我想使用 API collectionView.insertItems(at:) 一个一个地加载 Collection View 的单元格。在线有许多答案通过动画化 willDisplayCell 和其他方法内部单元格的 alpha 来实现这一点，例如这里 - link .然而，没有什么是完美的。使用 collectionView.insertItems(at:) 的原因是动画已经内置，无需修改。

但是使用 collectionView.insertItems(at:)，我得到如下错误:

*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Invalid update: invalid number of items in section 0. The number of items contained in an existing section after the update (5) must be equal to the number of items contained in that section before the update (5), plus or minus the number of items inserted or deleted from that section (1 inserted, 0 deleted) and plus or minus the number of items moved into or out of that section (0 moved in, 0 moved out).

这是我所拥有的示例，如上所示它正在崩溃，但我认为这是一个正确方向的开始(希望如此):

class ViewController: UIViewController {

    @IBOutlet weak var collectionView: UICollectionView!

    /// This array is populated from a network call.
    let images = [Image]()

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)

        animateCells()
    }

    func animateCells() {
        let indexPaths = [IndexPath(item: 0, section: 0),
                          IndexPath(item: 1, section: 0),
                          IndexPath(item: 2, section: 0),
                          IndexPath(item: 3, section: 0),
                          IndexPath(item: 4, section: 0)]

        for indexPath in indexPaths {
            let delayTime = 0.1 + Double(indexPath.row) * 0.3

            delay(delayTime) {
                self.collectionView.performBatchUpdates({
                    self.collectionView.insertItems(at: [indexPath])
                }, completion: nil)
            }
        }
    }

    func delay(_ delay: TimeInterval, closure: @escaping () -> Void) {
        let when = DispatchTime.now() + delay
        DispatchQueue.main.asyncAfter(deadline: when, execute: closure)
    }
}

// MARK: - UICollectionViewDataSource

extension ViewController: UICollectionViewDataSource {
    func numberOfSections(in collectionView: UICollectionView) -> Int {
        return 1
    }

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

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cell", for: indexPath)

        return cell
    }
}

我看到的主要问题之一是我在 numberOfItemsInSection 中执行了 return images.count。

有什么想法吗？

最佳答案

我用你的代码做了一个演示，发现了你的错误

When you are inserting items in your collection view there are already 5 items in your collection view in that position so you can not insert new cells there because your images array has only 5 items which are already been displayed.

请找到下面的工作代码->

    class ViewController: UIViewController {

    @IBOutlet weak var collectionView: UICollectionView!

    //Array for collectionView
    var images :[UIImage] = []

    //This array will populate from network call
    var arrAllImagesFromNetwork : [UIImage] = Array(repeating: UIImage(named: "img1")!, count: 5)

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)

        animateCells()

    }

    func animateCells() {
        let indexPaths = [IndexPath(item: 0, section: 0),
                          IndexPath(item: 1, section: 0),
                          IndexPath(item: 2, section: 0),
                          IndexPath(item: 3, section: 0),
                          IndexPath(item: 4, section: 0)]



        for indexPath in indexPaths {
            let delayTime = 0.1 + Double(indexPath.row) * 0.3

            delay(delayTime) {

                self.images.append(self.arrAllImagesFromNetwork[indexPath.row])

                self.collectionView.performBatchUpdates({
                    self.collectionView.insertItems(at: [indexPath])
                }, completion: nil)
            }
        }
    }

    func delay(_ delay: TimeInterval, closure: @escaping () -> Void) {
        let when = DispatchTime.now() + delay
        DispatchQueue.main.asyncAfter(deadline: when, execute: closure)
    }
}

// MARK: - UICollectionViewDataSource

extension ViewController: UICollectionViewDataSource {
    func numberOfSections(in collectionView: UICollectionView) -> Int {
        return 1
    }

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

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cell", for: indexPath)

        return cell
    }
}

关于iOS - 称重传感器一个接一个，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/44448561/