create a desk view programmatically?
Let’s bounce straight into the coding half, however first: begin Xcode, create a brand new iOS single view app undertaking, enter some identify & particulars for the undertaking as common, use Swift and eventually open the ViewController.swift file instantly. Now seize your keyboard! ⌨️
Professional tip: use Cmd+Shift+O to rapidly bounce between recordsdata
I am not going to make use of interface builder on this tutorial, so how can we create views programmatically? There’s a methodology known as loadView that is the place it’s best to add customized views to your view hierarchy. You possibly can choice+click on the tactic identify in Xcode & learn the dialogue about loadView methodology, 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 methodology & name tremendous, so as 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 offered 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 the right way to use them, examine 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 may ask: ought to I take advantage of weak or sturdy properties for view references? I might say in a lot of the instances if you’re not overriding self.view it’s best to use weak! The view hierarchy will maintain your customized view by a robust reference, so there isn’t any want for silly retain cycles & reminiscence leaks. Belief me! 🤥
UITableViewDataSource fundamentals
Okay, now we have an empty desk view, let’s show some cells! With a view to fill our desk view with actual knowledge, now we have to evolve to the UITableViewDataSource protocol. By means of a easy delegate sample, we will present numerous info for the UITableView class, so it’s going to to understand how a lot sections and rows shall 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 very environment friendly class. It will reuse all of the cells which are at present not displayed on the display, so it’s going to devour method much less reminiscence than a UIScrollView, if it’s important to take care of tons of or 1000’s of things. To help this conduct now we have 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 gadgets: [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.gadgets.depend
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "UITableViewCell", for: indexPath)
let merchandise = self.gadgets[indexPath.item]
cell.textLabel?.textual content = merchandise
return cell
}
}After including a couple of traces of code to our view controller file, the desk view is now capable of show a pleasant checklist of emojis! We’re utilizing the built-in UITableViewCell class from UIKit, which comes actually useful 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 gadgets 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 methodology. 😎
Customizing desk view cells
UITableViewCell can present some fundamental components to show knowledge (title, element, picture in several kinds), however normally you may want customized cells. Here’s a fundamental 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) methodology is a good 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 move the argument on to the tremendous name. This fashion you possibly can profit from the 4 predefined cell kinds.
You may additionally should implement
init(coder:), so it’s best to create a standard initialize() perform the place you can add your customized views to the view hierarchy, like we did within the loadView methodology above. In case you are utilizing xib recordsdata & IB, you should utilize the awakeFromNib methodology so as to add further model to your views by the usual@IBOutletproperties (or add further views to the hierarchy as nicely). 👍
The final methodology that now we have 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 methodology shall be known 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 brand as an asset to the undertaking, so we will 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 the right way to set customized top for a given cell, and the right way to 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 many issues, however for now we’ll cowl just some attention-grabbing features, like the right way to deal with cell choice & present a customized cell top for every gadgets 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.gadgets[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.gadgets[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 lessons within the viewDidLoad methodology. I additionally modified the code contained in the cellForRowAt indexPath methodology, so we will use the CustomCell class as an alternative of UITableViewCells. Do not be afraid of drive casting right here, if one thing goes unsuitable at this level, your app ought to crash. 🙃
There are two delegate strategies that we’re utilizing right here. Within the first one, now we have to return a quantity and the system will use that top for the cells. If you wish to use totally different cell top 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 methodology shall be known 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 small print, as a result of it is fairly simple. You simply have to make use of indexPaths so as to get / set / return the right knowledge for every part & cell.
import UIKit
class ViewController: UIViewController {
weak var tableView: UITableView!
var placeholderView = UIView(body: .zero)
var isPullingDown = false
enum Fashion {
case `default`
case subtitle
case customized
}
var model = Fashion.default
var gadgets: [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.predominant.async {
self.tableView.reloadData()
}
}
func key(for part: Int) -> String {
let keys = Array(self.gadgets.keys).sorted { first, final -> Bool in
if first == "Originals" {
return true
}
return first < final
}
let key = keys[section]
return key
}
func gadgets(in part: Int) -> [String] {
let key = self.key(for: part)
return self.gadgets[key]!
}
func merchandise(at indexPath: IndexPath) -> String {
let gadgets = self.gadgets(in: indexPath.part)
return gadgets[indexPath.item]
}
}
extension ViewController: UITableViewDataSource {
func numberOfSections(in tableView: UITableView) -> Int {
return self.gadgets.keys.depend
}
func tableView(_ tableView: UITableView, numberOfRowsInSection part: Int) -> Int {
return self.gadgets(in: part).depend
}
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 possibly can have a customized title for each part, you simply have so as to add the titleForHeaderInSection knowledge supply methodology. Yep, it seems like shit, however this one shouldn’t be 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 an alternative of the built-in ones. Right here is the right way to 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 may be only some issues left to do, it’s important to register your header view, identical to you probably did it for the cells. It is precisely the identical method, besides that there’s a separate registration “pool” for the header & footer views. Lastly it’s important to implement two further, 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 should implement the corresponding knowledge supply & delegate strategies so as to help them.
You possibly can even have a number of cells in the identical desk view primarily based 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 method higher answer for mixing and reusing cells contained in the CoreKit framework. It is already there for desk views as nicely, plus I already coated this concept in my final assortment view tutorial submit. It’s best to examine that too. 🤓
Part titles & indexes
Okay, in case your mind shouldn’t be melted but, I am going to present you two extra little issues that may be attention-grabbing for freshmen. The primary one is predicated on two further 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 to your sections in the precise aspect of the desk view, so the end-user will have the ability to rapidly bounce between sections. Identical to within the official contacts app. 📕
Choice vs spotlight
Cells are highlighted if you find yourself 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 should implement two strategies in you customized cell class to make every little thing work. I favor to deselect my cells instantly, if they don’t seem to be for instance utilized by some kind of knowledge picker structure. Right here is the code:
class CustomCell: UITableViewCell {
override func setSelected(_ chosen: Bool, animated: Bool) {
self.coverView.backgroundColor = chosen ? .pink : .clear
}
override func setHighlighted(_ highlighted: Bool, animated: Bool) {
self.coverView.backgroundColor = highlighted ? .blue : .clear
}
}As you possibly can see, it is ridiculously simple, however a lot of the freshmen do not understand how to do that. Additionally they normally overlook to reset cells earlier than the reusing logic occurs, so the checklist retains messing up cell states. Don’t be concerned an excessive amount of about these issues, they will go away as you are going to be extra skilled with the UITableView APIs.