "HeaderView") as! HeaderView
view.titleLabel.textual content = self.key(for: part)
return view
}
}Footers works precisely the identical as headers, you simply must implement the corresponding knowledge supply & delegate strategies to be able to help them.
You’ll be able to even have a number of cells in the identical desk view based mostly on the row or part index or any particular enterprise requirement. I am not going to demo this right here, as a result of I’ve a manner higher answer for mixing and reusing cells contained in the CoreKit framework. It is already there for desk views as properly, plus I already coated this concept in my final assortment view tutorial put up. You need to test that too. 🤓
Part titles & indexes
Okay, in case your mind isn’t melted but, I am going to present you two extra little issues that may be attention-grabbing for newcomers. The primary one is predicated on two extra knowledge supply strategies and it is a very nice addition for lengthy lists. (I favor search bars!) 🤯
extension ViewController: UITableViewDataSource {
func sectionIndexTitles(for tableView: UITableView) -> [String]? {
return ["1", "2", "3"]
}
func tableView(_ tableView: UITableView, sectionForSectionIndexTitle title: String, at index: Int) -> Int {
return index
}
}If you will implement these strategies above you possibly can have a bit index view in your sections in the suitable aspect of the desk view, so the end-user will have the ability to rapidly soar between sections. Similar to within the official contacts app. 📕
Choice vs spotlight
Cells are highlighted when you’re holding them down together with your finger. Cell goes to be chosen for those who launch your finger from the cell.
Do not over-complicate this. You simply must implement two strategies in you customized cell class to make the whole lot work. I favor to deselect my cells instantly, if they are not for instance utilized by some type of knowledge picker structure. Right here is the code:
class CustomCell: UITableViewCell {
override func setSelected(_ chosen: Bool, animated: Bool) {
self.coverView.backgroundColor = chosen ? .purple : .clear
}
override func setHighlighted(_ highlighted: Bool, animated: Bool) {
self.coverView.backgroundColor = highlighted ? .blue : .clear
}
}As you possibly can see, it is ridiculously straightforward, however many of the newcomers do not know the way to do that. Additionally they normally neglect to reset cells earlier than the reusing logic occurs, so the record retains messing up cell states. Don’t be concerned an excessive amount of about these issues, they’re going to go away as you are going to be extra skilled with the UITableView APIs.
