收藏視圖不更新

Question

我在分段控制中有 4 個類別。 當我按下其中一個時，集合視圖應顯示特定類別的產品。 但是，集合視圖不是重用單元格並僅顯示新項目，而是顯示舊項目，最后添加帶有新項目的新單元格。

使用 reloadData() 的合適位置在哪里。 或者，也許我錯過了什么？

這是我的代碼

private lazy var segmentedControl: UISegmentedControl = {
    var control = UISegmentedControl(items: ["All", "Men", "Women", "Jewelery", "Electro"])
    control.selectedSegmentTintColor = .black
    control.setTitleTextAttributes([.foregroundColor: UIColor.white], for: .selected)
    control.tintColor = .white
   control.selectedSegmentIndex = 0
    control.addTarget(self, action: #selector(segmentChanged(_ :)), for: .valueChanged)
    return control
}()

override func viewDidLoad() {
    super.viewDidLoad()
  
    collectionView.delegate = self
    collectionView.dataSource = self
    
    networkManager.delegate = self
    
    setupMainStackView()
    setupCollectionView()
    networkManager.loadProducts(category: .all)
    performSearch() 
}

func performSearch() {
    if let category = NetworkManager.Category(rawValue: segmentedControl.selectedSegmentIndex) {
        networkManager.loadProducts(category: category)
    
        collectionView.reloadData()
    }
   // collectionView.reloadData()
}
@objc func segmentChanged(_ sender: UISegmentedControl) {
    performSearch()
}

// MARK: - 數據源擴展 MainViewController: UICollectionViewDataSource {

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

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
  let cell = collectionView.dequeueReusableCell(withReuseIdentifier: MainViewCollectionViewCell.identifier, for: indexPath) as! MainViewCollectionViewCell
  let listOfProduct = productResults[indexPath.row]
    cell.configure(for: listOfProduct)

        return cell
}

}

這就是我搜索類別的方式

enum Category: Int {
     case all = 0
     case menSClothing = 1
     case womenSClothing = 2
     case electronics = 3
     case jewelery = 4
    
    var type: String {
        switch self {
        case .all: return ""
        case .menSClothing: return "category/men's%20clothing"
        case .womenSClothing: return "category/women's%20clothing"
        case .electronics: return "category/electronics"
        case .jewelery: return "category/jewelery"
        }
    }
}
private func fakeStoreURL(category: Category) -> URL {
    let kind = category.type
    let url = URL(string: "https://fakestoreapi.com/products/" + "\(kind)")
    return url!
}

func loadProducts（類別：類別）{

    let url = fakeStoreURL(category: category)
    
    URLSession.shared.dataTask(with: url) {  data, response, error in
    if let error = error {
        print(error)
        return
    }
    guard let data = data else { return }
    do {
        var products = try JSONDecoder().decode([Product].self, from: data)
        products = self.parse(data: data)
        print(products)
        DispatchQueue.main.async {
            self.delegate?.didSendProductData(self, with: products)
        }
       
    } catch {
        print(error)
    }
}.resume()

}

Answer 1

問題就在這里

networkManager.loadProducts(category: category) 
collectionView.reloadData()

loadProducts是一個異步方法，並且集合的重新加載發生在網絡數據返回之前，因此您需要一個完成

func loadProducts(category: Category,completion:@escaping([Product]? -> ())) {
    
    let url = fakeStoreURL(category: category)
    
    URLSession.shared.dataTask(with: url) {  data, response, error in
    if let error = error {
        print(error)
        completion(nil)
        return
    }
    guard let data = data else { return }
    do {
        var products = try JSONDecoder().decode([Product].self, from: data)
        products = self.parse(data: data)
        print(products)
        DispatchQueue.main.async {
          completion(products)
        }
       
    } catch {
        print(error)
        completion(nil)
    }
}.resume()

}

然后

networkManager.loadProducts(category: category) { [weak self] products in
   guard let products = products else { return }
   self?.productResults = products
   self?.collectionView.reloadData()
 }