[英]Swift - Paging UICollectionView by cell while keeping the cell horizontally centered
First, not sure if the title is correct or offers the best description but I'm not sure what else to use.首先,不确定标题是否正确或提供了最好的描述,但我不确定还可以使用什么。
So, i'm working on an app and I reached a section where I got stuck while implementing the UI.所以,我正在开发一个应用程序,但我在实现 UI 时遇到了卡住的部分。 Basically, I have a VC (image below) that can segue to its self based on the info I get from a JSON file.
基本上,我有一个 VC(下图),它可以根据我从 JSON 文件中获得的信息进行自我定位。
The thing is I need to have a carousel-like menu in the upper side with an undefined number of cells (again, depends on what I get from the JSON file).问题是我需要在上侧有一个类似轮播的菜单,其中包含未定义数量的单元格(同样,取决于我从 JSON 文件中获得的内容)。 I decided to go for a UICollectionView for this and I managed to implement the basics without any problem.
我决定为此使用 UICollectionView 并且我设法毫无问题地实现了基础知识。
But here is the part where I got stuck:但这是我卡住的部分:
I tried finding something similar but maybe I'm not looking for the right thing because all I could find was Paging UICollectionView by cells, not screen我试图找到类似的东西,但也许我没有在寻找正确的东西,因为我能找到的只是按单元格而不是屏幕分页 UICollectionView
Also, to be honest I've never seen an app / UICollectionView with this behaviour.另外,老实说,我从未见过具有这种行为的应用程序/ UICollectionView。
I posted parts of the code below but it's not really gonna help much since it's just standard UICollectionView methods.我在下面发布了部分代码,但它并没有多大帮助,因为它只是标准的 UICollectionView 方法。
Any suggestions?有什么建议?
class PreSignupDataVC : UIViewController, UICollectionViewDelegateFlowLayout, UICollectionViewDataSource, UIPickerViewDelegate, UIPickerViewDataSource
@IBOutlet weak var cvQuestions: UICollectionView!
var questionCell : PreSignupDataQuestionCellVC!
var screenData : Array<PreSignupScreenData> = Array<PreSignupScreenData>()
var pvDataSource : [String] = []
var numberOfComponents : Int = 0
var numberOfRowsInComponent : Int = 0
var currentScreen : Int = 1
var selectedType : Int?
var selectedCell : Int = 0
var initialLastCellInsetPoint : CGFloat = 0.0
override func viewDidLoad()
{
super.viewDidLoad()
print("PreSignupDataVC > viewDidLoad")
initialLastCellInsetPoint = (self.view.frame.width - 170)/2
screenData = DataSingleton.sharedInstance.returnPreSignUpUIArray()[selectedType!].screenData
numberOfComponents = screenData[currentScreen - 1].controls[0].numberOfComponents!
numberOfRowsInComponent = screenData[currentScreen - 1].controls[0].controlDataSource.count
pvDataSource = screenData[currentScreen - 1].controls[0].controlDataSource
cvQuestions.register(UINib(nibName: "PreSignupDataQuestionCell",
bundle: nil),
forCellWithReuseIdentifier: "PreSignupDataQuestionCellVC")
}
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int
{
print("PreSignupDataVC > collectionView > numberOfItemsInSection")
return screenData[currentScreen - 1].controls.count
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell
{
print("PreSignupDataVC > collectionView > cellForItemAt")
questionCell = (cvQuestions.dequeueReusableCell(withReuseIdentifier: "PreSignupDataQuestionCellVC",
for: indexPath) as? PreSignupDataQuestionCellVC)!
questionCell.vQuestionCellCellContainer.layer.cornerRadius = 8.0
questionCell.lblQuestion.text = screenData[currentScreen - 1].controls[indexPath.row].cellTitle
questionCell.ivQuestionCellImage.image = UIImage(named: screenData[currentScreen - 1].controls[indexPath.row].cellUnselectedIcon!)
return questionCell
}
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath)
{
print("PreSignupDataVC > collectionView > didSelectItemAt")
numberOfComponents = screenData[currentScreen - 1].controls[indexPath.row].numberOfComponents!
