Swift - 检索数据后显示 UICollectionView

Question

我有一个collectionView，我通过从我的 Firestore 数据库中检索数据来填充它。我的问题是我想检索数据，并且只有在完成 collectionView 之后才会出现在 willDisplay 内部处理的动画。

这就是我检索数据的方式：

func getWishlists() {
    let db = Firestore.firestore()
    let userID = Auth.auth().currentUser!.uid
    db.collection("users").document(userID).collection("wishlists").order(by: "listIDX").getDocuments() { ( querySnapshot, error) in
        if let error = error {
            print(error.localizedDescription)
        }else {
            // get all documents from "wishlists"-collection and save attributes
            for document in querySnapshot!.documents {
                let documentData = document.data()
                let listName = documentData["name"]
                let listImageIDX = documentData["imageIDX"]

                // if-case for Main Wishlist
                if listImageIDX as? Int == nil {
                    self.dataSourceArray.append(Wishlist(name: listName as! String, image: UIImage(named: "iconRoundedImage")!, wishData: [Wish](), color: self.mainColor))
                    // set the drop down menu's options
                    self.dropDownButton.dropView.dropDownOptions.append(listName as! String)
                    self.dropDownButton.dropView.dropDownListImages.append(UIImage(named: "iconRoundedImage")!)
                }else {

                    self.dataSourceArray.append(Wishlist(name: listName as! String, image: self.images[listImageIDX as! Int], wishData: [Wish](), color: self.customColors[listImageIDX as! Int]))

                    self.dropDownButton.dropView.dropDownOptions.append(listName as! String)
                    self.dropDownButton.dropView.dropDownListImages.append(self.images[listImageIDX as! Int])
                }

                // reload collectionView and tableView
                self.theCollectionView.reloadData()
                self.dropDownButton.dropView.tableView.reloadData()

            }
        }
        self.getWishes()
    }
}

我在viewDidLoad 内部调用getWishlists，这就是我处理collectionView 的方式：

func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    // return 1 more than our data array (the extra one will be the "add item" cell)
    return dataSourceArray.count + 1
}

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {

    // if indexPath.item is less than data count, return a "Content" cell
    if indexPath.item < dataSourceArray.count {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "ContentCell", for: indexPath) as! ContentCell
        // set cell label
        cell.cellLabel.text = dataSourceArray[indexPath.item].name
        // set cell image
        cell.wishlistImage.image = dataSourceArray[indexPath.item].image          
        // set background color
        cell.imageView.backgroundColor = dataSourceArray[indexPath.item].color
        cell.wishCounterView.backgroundColor = dataSourceArray[indexPath.item].color
        cell.priceView.backgroundColor = dataSourceArray[indexPath.item].color



        cell.customWishlistTapCallback = {

            let heroID = "wishlistImageIDX\(indexPath)"
            cell.theView.heroID = heroID

            let addButtonHeroID = "addWishButtonID"
            self.addButton.heroID = addButtonHeroID     

            let vc = self.storyboard?.instantiateViewController(withIdentifier: "WishlistVC") as! WishlistViewController            

            vc.theTableView.tableView.reloadData()
            self.present(vc, animated: true, completion: nil)

        }

        return cell
    }

    // past the end of the data count, so return an "Add Item" cell
    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "AddItemCell", for: indexPath) as! AddItemCell

    // set the closure
    cell.tapCallback = {

        self.listNameTextfield.becomeFirstResponder()

        // let newListView appear
        UIView.animate(withDuration: 0.3, delay: 0, options: .curveEaseOut, animations: {
            self.blurrImage.alpha = 0.96
            self.blurrImage.transform = CGAffineTransform(translationX: 0, y: 0)
            self.newListView.transform = CGAffineTransform(translationX: 0, y: 0)
            self.view.layoutIfNeeded()
        })

        self.appWillEnterForegroundHandler()

    }

    return cell

}

// animate displaying cells
func collectionView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
    // Add animations here
    cell.alpha = 0

    UIView.animate(
        withDuration: 0.5,
        delay: 0.05 * Double(indexPath.row),
        animations: {
            cell.alpha = 1
    }) 
}

目前，单元格没有被动画化，而是在检索数据时稍等片刻后才显示出来。

Answer 1

willDisplay 是 pul 动画的正确位置；但是，它仅在您设置委托时才会触发。看起来您查看了数据源，否则您什么也看不到。设置委托和断点 willDisplay 以验证其被调用。