Discover ways to use UICollectionView, with extremely reusable UIKit parts and a few MVVM sample with out the going nuts with index path calculations.
Anatomy of the UICollectionView class
In case you’re not acquainted with UICollectionView, I’d counsel to get acquainted with this class instantly. They’re the essential constructing blocks for a lot of apps offered by Apple and different third social gathering builders. It’s like UITableView on steroids. Here’s a fast intro about methods to work with them by IB and Swift code. 💻
You may need seen that I’ve a love for steel music. On this tutorial we’re going to construct an Apple Music catalog like look from floor zero utilizing solely the mighty UICollectionView class. Headers, horizontal and vertical scrolling, round photos, so principally virtually all the pieces that you just’ll ever have to construct nice consumer interfaces. 🤘🏻
The way to make a UICollectionView utilizing Interface Builder (IB) in Xcode?
The quick & sincere reply: you shouldn’t use IB!
In case you nonetheless wish to use IB, here’s a actual fast tutorial for completely inexperienced persons:
The primary steps of making your first UICollectionView primarily based display screen are these:
- Drag a UICollectionView object to your view controller
- Set correct constraints on the gathering view
- Set dataSource & delegate of the gathering view
- Prototype your cell structure contained in the controller
- Add constraints to your views contained in the cell
- Set prototype cell class & reuse identifier
- Do some coding:
import UIKit
class MyCell: UICollectionViewCell {
@IBOutlet weak var textLabel: UILabel!
}
class ViewController: UIViewController {
@IBOutlet weak var collectionView: UICollectionView!
override func viewDidLayoutSubviews() {
tremendous.viewDidLayoutSubviews()
if let flowLayout = collectionView.collectionViewLayout as? UICollectionViewFlowLayout {
flowLayout.itemSize = CGSize(
width: collectionView.bounds.width,
top: 120
)
}
}
}
extension ViewController: UICollectionViewDataSource {
func numberOfSections(
in collectionView: UICollectionView
) -> Int {
1
}
func collectionView(
_ collectionView: UICollectionView,
numberOfItemsInSection part: Int
) -> Int {
10
}
func collectionView(
_ collectionView: UICollectionView,
cellForItemAt indexPath: IndexPath
) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(
withReuseIdentifier: "MyCell",
for: indexPath
) as! MyCell
cell.textLabel.textual content = String(indexPath.row + 1)
return cell
}
}
extension ViewController: UICollectionViewDelegate {
func collectionView(
_ collectionView: UICollectionView,
didSelectItemAt indexPath: IndexPath
) {
print(indexPath.merchandise + 1)
}
}
In a nutshell, the information supply will present all of the required information about methods to populate the gathering view, and the delegate will deal with consumer occasions, equivalent to tapping on a cell. It’s best to have a transparent understanding concerning the information supply and delegate strategies, so be at liberty to play with them for a short while. ⌨️
The way to setup a UICollectionView primarily based display screen programmatically?
As you may need seen cells are the core parts of a group view. They’re derived from reusable views, because of this if in case you have an inventory of 1000 components, there received’t be a thousand cells created for each aspect, however only some that fills the dimensions of the display screen and whenever you scroll down the checklist these things are going to be reused to show your components. That is solely due to reminiscence issues, so not like UIScrollView the UICollectionView (and UITableView) class is a very sensible and environment friendly one, however that is additionally the explanation why you need to put together (reset the contents of) the cell each time earlier than you show your precise information. 😉
Initialization can also be dealt with by the system, but it surely’s price to say that in case you are working with Interface Builder, you need to do your customization contained in the awakeFromNib methodology, however in case you are utilizing code, init(body:) is your home.
import UIKit
class MyCell: UICollectionViewCell {
weak var textLabel: UILabel!
override init(body: CGRect) {
tremendous.init(body: body)
let textLabel = UILabel(body: .zero)
textLabel.translatesAutoresizingMaskIntoConstraints = false
contentView.addSubview(textLabel)
NSLayoutConstraint.activate([
textLabel.topAnchor.constraint(
equalTo: contentView.topAnchor
),
textLabel.bottomAnchor.constraint(
equalTo: contentView.bottomAnchor
),
textLabel.leadingAnchor.constraint(
equalTo: contentView.leadingAnchor
),
textLabel.trailingAnchor.constraint(
equalTo: contentView.trailingAnchor
),
])
self.textLabel = textLabel
contentView.backgroundColor = .lightGray
textLabel.textAlignment = .heart
}
required init?(coder aDecoder: NSCoder) {
tremendous.init(coder: aDecoder)
fatalError("Interface Builder isn't supported!")