numberOfRowsInComponent = screenData[currentScreen - 1].controls[indexPath.row].controlDataSource.count
pvDataSource = screenData[currentScreen - 1].controls[indexPath.row].controlDataSource
selectedCell = indexPath.row
pvData.reloadAllComponents()
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAt section: Int) -> UIEdgeInsets
{
print("PreSignupDataVC > collectionView > insetForSectionAt")
return UIEdgeInsets(top: 0.0, left: initialLastCellInsetPoint, bottom: 00.0, right: initialLastCellInsetPoint)
}
UICollectionViewCompositionalLayout
(requires iOS 13)UICollectionViewCompositionalLayout
(需要 iOS 13) Since iOS 13, you can use UICollectionViewCompositionalLayout
and set NSCollectionLayoutSection
's orthogonalScrollingBehavior
property to .groupPagingCentered
in order to have a centered horizontal carousel-like layout.从 iOS 13 开始,您可以使用
UICollectionViewCompositionalLayout
并将NSCollectionLayoutSection
的orthogonalScrollingBehavior
.groupPagingCentered
属性设置为.groupPagingCentered
以获得居中的水平轮播式布局。
The following Swift 5.1 sample code shows a possible implementation of UICollectionViewCompositionalLayout
in order to have the layout you want:以下 Swift 5.1 示例代码显示了
UICollectionViewCompositionalLayout
的可能实现,以便获得您想要的布局:
CollectionView.swift CollectionView.swift
import UIKit
class CollectionView: UICollectionView {
override var safeAreaInsets: UIEdgeInsets {
return UIEdgeInsets(top: super.safeAreaInsets.top, left: 0, bottom: super.safeAreaInsets.bottom, right: 0)
}
}
ViewController.swift视图控制器.swift
import UIKit
class ViewController: UIViewController {
var collectionView: CollectionView!
var dataSource: UICollectionViewDiffableDataSource<Int, Int>!
override func viewDidLoad() {
super.viewDidLoad()
navigationItem.title = "Collection view"
// Compositional layout
let layout = UICollectionViewCompositionalLayout(sectionProvider: {
(sectionIndex: Int, layoutEnvironment: NSCollectionLayoutEnvironment) -> NSCollectionLayoutSection? in
let itemSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1), heightDimension: .fractionalHeight(1))
let item = NSCollectionLayoutItem(layoutSize: itemSize)
item.contentInsets = NSDirectionalEdgeInsets(top: 5, leading: 5, bottom: 5, trailing: 5)
let groupSize = NSCollectionLayoutSize(widthDimension: .fractionalHeight(1), heightDimension: .fractionalHeight(1))
let group = NSCollectionLayoutGroup.horizontal(layoutSize: groupSize, subitems: [item])
let section = NSCollectionLayoutSection(group: group)
section.orthogonalScrollingBehavior = UICollectionLayoutSectionOrthogonalScrollingBehavior.groupPagingCentered
return section
})
// Set collection view
collectionView = CollectionView(frame: .zero, collectionViewLayout: layout)
collectionView.backgroundColor = .systemGroupedBackground
collectionView.showsHorizontalScrollIndicator = false
collectionView.register(Cell.self, forCellWithReuseIdentifier: "Cell")
// View layout
view.addSubview(collectionView)
collectionView.translatesAutoresizingMaskIntoConstraints = false
collectionView.heightAnchor.constraint(equalToConstant: 160).isActive = true
collectionView.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true
collectionView.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
collectionView.trailingAnchor.constraint(equalTo: view.trailingAnchor).isActive = true
// Collection view diffable data source
dataSource = UICollectionViewDiffableDataSource<Int, Int>(collectionView: collectionView, cellProvider: {
(collectionView: UICollectionView, indexPath: IndexPath, identifier: Int) -> UICollectionViewCell? in
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath) as! Cell
return cell
})
var snapshot = NSDiffableDataSourceSnapshot<Int, Int>()
snapshot.appendSections([0])
snapshot.appendItems(Array(0 ..< 5))
dataSource.apply(snapshot, animatingDifferences: false)
}
}
Cell.swift Cell.swift
import UIKit
class Cell: UICollectionViewCell {
override init(frame: CGRect) {
super.init(frame: frame)
contentView.backgroundColor = .orange
}
required init?(coder: NSCoder) {
fatalError("not implemnted")
}
}
UICollectionViewFlowLayout
UICollectionViewFlowLayout
If you're targeting a lower version of iOS than iOS 13, you can subclass UICollectionViewFlowLayout
, compute the horizontal insets in prepare()
and implement targetContentOffset(forProposedContentOffset:withScrollingVelocity:)
in order to force the cell to be centered after user scroll.如果您的目标是低于 iOS 13 的 iOS 版本,您可以
UICollectionViewFlowLayout
,在prepare()
计算水平插入并实现targetContentOffset(forProposedContentOffset:withScrollingVelocity:)
以强制单元格在用户滚动后居中。
The following Swift 5.1 sample code shows how to implement the subclass of UICollectionViewFlowLayout
:以下 Swift 5.1 示例代码展示了如何实现
UICollectionViewFlowLayout
的子类:
ViewController.swift视图控制器.swift
import UIKit
class ViewController: UIViewController {
let flowLayout = PaggedFlowLayout()
override func viewDidLoad() {
super.viewDidLoad()
navigationItem.title = "Collection view"
let collectionView = UICollectionView(frame: .zero, collectionViewLayout: flowLayout)
collectionView.backgroundColor = .systemGroupedBackground
collectionView.showsHorizontalScrollIndicator = false
collectionView.decelerationRate = .fast
collectionView.dataSource = self
collectionView.contentInsetAdjustmentBehavior = .never
collectionView.register(Cell.self, forCellWithReuseIdentifier: "Cell")
view.addSubview(collectionView)
collectionView.translatesAutoresizingMaskIntoConstraints = false
collectionView.heightAnchor.constraint(equalToConstant: 160).isActive = true
collectionView.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true
collectionView.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
collectionView.trailingAnchor.constraint(equalTo: view.trailingAnchor).isActive = true
}
}
extension ViewController: UICollectionViewDataSource {
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return 9
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath) as! Cell
return cell
}
}
PaggedFlowLayout.swift PaggedFlowLayout.swift
import UIKit
class PaggedFlowLayout: UICollectionViewFlowLayout {
override init() {
super.init()
scrollDirection = .horizontal
minimumLineSpacing = 5
minimumInteritemSpacing = 0
sectionInset = UIEdgeInsets(top: 5, left: 5, bottom: 5, right: 5)
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
override func prepare() {
super.prepare()
guard let collectionView = collectionView else { fatalError() }
// itemSize
let itemHeight = collectionView.bounds.height - sectionInset.top - sectionInset.bottom
itemSize = CGSize(width: itemHeight, height: itemHeight)
// horizontal insets
let horizontalInsets = (collectionView.bounds.width - itemSize.width) / 2
sectionInset.left = horizontalInsets
sectionInset.right = horizontalInsets
}
/*
Add some snapping behaviour to center the cell after scrolling.
