I have given constraints for image and label like this

我给出了这样的形象和标签的约束

Image constraints. Label Constraints

图像约束。标签约束

code: with this code i am able to get selectedNamesArray but unable to change cell colour. where am i wrong? is there anything wrong in storyboard constraints so that cell BG is not changing? or any other coding mistake? could anyone please explain the issue and the solution for cell background change

代码：使用此代码，我可以选择名称数组，但不能更改单元格颜色。我哪里错了？故事板约束有什么问题吗？这样单元格BG就不会改变？或任何其他编码错误？有没有人能解释一下单元格背景变化的问题和解决办法

class TestCollectionCell: UICollectionViewCell{
@IBOutlet weak var roundImg: UIImageView!
@IBOutlet weak var titleLbl: UILabel!

override func awakeFromNib() {
    super.awakeFromNib()
}

override func layoutSubviews() {
    super.layoutSubviews()
    roundImg.layer.cornerRadius = roundImg.frame.width / 2
    roundImg.contentMode = .scaleToFill
    roundImg.clipsToBounds = true
}
}


override func viewDidLoad() {
super.viewDidLoad()

collectionView.delegate = self
collectionView.dataSource = self

let layOut = UICollectionViewFlowLayout()
layOut.scrollDirection = .vertical

collectionView.collectionViewLayout = layOut
collectionView.allowsMultipleSelection = true
GenericCodableServicecall()
}

var cvWidth: CGFloat = -1.0

override func viewDidLayoutSubviews() {
super.viewDidLayoutSubviews()
if cvWidth != collectionView.frame.size.width {
    cvWidth = collectionView.frame.size.width
    if let fl = collectionView.collectionViewLayout as? UICollectionViewFlowLayout {

        let nColumns: Int = 4
        
        let sideSpace: CGFloat = fl.sectionInset.left + fl.sectionInset.right
        
        let totalEmptyspace: CGFloat = sideSpace + (CGFloat(nColumns) * 3.0)
        
        let w = (cvWidth - totalEmptyspace) / CGFloat(nColumns)
        fl.itemSize = .init(width: w, height: w)

        fl.minimumInteritemSpacing = 0.0
    }
}
}

func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
namesArray.count
}

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "TestCollectionCell", for: indexPath) as! TestCollectionCell
cell.layoutIfNeeded()
cell.titleLbl.text = namesArray[indexPath.row]
return cell
}

func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath)     {

print("in select..")

let cell = collectionView.cellForItem(at: indexPath) as! TestCollectionCell
let selectedName = namesArray[indexPath.row]
if let inx = selectedNamesArray.firstIndex(of: selectedName){
    selectedNamesArray.remove(at: inx)
    cell.backgroundColor = UIColor.red
}
else{
    selectedNamesArray.append(selectedName)
    cell.backgroundColor = UIColor.yellow
}
print(selectedNamesArray)
}

unable to change cell background when i select/deselect always showing green background only.

当我选择/取消选择始终仅显示绿色背景时，无法更改单元格背景。

EDIT:

编辑：

// MARK: - TestAPIModel
struct TestAPIModel: Codable {
let page, perPage, total, totalPages: Int
var data: [Datum]
let support: Support

enum CodingKeys: String, CodingKey {
    case page
    case perPage = "per_page"
    case total
    case totalPages = "total_pages"
    case data, support
}
}

// MARK: - Datum
struct Datum: Codable {
let id: Int
let name: String
let year: Int
let color, pantoneValue: String
var isSelected: Bool = false
enum CodingKeys: String, CodingKey {
    case id, name, year, color
    case pantoneValue = "pantone_value"
    case isSelected = "is_selected"

}
}

after changing model like above o/p:

如上图所示，更换机型后：

decodingFailed(Alamofire.AFError.responseSerializationFailed(reason: Alamofire.AFError.ResponseSerializationFailureReason.decodingFailed(error: Swift.DecodingError.keyNotFound(CodingKeys(stringValue: "is_selected", intValue: nil), Swift.DecodingError.Context(codingPath: [CodingKeys(stringValue: "data", intValue: nil), _JSONKey(stringValue: "Index 0", intValue: 0)], debugDescription: "No value associated with key CodingKeys(stringValue: "is_selected", intValue: nil) ("is_selected").", underlyingError: nil)))))

this is my serviceCAll case here how to check nil data please guide

这是我的服务Call Case在这里如何检查空数据请指导

var jsonData: TestAPIModel? {
didSet{
print(jsonData?.data)
}

Var jsonData：测试APIModel？{didSet{print(jsonData？.data)}

}

NetworkService.request("https://reqres.in/api/unknown", method: .get, parameters: parameters) { (result: Result<TestAPIModel, APIError>) in
        switch result {
        case .success(let user):
            print("response \(user)")
            self.jsonData = user
            self.collectionView.reloadData()

        case .failure(let error):
            print("Error: \(error)")
        }
    }

An extra array for the selected state is very bad practice. It's cumbersome to maintain and you have to set the color accordingly in cellForItemAt because cells are reused when the user scrolls.

为所选状态添加额外的数组是非常糟糕的做法。它维护起来很麻烦，而且您必须在cell ForItemAt中相应地设置颜色，因为当用户滚动时，单元格会被重用。

A better way is a struct for the data source with a member isSelected

一种更好的方法是为数据源创建一个结构，其中成员为isSelected

struct Person {
    let name: String
    var isSelected = false
}

Then the data source array is

则数据源数组为

var people = [Person]()

and the data source and methods are

数据源和方法为

func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    people.count
}

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "TestCollectionCell", for: indexPath) as! TestCollectionCell
    cell.layoutIfNeeded()
    let person = people[indexPath.row]
    cell.titleLbl.text = person.name
    cell.backgroundColor = person.isSelected ? .red : .yellow
    return cell
}

In didSelect just toggle isSelected of the item at given indexPath and reload the item

在didSelect中，只需在给定的indexPath处切换项的isSelected并重新加载项

func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath)     {

    print("in select..")

    people[indexPath.row].isSelected.toggle()
    collectionView.reloadItems(at: [indexPath])
}

Try

尝试

let cell = collectionView.cellForItem(at: indexPath) as! TestCollectionCell
cell.contentView.backgroundColor = UIColor.white (What ever color u want change)