}
override func awakeFromNib() {
tremendous.awakeFromNib()
fatalError("Interface Builder isn't supported!")
}
override func prepareForReuse() {
tremendous.prepareForReuse()
textLabel.textual content = nil
}
}
Subsequent we’ve got to implement the view controller which is chargeable for managing the gathering view, we’re not utilizing IB so we’ve got to create it manually by utilizing Auto Structure anchors – like for the textLabel within the cell – contained in the loadView methodology. After the view hierarchy is able to rock, we additionally set the information supply and delegate plus register our cell class for additional reuse. Observe that that is achieved mechanically by the system in case you are utilizing IB, however when you choose code you need to do it by calling the correct registration methodology. You possibly can register each nibs and courses.
import UIKit
class ViewController: UIViewController {
weak var collectionView: UICollectionView!
override func loadView() {
tremendous.loadView()
let collectionView = UICollectionView(
body: .zero,
collectionViewLayout: UICollectionViewFlowLayout()
)
collectionView.translatesAutoresizingMaskIntoConstraints = false
view.addSubview(collectionView)
NSLayoutConstraint.activate([
collectionView.topAnchor.constraint(
equalTo: view.topAnchor
),
collectionView.bottomAnchor.constraint(
equalTo: view.bottomAnchor
),
collectionView.leadingAnchor.constraint(
equalTo: view.leadingAnchor
),
collectionView.trailingAnchor.constraint(
equalTo: view.trailingAnchor
),
])
self.collectionView = collectionView
}
override func viewDidLoad() {
tremendous.viewDidLoad()
collectionView.backgroundColor = .white
collectionView.dataSource = self
collectionView.delegate = self
collectionView.register(
MyCell.self,
forCellWithReuseIdentifier: "MyCell"
)
}
}
extension ViewController: UICollectionViewDataSource {
func numberOfSections(
in collectionView: UICollectionView
) -> Int {
1
}
func collectionView(
_ collectionView: UICollectionView,
numberOfItemsInSection part: Int
) -> Int {
10
}
func collectionView(
_ collectionView: UICollectionView,
cellForItemAt indexPath: IndexPath
) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(
withReuseIdentifier: "MyCell",
for: indexPath
) as! MyCell
cell.textLabel.textual content = String(indexPath.row + 1)
return cell
}
}
extension ViewController: UICollectionViewDelegate {
func collectionView(
_ collectionView: UICollectionView,
didSelectItemAt indexPath: IndexPath
) {
print(indexPath.row + 1)
}
}
extension ViewController: UICollectionViewDelegateFlowLayout {
func collectionView(
_ collectionView: UICollectionView,
structure collectionViewLayout: UICollectionViewLayout,
sizeForItemAt indexPath: IndexPath
) -> CGSize {
.init(
width: collectionView.bounds.dimension.width - 16,
top: 120
)
}
func collectionView(
_ collectionView: UICollectionView,
structure collectionViewLayout: UICollectionViewLayout,
minimumLineSpacingForSectionAt part: Int
) -> CGFloat {
8
}
func collectionView(
_ collectionView: UICollectionView,
structure collectionViewLayout: UICollectionViewLayout,
minimumInteritemSpacingForSectionAt part: Int
) -> CGFloat {
0
}
func collectionView(
_ collectionView: UICollectionView,
structure collectionViewLayout: UICollectionViewLayout,
insetForSectionAt part: Int
) -> UIEdgeInsets {
.init(prime: 8, left: 8, backside: 8, proper: 8)
}
}
This time you need to pay some consideration on the circulation structure delegate strategies. You should utilize these strategies to supply metrics for the structure system. The circulation structure will show all of the cells primarily based on these numbers and sizes. sizeForItemAt is chargeable for the cell dimension, minimumInteritemSpacingForSectionAt is the horizontal padding, minimumLineSpacingForSectionAt is the vertical padding, and insetForSectionAt is for the margin of the gathering view part.
