difficulty dealing with the reusability of the collection view cell. - ios

Question

I am trying to create a seating plan using the collection view. In that each seat will have a specific number that means that each cell will have a label that displays the seat number. I am using custom collection view layout to create a seat map and the seat map is 2 way scrollable. Every thing goes well untill the seat map gets scrolled. once the seat map is scrolled the values of the seat numbers are being changed. I know that it is because of the reusability of the collection view cells but i can't find a way out. I tried to search for answer in stack but nothing is working for me. please help..
here is my view controller:
class ViewController: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource {
#IBOutlet weak var collectionView: UICollectionView!
var seatNo = 0
override func viewDidLoad() {
super.viewDidLoad()
collectionView.dataSource = self
collectionView.delegate = self
}
// func for number of section in collection view
func numberOfSections(in collectionView: UICollectionView) -> Int {
return 10
}
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return 15
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "CollectionViewCell", for: indexPath) as! CollectionViewCell
if indexPath.row == 0 {
seatNo = 1
}
cell.assignSeat(seat: seatNo)
seatNo += 1
cell.seatNumber.text = "\(cell.seat ?? 0)"
return cell
}
}
and here is my collection view cell :
class CollectionViewCell: UICollectionViewCell {
#IBOutlet weak var seatNumber: UILabel!
var seat: Int?
override func prepareForReuse() {
seatNumber.text = ""
seat = 0
}
func assignSeat(seat: Int) {
self.seat = seat
}
}
and if needed here is the code for the custom Collection View Layout:
class CustomCollectionLayout: UICollectionViewLayout {
// var for cell height
var CELL_HEIGHT: Double!
//Variable for cell width
var CELL_WIDTH: Double!
// Variable for the status bar height
let STATUS_BAR = UIApplication.shared.statusBarFrame.height
// Array to store the cell attributes
var cache = [UICollectionViewLayoutAttributes]()
//variable to define the content size
var contentSize = CGSize.zero
// another variable to store the cell atributes
var cellAttrsDictionary = [UICollectionViewLayoutAttributes]()
// variable to store the cell padding
var cellPadding: Double!
// func that defines the collection view content size
override var collectionViewContentSize: CGSize{
return self.contentSize
}
// func to prepare the collection view
// how the cells are to be mapped is defined in this function
override func prepare() {
// assigning the values to the variables
CELL_HEIGHT = 44
CELL_WIDTH = 44
cellPadding = 2
// Cycle through each section of the data source.
if collectionView?.isDragging == false{
if collectionView!.numberOfSections > 0 {
for section in 0...collectionView!.numberOfSections-1 {
// Cycle through each item in the section.
if collectionView!.numberOfItems(inSection: section) > 0 {
for item in 0...collectionView!.numberOfItems(inSection: section)-1 {
// storing the index of the current cell
let cellIndex = NSIndexPath(item: item, section: section)
// defining the x and y coordinates for the other cells
let xPos = Double(item) * CELL_WIDTH
let yPos = Double(section) * CELL_HEIGHT
//creating the frame for the cell
let frame = CGRect(x: xPos, y: yPos, width: CELL_WIDTH, height: CELL_HEIGHT)
//providing the padding
let cellFinalAttribute = frame.insetBy(dx:CGFloat(cellPadding) ,dy:CGFloat(cellPadding))
//storing the cellattributes in the array
let cellAttributes = UICollectionViewLayoutAttributes(forCellWith: cellIndex as IndexPath)
cellAttributes.frame = cellFinalAttribute
cellAttrsDictionary.append(cellAttributes)
}
}
}
}
// Update content size.
let contentWidth = Double(collectionView!.numberOfItems(inSection: 0)) * CELL_WIDTH
let contentHeight = Double(collectionView!.numberOfSections) * CELL_HEIGHT
self.contentSize = CGSize(width: contentWidth, height: contentHeight)
}
}
// func that returns the cell attributes for the elements that are visible in the screen
override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
// Create an array to hold all elements found in our current view.
var attributesInRect = [UICollectionViewLayoutAttributes]()
// Check each element to see if it should be returned.
for cellAttributes in cellAttrsDictionary {
if rect.intersects(cellAttributes.frame) {
attributesInRect.append(cellAttributes)
}
}
// Return list of elements.
return attributesInRect
}
//func that returns the cell attributes for the indexpath
override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
return cellAttrsDictionary[indexPath.row]
}
//this func call the prepare func if the user scrolls if returned true
override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
return false
}
}

Answer 1

Rather than using an array, why not say
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "CollectionViewCell", for: indexPath) as! CollectionViewCell
let seatNo = (indexPath.row + 1) + (indexPath.section * 15)
cell.assignSeat(seat: seatNo)
cell.seatNumber.text = "\(cell.seat ?? 0)"
return cell
}
I haven't ran this code but the idea is to use
indexPath.row + 1
to get the seats position in its row.
then we can use
indexPath.section * 15 // (number of seats per row should be declared static)
to get the count of seats in the previous rows to this one. in the first row the section will be 0 so won't add anything but subsequent rows will be added correctly
I highly advise declaring the 15 and 10 at the top of your file to avoid magic numbers