Anatomy of the UICollectionView class
For those who’re not aware of UICollectionView, I would counsel to get aware of this class instantly. They’re the essential constructing blocks for a lot of apps offered by Apple and different third occasion builders. It is like UITableView on steroids. Here’s a fast intro about work with them by IB and Swift code. 💻
You might need seen that I’ve a love for steel music. On this tutorial we will construct an Apple Music catalog like look from floor zero utilizing solely the mighty UICollectionView class. Headers, horizontal and vertical scrolling, round photos, so mainly virtually the whole lot that you will ever must construct nice consumer interfaces. 🤘🏻
The way to make a UICollectionView utilizing Interface Builder (IB) in Xcode?
The quick & sincere reply: you should not use IB!
For those who nonetheless need to use IB, here’s a actual fast tutorial for completely newcomers:
The principle steps of making your first UICollectionView based mostly 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 format 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,
peak: 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 info supply will present all of the required information about populate the gathering view, and the delegate will deal with consumer occasions, akin to tapping on a cell. It is best to have a transparent understanding in regards to the information supply and delegate strategies, so be happy to play with them for a short time. ⌨️
The way to setup a UICollectionView based mostly display screen programmatically?
As you might need seen cells are the core parts of a group view. They’re derived from reusable views, which means when you’ve got an inventory of 1000 parts, there will not be a thousand cells created for each component, however only some that fills the dimensions of the display screen and while you scroll down the listing these things are going to be reused to show your parts. That is solely due to reminiscence issues, so not like UIScrollView the UICollectionView (and UITableView) class is a very good and environment friendly one, however that is additionally the rationale why it’s important to put together (reset the contents of) the cell each time earlier than you show your precise information. 😉
Initialization can be dealt with by the system, but it surely’s value to say that in case you are working with Interface Builder, it is best to do your customization contained in the awakeFromNib technique, however in case you are utilizing code, init(body:) is your house.
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 shouldn't be supported!")
}
override func awakeFromNib() {
tremendous.awakeFromNib()
fatalError("Interface Builder shouldn't be supported!")
}
override func prepareForReuse() {
tremendous.prepareForReuse()
textLabel.textual content = nil
}
}Subsequent we now have to implement the view controller which is liable for managing the gathering view, we’re not utilizing IB so we now have to create it manually by utilizing Auto Format anchors – like for the textLabel within the cell – contained in the loadView technique. After the view hierarchy is able to rock, we additionally set the info supply and delegate plus register our cell class for additional reuse. Notice that that is performed routinely by the system in case you are utilizing IB, however when you desire code it’s important to do it by calling the correct registration technique. You may register each nibs and lessons.
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,
format collectionViewLayout: UICollectionViewLayout,
sizeForItemAt indexPath: IndexPath
) -> CGSize {
.init(
width: collectionView.bounds.dimension.width - 16,
peak: 120
)
}
func collectionView(
_ collectionView: UICollectionView,
format collectionViewLayout: UICollectionViewLayout,
minimumLineSpacingForSectionAt part: Int
) -> CGFloat {
8
}
func collectionView(
_ collectionView: UICollectionView,
format collectionViewLayout: UICollectionViewLayout,
minimumInteritemSpacingForSectionAt part: Int
) -> CGFloat {
0
}
func collectionView(
_ collectionView: UICollectionView,
format collectionViewLayout: UICollectionViewLayout,
insetForSectionAt part: Int
) -> UIEdgeInsets {
.init(prime: 8, left: 8, backside: 8, proper: 8)
}
}This time it is best to pay some consideration on the move format delegate strategies. You should utilize these strategies to offer metrics for the format system. The move format will show all of the cells based mostly on these numbers and sizes. sizeForItemAt is liable 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.
Utilizing supplementary parts (part headers and footers)
So on this part I will each use storyboards, nibs and a few Swift code. That is my standard strategy for just a few causes. Though I really like making constraints from code, most individuals desire visible editors, so all of the cells are created inside nibs. Why nibs? As a result of when you’ve got a number of assortment views that is “virtually” the one good method to share cells between them.
You may create part footers precisely the identical approach as you do headers, in order that’s why this time I am solely going to deal with headers, as a result of actually you solely have to vary one phrase with a purpose to use footers. ⚽️
You simply need to create two xib recordsdata, one for the cell and one for the header. Please notice that you might 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 do not even need to set the reuse identifier from IB, as a result of we now have to register our reusable views contained in the supply code, so simply set the cell class and join your shops.
Cell and supplementary component 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 info supply for the part header seems to be like this.
func collectionView(
_ collectionView: UICollectionView,
viewForSupplementaryElementOfKind form: String,
at indexPath: IndexPath
) -> UICollectionReusableView {
guard form == UICollectionView.elementKindSectionHeader else {
return UICollectionReusableView()
}
let view = collectionView.dequeueReusableSupplementaryView(
ofKind: form,
withReuseIdentifier: "Part",
for: indexPath
) as! Part
view.textLabel.textual content = String(indexPath.part + 1)
return view
}Offering the dimensions for the move format delegate can be fairly simple, nevertheless generally I do not actually get the naming conventions by Apple. As soon as it’s important to change a sort, and the opposite time there are actual strategies for particular sorts. 🤷♂️
func collectionView(
_ collectionView: UICollectionView,
format collectionViewLayout: UICollectionViewLayout,
referenceSizeForHeaderInSection part: Int
) -> CGSize {
.init(
width: collectionView.bounds.dimension.width,
peak: 64
)
}Ranging from iOS9 part headers and footers may 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 is 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 based mostly on a method construct superior consumer interfaces with assortment views showcased by Apple again at WWDC 2014.