Source: https://stackoverflow.com/a/14291208/1966109
*/
override func targetContentOffset(forProposedContentOffset proposedContentOffset: CGPoint, withScrollingVelocity velocity: CGPoint) -> CGPoint {
guard let collectionView = collectionView else { return .zero }
var proposedContentOffset = proposedContentOffset
var offsetAdjustment = CGFloat.greatestFiniteMagnitude
let horizontalCenter = proposedContentOffset.x + collectionView.bounds.size.width / 2
let targetRect = CGRect(x: proposedContentOffset.x, y: 0, width: collectionView.bounds.size.width, height: collectionView.bounds.size.height)
guard let layoutAttributesArray = super.layoutAttributesForElements(in: targetRect) else { return .zero }
for layoutAttributes in layoutAttributesArray {
let itemHorizontalCenter = layoutAttributes.center.x
if abs(itemHorizontalCenter - horizontalCenter) < abs(offsetAdjustment) {
offsetAdjustment = itemHorizontalCenter - horizontalCenter
}
}
var nextOffset = proposedContentOffset.x + offsetAdjustment
let snapStep = itemSize.width + minimumLineSpacing
func isValidOffset(_ offset: CGFloat) -> Bool {
let minContentOffset = -collectionView.contentInset.left
let maxContentOffset = collectionView.contentInset.left + collectionView.contentSize.width - itemSize.width
return offset >= minContentOffset && offset <= maxContentOffset
}
repeat {
proposedContentOffset.x = nextOffset
let deltaX = proposedContentOffset.x - collectionView.contentOffset.x
let velX = velocity.x
if deltaX.sign.rawValue * velX.sign.rawValue != -1 {
break
}
nextOffset += CGFloat(velocity.x.sign.rawValue) * snapStep
} while isValidOffset(nextOffset)
return proposedContentOffset
}
}
Cell.swift Cell.swift
import UIKit
class Cell: UICollectionViewCell {
override init(frame: CGRect) {
super.init(frame: frame)
contentView.backgroundColor = .orange
}
required init?(coder: NSCoder) {
fatalError("not implemnted")
}
}
Display on iPhone 11 Pro Max: iPhone 11 Pro Max 上的显示:
You can use
insetForSectionAtIndex
to add spacing at first and last cell
您可以使用
insetForSectionAtIndex
在第一个和最后一个单元格添加间距
UPDATE
更新
You can use scroll view.您可以使用滚动视图。
First: add leading and trailing to scroll view:首先:添加前导和尾随滚动视图:
Second: scrollView.clipsToBounds = false
第二:
scrollView.clipsToBounds = false
Third: add view to scroll view第三:添加视图滚动视图
func setupScrollView() {
DispatchQueue.main.async {
self.scrollView.layoutIfNeeded() // in order to get correct frame
let numberItem = 6
let spaceBetweenView: CGFloat = 20
let firstAndLastSpace: CGFloat = spaceBetweenView / 2
let width = self.scrollView.frame.size.width
let height = self.scrollView.frame.size.height
let numberOfView: CGFloat = CGFloat(numberItem)
let scrollViewContentSizeWidth = numberOfView * width
self.scrollView.contentSize = CGSize(width: scrollViewContentSizeWidth, height: height)
for index in 0..<numberItem {
let xCoordinate = (CGFloat(index) * (width)) + firstAndLastSpace
let viewFrame = CGRect(x: xCoordinate, y: 0, width: width - spaceBetweenView, height: height)
let view = UIView()
view.backgroundColor = .red
view.frame = viewFrame
self.scrollView.addSubview(view)
}
}
}
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