The right way to 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 challenge, enter some identify & particulars for the challenge as typical, use Swift and at last open the ViewController.swift file straight away. Now seize your keyboard! ⌨️
Professional tip: use Cmd+Shift+O to rapidly soar between information
I am not going to make use of interface builder on this tutorial, so how will we create views programmatically? There’s a methodology referred to as loadView that is the place it’s best to add customized views to your view hierarchy. You possibly can choice+click on the strategy 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, in an effort to load the controller’s self.view property with a view object (from a nib or a storyboard file if there may be one for the controller). After that we assign our model new view to a neighborhood property, flip off system offered format 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. Straightforward! 🤪
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 format anchors to specify view constraints, if you do not know the best way to use them, examine my format anchors tutorial, it is takes solely about quarter-hour to study this API, and you will not remorse it. It is an especially great tool for any iOS developer! 😉
You may ask: ought to I exploit weak or robust properties for view references? I might say in many of the circumstances in case you are not overriding self.view it’s best to use weak! The view hierarchy will maintain your customized view by a powerful reference, so there isn’t a 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 a purpose to fill our desk view with actual information, we’ve got to evolve to the UITableViewDataSource protocol. Via a easy delegate sample, we will present numerous info for the UITableView class, so it’s going to to know the way a lot sections and rows will likely be wanted, what sort of cells must be displayed for every row, and lots 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 the moment not displayed on the display, so it’s going to devour method much less reminiscence than a UIScrollView, if you need to cope with a whole bunch or 1000’s of things. To assist 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 selected 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.rely
}
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 just a few traces of code to our view controller file, the desk view is now in a position to show a pleasant listing of emojis! We’re utilizing the built-in UITableViewCell class from UIKit, which comes actually helpful in case you are good to go together with the “iOS-system-like” cell designs. We additionally conformed to the info supply protocol, by telling what number of gadgets are in our part (at the moment 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 primary parts to show information (title, element, picture in several types), however often 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) methodology is a good place to override the cell model property if you’ll use the default UITableViewCell programmatically, however with totally different types (there isn’t a choice to set cellStyle after the cell was initialized). For instance in case you 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 types.
You will additionally must implement
init(coder:), so it’s best to create a typical initialize() operate the place you’ll add your customized views to the view hierarchy, like we did within the loadView methodology above. If you’re utilizing xib information & 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 effectively). 👍
The final methodology 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 methodology will likely 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 middle of the view with a customized sized system font. Additionally I’ve added the Swift brand as an asset to the challenge, 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 let you know the best way to set customized top for a given cell, and the best 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 plenty of issues, however for now we will cowl just some fascinating facets, like the best 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 courses 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 improper 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 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 will likely be referred to as & you possibly can carry out some motion.
An indexPath has two fascinating 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 in an effort to get / set / return the right information 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.fundamental.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.rely
}
func tableView(_ tableView: UITableView, numberOfRowsInSection part: Int) -> Int {
return self.gadgets(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 may be one fascinating 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 information supply methodology. Yep, it seems to be like shit, however this one shouldn’t be about excellent UIs. 😂
Nevertheless in case you are not glad with the format 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 best 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 = .middle
self.titleLabel.textColor = .white
}
}There may be just a few issues left to do, you need 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 you need 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 must implement the corresponding information supply & delegate strategies in an effort to assist them.
You possibly can 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 method higher answer for mixing and reusing cells contained in the CoreKit framework. It is already there for desk views as effectively, plus I already coated this concept in my final assortment view tutorial submit. You must 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 fascinating for freshmen. The primary one is predicated on two further information 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’ll implement these strategies above you possibly can have a little bit index view in your sections in the fitting aspect of the desk view, so the end-user will be capable of rapidly soar 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 in case you launch your finger from the cell.
Do not over-complicate this. You simply must implement two strategies in you customized cell class to make every little thing work. I favor to deselect my cells straight away, if they are not for instance utilized by some type of information picker format. Right here is the code:
class CustomCell: UITableViewCell {
override func setSelected(_ chosen: Bool, animated: Bool) {
self.coverView.backgroundColor = chosen ? .crimson : .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 freshmen do not know the way to do that. Additionally they often neglect to reset cells earlier than the reusing logic occurs, so the listing retains messing up cell states. Don’t fret 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.