So on this part I’m going to each use storyboards, nibs and a few Swift code. That is my common method for a couple of causes. Though I like making constraints from code, most individuals choose visible editors, so all of the cells are created inside nibs. Why nibs? As a result of if in case you have a number of assortment views that is “virtually” the one good option to share cells between them.
You possibly can create part footers precisely the identical means as you do headers, in order that’s why this time I’m solely going to give attention to headers, as a result of actually you solely have to vary one phrase with a purpose to use footers. ⚽️
You simply must create two xib information, one for the cell and one for the header. Please word that you may use the very same assortment view cell to show content material within the part header, however it is a demo so let’s simply go along with two distinct objects. You don’t even must set the reuse identifier from IB, as a result of we’ve got to register our reusable views contained in the supply code, so simply set the cell class and join your retailers.
Cell and supplementary aspect registration is barely completely different for nibs.
let cellNib = UINib(nibName: "Cell", bundle: nil)
self.collectionView.register(
cellNib,
forCellWithReuseIdentifier: "Cell"
)
let sectionNib = UINib(nibName: "Part", bundle: nil)
self.collectionView.register(
sectionNib,
forSupplementaryViewOfKind: UICollectionView.elementKindSectionHeader,
withReuseIdentifier: "Part"
)
Implementing the information supply for the part header seems to be like this.
func collectionView(
_ collectionView: UICollectionView,
viewForSupplementaryElementOfKind sort: String,
at indexPath: IndexPath
) -> UICollectionReusableView {
guard sort == UICollectionView.elementKindSectionHeader else {
return UICollectionReusableView()
}
let view = collectionView.dequeueReusableSupplementaryView(
ofKind: sort,
withReuseIdentifier: "Part",
for: indexPath
) as! Part
view.textLabel.textual content = String(indexPath.part + 1)
return view
}
Offering the dimensions for the circulation structure delegate can also be fairly easy, nonetheless typically I don’t actually get the naming conventions by Apple. As soon as you need to change a form, and the opposite time there are precise strategies for particular sorts. 🤷♂️
func collectionView(
_ collectionView: UICollectionView,
structure collectionViewLayout: UICollectionViewLayout,
referenceSizeForHeaderInSection part: Int
) -> CGSize {
.init(
width: collectionView.bounds.dimension.width,
top: 64
)
}
Ranging from iOS9 part headers and footers could be pinned to the highest or backside of the seen bounds of the gathering view.
if let flowLayout = self.collectionView.collectionViewLayout as? UICollectionViewFlowLayout {
flowLayout.sectionHeadersPinToVisibleBounds = true
}
That’s it, now you understand how to construct primary layouts with assortment view.
What about complicated instances, like utilizing a number of sorts of cells in the identical assortment view? Issues can get fairly messy with index paths, in order that’s why I re-invented one thing higher primarily based on a method methods to construct superior consumer interfaces with assortment views showcased by Apple again at WWDC 2014.
My CollectionView primarily based UI framework
Now you recognize the fundamentals, so why don’t we get straight to the purpose? I’ll present you my finest follow of constructing nice consumer interfaces by utilizing my MVVM structure primarily based CollectionView micro framework.
CollectionView + ViewModel sample = ❤️ .
I’ll clarify the parts actual fast and after that you just’ll learn to use them to construct up the Apple music-ish structure that I used to be speaking about at first. 🎶
Grid system
The primary drawback with assortment views is the dimensions calculation. It’s important to present the dimensions (width & top) for every cell inside your assortment view.