My CollectionView based mostly UI framework
Now you already know the fundamentals, so why do not we get straight to the purpose? I will present you my finest observe of constructing nice consumer interfaces by utilizing my MVVM structure based mostly CollectionView micro framework.
CollectionView + ViewModel sample = ❤️ .
I will clarify the parts actual fast and after that you will discover ways to use them to construct up the Apple music-ish format that I used to be speaking about at first. 🎶
Grid system
The primary drawback with assortment views is the dimensions calculation. You must present the dimensions (width & peak) for every cell inside your assortment view.
- if the whole lot has a set dimension inside your assortment view, you possibly can simply set the dimensions properties on the move format itself
- when you want dynamic sizes per merchandise, you possibly can implement the move format delegate aka. UICollectionViewDelegateFlowLayout (why is the delegate phrase in the midst of the identify???) and return the precise sizes for the format system
- when you want much more management you possibly can create a brand new format subclass derived from CollectionView(Stream)Format and do all the dimensions calculations there
Thats good, however nonetheless it’s important to mess with index paths, trait collections, frames and plenty of extra with a purpose to have a easy 2, 4, n column format that adapts on each gadget. That is the rationale 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, “similar to” in net based mostly css grid techniques. 🕸
Cell reuse
Registering and reusing cells ought to and may be automated in a sort protected method. You simply need to use the cell, and also you should not 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 identify of the cell lessons, so that you dont’t have to fret about anymore. It is a observe that a lot of the builders use.
View mannequin
view mannequin = cell (view) + information (mannequin)
Filling up “template” cell with actual information needs to 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 it is best to subclass. With the assistance of a protocol, you should utilize varied cells in a single assortment view with out going loopy of the row & part calculations and you may deal with one easy job: connecting view with fashions. 😛
Part
part = header + footer + cells
I am attempting to emphasise that you do not need to mess with index paths, you simply need to put your information collectively and that is 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 inside the part. The end result? 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 move format delegate strategies. That is how my supply class was born. Every little thing is applied right here, and I am utilizing sections, view fashions the grid system to construct up assortment views. However hey, sufficient from this principle, let’s examine it in observe. 👓
CollectionView framework instance software
The way to make a any listing or grid format trouble free? Properly, as a primary step simply add my CollectionView framework as a dependency. Don’t fret you will not remorse it, plus it helps Xcode 11 already, so you should utilize 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 haven’t got 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 need to be a subclass of my Cell class. Add your personal cell and do the whole lot as you’d 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 decide a mannequin object. It may be something, however my strategy 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 identify: String
let picture: String
}Step 3. Make the view mannequin.
Now as an alternative of configuring the cell contained in the delegate, or in a configure technique someplace, let’s make an actual view mannequin for the cell & the info mannequin that is going to be represented by way of the view.
import UIKit
class AlbumViewModel: ViewModel<AlbumCell, AlbumModel> {
override func updateView() {
self.view?.textLabel.textual content = self.mannequin.artist
self.view?.detailTextLabel.textual content = self.mannequin.identify
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 are performed together with your first assortment view. With just some strains of code you have got a ROCK SOLID code that may assist you out in a lot of the conditions! 😎
That is simply the tip of the iceberg! 🚢
Horizontal scrolling inside vertical scrolling
What if we make a cell that accommodates a group view and we use the identical technique like above? A group view containing a group view… UICollectionViewception!!! 😂
It is utterly attainable, and very easy to do, the info that feeds the view mannequin can be a group view supply object, and also you’re performed. 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 is additionally a bit of cake, when you had learn my earlier tutorial about round assortment view cells, you will know do it, however please try the supply code from GitLab and see it for your self in motion.
Callbacks and actions
Consumer occasions may be dealt with very straightforward, as a result of view fashions can have delegates or callback blocks, it solely will depend on you which of them one you favor. The instance accommodates 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 assist, however to be sincere I am not a giant fan of Apple’s official technique. After I’ve made the grid system and began utilizing view fashions, it was easier to calculate cell heights on my own, with about 2 strains of additional code. I imagine that is value it, as a result of self sizing cells are a bit buggy if it involves auto rotation.
Rotation assist, adaptivity
Don’t fret about that an excessive amount of, you possibly can merely change the grid or examine trait collections contained in the view mannequin in order for you. I would say virtually the whole lot may be performed proper out of the field. My assortment view micro framework is only a light-weight wrapper across the official assortment view APIs. That is the great thing about it, be happy to do no matter you need and use it in a approach that YOU personally desire. 📦
Now go, seize the pattern code and hearken to some steel! 🤘🏻
What if I informed you… yet another factor: SwiftUI
These are some authentic quotes of mine again from April, 2018:
For those who like this technique that is cool, however what if I informed you that there’s extra? Do you need to use the identical sample in every single place? I imply on iOS, tvOS, macOS and even watchOS. Performed deal! I’ve created the whole lot contained in the CoreKit framework. UITableViews, WKInterfaceTables are supported as nicely.
Properly, I am a visionary, however SwiftUI was late 1 yr, it arrived in 2019:
I actually imagine that Apple this yr will strategy the subsequent technology UIKit / AppKit / UXKit frameworks (written in Swift in fact) considerably like this. I am not speaking in regards to the view mannequin sample, however about the identical API on each platform considering. 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 an alternative of a refactored AppleKit UI framework that lastly unifies each single API? For actual, why? Nonetheless do not get it. 🤷♂️
Anyway, we’re moving into to the identical course guys, year-by-year I delete increasingly self-written “Third-party” code, so that you’re doing nice progress there! 🍎
