ios - 检索数据后不重新加载 Collection View

Question

情况:我正在从 Firebase 中提取数据。提取数据后，我想更新/重新加载我的 collectionView 表。

问题:collectionView 不更新。以下是带有一些解释的代码。

var allProducts = [Product]()

override func viewDidLoad() {
    super.viewDidLoad()

    mostPopularCollectionView.dataSource = self
    mostPopularCollectionView.delegate = self

    getAllProducts { (returnedProductArray) in
        self.allProducts = returnedProductArray
        self.mostPopularCollectionView.reloadData()
    }

}

1. 函数 getAllProducts 工作正常。如果我在闭包中打印 allProducts.count，我会得到正确的数字 (3)。
2. 如果我在闭包外打印 allProducts.count，我的计数为零。

3. 我尝试将 getAllProducts 函数放在 viewWillAppear 中，但它没有解决问题

   扩展 FeedTableViewController: UICollectionViewDataSource, UICollectionViewDelegate{

       func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
   
       return 3
   
   }
   
   func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
   
       guard let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "mostPopularCell", for: indexPath) as? MostPopularCollectionViewCell else {return UICollectionViewCell()}
   
   
       if allProducts.count > 0 {
           let product : Product = allProducts[indexPath.row]
           if let productImageUrl = product.imageUrlArray.first {
               cell.upadateCellUI(forProductName: product.title, forProductImage: productImageUrl, forProductPrice: product.price)
           }
           return cell
       } else {
           return cell
       }
   
   }
   
   func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
       let productVC = UIStoryboard.init(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "productVC") as! ProductViewController
       productVC.product = allProducts[indexPath.row]
       present(productVC, animated: true, completion: nil)
   }
   

好消息是，当我点击任何项目时，在下一个 viewController 出现时会选择正确的产品。

所以唯一的问题是如何让 collectionView 在从 Firebase 检索数据后重新加载？非常感谢任何帮助

这是用于从 Firebase 检索所有数据的 getAllProducts 函数。

//MARK:- Retrieve all products from Firebase
func getAllProducts (handler: @escaping (_ allProducts: [Product]) -> ()) {

    //TODO:- Create an empty array to store all product fetched from Firebase
    var productArray = [Product]()
    var imageUrlArray = [String]()

    //TODO:- Create reference to Firebase database
    let DB = Database.database().reference()

    //TODO:- Create reference to products
    let REF_PRODUCTS = DB.child("Product")

    //TODO:- Snapshot of all products in database
    REF_PRODUCTS.observeSingleEvent(of: .value) { (allProductsSnapshot) in
        guard let allProductsSnapshot = allProductsSnapshot.children.allObjects as? [DataSnapshot] else {return}

        for product in allProductsSnapshot {
            let title = product.childSnapshot(forPath: "name").value as! String
            let price = product.childSnapshot(forPath: "price").value as! String
            let id = product.childSnapshot(forPath: "id").value as! Int
            let viewCount = product.childSnapshot(forPath: "viewCount").value as! Int
            let description = product.childSnapshot(forPath: "description").value as! String

            let REF_IMAGEURL = REF_PRODUCTS.child(String(id)).child("image")

            REF_IMAGEURL.observeSingleEvent(of: .value, with: { (allImageUrlSnapshot) in
                guard let allImageUrlSnapshot = allImageUrlSnapshot.children.allObjects as? [DataSnapshot] else {return}

                for imageUrl in allImageUrlSnapshot {
                    let imageUrl = imageUrl.value as! String
                    imageUrlArray.append(imageUrl)
                }
            })

            let product = Product(title: title, price: price, imageUrlArray: imageUrlArray, description: description, viewCount: viewCount, id: id)
            productArray.append(product)
        }
        handler(productArray)
    }
}

Answer 1

您应该始终在主线程上更新您的 UI 元素。这里也不异常(exception)。只需在主线程上执行重新加载代码。

dispatch_async(dispatch_get_main_queue(), {
   self.mostPopularCollectionView.reloadData()
})

对于 Swift 3:

DispatchQueue.main.async { 
   self.mostPopularCollectionView.reloadData()
}