- if all the pieces has a set dimension inside your assortment view, you possibly can simply set the dimensions properties on the circulation structure itself
- when you want dynamic sizes per merchandise, you possibly can implement the circulation structure delegate aka. UICollectionViewDelegateFlowLayout (why is the delegate phrase in the midst of the title???) and return the precise sizes for the structure system
- when you want much more management you possibly can create a brand new structure subclass derived from CollectionView(Movement)Structure and do all the dimensions calculations there
Thats good, however nonetheless you need to mess with index paths, trait collections, frames and plenty of extra with a purpose to have a easy 2, 4, n column structure that adapts on each gadget. That is the explanation why I’ve created a very primary grid system for dimension calculation. With my grid class you possibly can simply set the variety of columns and get again the dimensions for x quantity of columns, “identical to” in internet primarily based css grid methods. 🕸
Cell reuse
Registering and reusing cells ought to and could be automated in a kind protected method. You simply wish to use the cell, and also you shouldn’t care about reuse identifiers and cell registration in any respect. I’ve made a pair helper strategies with a purpose to make the progress extra nice. Reuse identifiers are derived from the title of the cell courses, so that you dont’t have to fret about anymore. It is a follow that a lot of the builders use.
View mannequin
view mannequin = cell (view) + information (mannequin)
Filling up “template” cell with actual information must be the duty of a view mannequin. That is the place MVVM comes into play. I’ve made a generic base view mannequin class, that you need to subclass. With the assistance of a protocol, you should use varied cells in a single assortment view with out going loopy of the row & part calculations and you may give attention to one easy process: connecting view with fashions. 😛
Part
part = header + footer + cells
I’m attempting to emphasise that you just don’t wish to mess with index paths, you simply wish to put your information collectively and that’s it. Prior to now I’ve struggled greater than sufficient with “pointless index path math”, so I’ve made the part object as a easy container to wrap headers, footers and all of the objects within the part. The outcome? Generic information supply class that can be utilized with a number of cells with none row or part index calculations. 👏👏👏
Supply
So with a purpose to make all of the issues I’ve talked about above work, I wanted to implement the gathering view delegate, information supply, and circulation structure delegate strategies. That’s how my supply class was born. Every thing is carried out right here, and I’m utilizing sections, view fashions the grid system to construct up assortment views. However hey, sufficient from this idea, let’s see it in follow. 👓
CollectionView framework instance utility
The way to make a any checklist or grid structure problem free? Properly, as a primary step simply add my CollectionView framework as a dependency. Don’t fear you received’t remorse it, plus it helps Xcode 11 already, so you should use the Swift Package deal Supervisor, straight from the file menu to combine this package deal.
Tip: simply add the @_exported import CollectionView line within the AppDelegate file, then you definately I don’t have to fret about importing the framework file-by-file.
Step 1. Make the cell.
This step is equivalent with the common setup, besides that your cell must be a subclass of my Cell class. Add your personal cell and do all the pieces as you’ll do usually.
import UIKit
class AlbumCell: Cell {
@IBOutlet weak var textLabel: UILabel!
@IBOutlet weak var detailTextLabel: UILabel!
@IBOutlet weak var imageView: UIImageView!
override func awakeFromNib() {
tremendous.awakeFromNib()
self.textLabel.font = UIFont.systemFont(ofSize: 12, weight: .daring)
self.textLabel.textColor = .black
self.detailTextLabel.font = UIFont.systemFont(ofSize: 12, weight: .daring)
self.detailTextLabel.textColor = .darkGray
self.imageView.layer.cornerRadius = 8
self.imageView.layer.masksToBounds = true
}
override func reset() {
tremendous.reset()
self.textLabel.textual content = nil
self.detailTextLabel.textual content = nil
self.imageView.picture = nil
}
}
Step 2. Make a mannequin
Simply choose a mannequin object. It may be something, however my method is to make a brand new struct or class with a Mannequin suffix. This fashion I do know that fashions are referencing the gathering view fashions inside my reusable parts folder.
import Basis
struct AlbumModel {
let artist: String
let title: String
let picture: String
}
Step 3. Make the view mannequin.
Now as a substitute of configuring the cell contained in the delegate, or in a configure methodology someplace, let’s make an actual view mannequin for the cell & the information mannequin that’s going to be represented by way of the view.
import UIKit
class AlbumViewModel: ViewModel {
override func updateView() {
self.view?.textLabel.textual content = self.mannequin.artist
self.view?.detailTextLabel.textual content = self.mannequin.title
self.view?.imageView.picture = UIImage(named: self.mannequin.picture)
}
override func dimension(grid: Grid) -> CGSize {
if
(self.collectionView.traitCollection.userInterfaceIdiom == .telephone &&
self.collectionView.traitCollection.verticalSizeClass == .compact) ||
self.collectionView?.traitCollection.userInterfaceIdiom == .pad
{
return grid.dimension(
for: self.collectionView,
ratio: 1.2,
objects: grid.columns / 4,
gaps: grid.columns - 1
)
}
if grid.columns == 1 {
return grid.dimension(for: self.collectionView, ratio: 1.1)
}
return grid.dimension(
for: self.collectionView,
ratio: 1.2,
objects: grid.columns / 2,
gaps: grid.columns - 1
)
}
}
Step 4. Setup your information supply.
Now, use your actual information and populate your assortment view utilizing the view fashions.
let grid = Grid(columns: 1, margin: UIEdgeInsets(all: 8))
self.collectionView.supply = .init(grid: grid, [
[
HeaderViewModel(.init(title: "Albums"))
AlbumViewModel(self.album)
],
])
self.collectionView.reloadData()
Step 5. 🍺🤘🏻🎸
Congratulations you’re achieved together with your first assortment view. With only a few strains of code you’ve got a ROCK SOLID code that may assist you to out in a lot of the conditions! 😎
That is simply the tip of the iceberg! 🚢
What if we make a cell that comprises a group view and we use the identical methodology like above? A group view containing a group view… UICollectionViewception!!! 😂
It’s utterly attainable, and very easy to do, the information that feeds the view mannequin shall be a group view supply object, and also you’re achieved. Easy, magical and tremendous good to implement, additionally included within the instance app.
Sections with artists & round photos
A number of sections? No drawback, round photos? That’s additionally a bit of cake, when you had learn my earlier tutorial about round assortment view cells, you’ll know methods to do it, however please take a look at the supply code from GitLab and see it for your self in motion.
Callbacks and actions
Person occasions could be dealt with very simple, as a result of view fashions can have delegates or callback blocks, it solely is dependent upon you which of them one you favor. The instance comprises an onSelect handler, which is tremendous good and built-in to the framework. 😎
Dynamic cell sizing re-imagined
I additionally had a tutorial about assortment view self sizing cell help, however to be sincere I’m not an enormous fan of Apple’s official methodology. After I’ve made the grid system and began utilizing view fashions, it was less difficult to calculate cell heights on my own, with about 2 strains of additional code. I consider that’s price it, as a result of self sizing cells are somewhat buggy if it involves auto rotation.
Rotation help, adaptivity
Don’t fear about that an excessive amount of, you possibly can merely change the grid or verify trait collections contained in the view mannequin in order for you. I’d say virtually all the pieces could be achieved proper out of the field. My assortment view micro framework is only a light-weight wrapper across the official assortment view APIs. That’s the fantastic thing about it, be at liberty to do no matter you need and use it in a means that YOU personally choose. 📦
Now go, seize the pattern code and hearken to some steel! 🤘🏻
What if I informed you… another factor: SwiftUI
These are some unique quotes of mine again from April, 2018:
In case you like this methodology that’s cool, however what if I informed you that there’s extra? Do you wish to use the identical sample in every single place? I imply on iOS, tvOS, macOS and even watchOS. Performed deal! I’ve created all the pieces contained in the CoreKit framework. UITableViews, WKInterfaceTables are supported as nicely.
Properly, I’m a visionary, however SwiftUI was late 1 12 months, it arrived in 2019:
I actually consider that Apple this 12 months will method the following technology UIKit / AppKit / UXKit frameworks (written in Swift after all) considerably like this. I’m not speaking concerning the view mannequin sample, however about the identical API on each platform pondering. Anyway, who is aware of this for sue, we’ll see… #wwdc18 🤔
If somebody from Apple reads this, please clarify me why the hell is SwiftUI nonetheless an abstraction layer above UIKit/ AppKit as a substitute of a refactored AppleKit UI framework that lastly unifies each single API? For actual, why? Nonetheless don’t get it. 🤷♂️
Anyway, we’re getting in to the identical route guys, year-by-year I delete increasingly more self-written “Third-party” code, so that you’re doing nice progress there! 🍎
