CollectionView 的UserDefaults 中调用拖放后如何更新数组索引？

Question

我正在创建一个演示，其中我有拖放功能，拖放功能工作得很好，我担心的是，当我关闭应用程序并再次返回视图时，同样是索引显示在数组中，我想像在索引处拖放一样获取数组。

这是我的代码

CollectionView 方法

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

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "ImageCell", for: indexPath) as! ImageCell
    cell.lbl.text = array[indexPath.row]
    cell.img.layer.cornerRadius = cell.img.frame.size.width / 2
    cell.lbl.layer.cornerRadius = cell.lbl.frame.size.width / 2
    return cell
}

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {

    return CGSize(width: (collectionView.frame.size.width / 2) - 20, height: 200)
}

func collectionView(_ collectionView: UICollectionView, canMoveItemAt indexPath: IndexPath) -> Bool {
    return true
}

func collectionView(_ collectionView: UICollectionView, moveItemAt sourceIndexPath: IndexPath, to destinationIndexPath: IndexPath) {

    let item = array.remove(at: sourceIndexPath.item)
    defaults.removeObject(forKey: "data")
    array.insert(item, at: destinationIndexPath.item)
    defaults.set(item, forKey: "data")
    defaults.synchronize()
    
    print(item )
}

View 加载和 LongPressGesture 方法

@IBOutlet weak var collectionView: UICollectionView!
var array = ["Fateh", "Parul", "Jitendra", "Javed", "Brijesh","Pandey Ji"]
let defaults = UserDefaults.standard
var longPress : UILongPressGestureRecognizer!


override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view.
    if UserDefaults.standard.array(forKey: "data") == nil {
         // userDefault has a value
   
        defaults.set(array, forKey: "data")
        
    } else  {
        let newData = defaults.object(forKey: "data")
        array = newData as! [String]
    }
    
    
    collectionView.delegate = self
    collectionView.dataSource = self
    longPress = UILongPressGestureRecognizer(target: self, action: #selector(handleLongGesture(gesture:)))
    collectionView.addGestureRecognizer(longPress)
}

@objc func handleLongGesture(gesture : UILongPressGestureRecognizer){
    switch gesture.state {
    case .began:
        guard let selectedIndex = collectionView.indexPathForItem(at: gesture.location(in: collectionView)) else {
            break
        }
        collectionView.beginInteractiveMovementForItem(at: selectedIndex)
    case .changed:
        collectionView.updateInteractiveMovementTargetPosition(gesture.location(in: gesture.view))
        
    case .ended:
        collectionView.endInteractiveMovement()
        defaults.synchronize()
    @unknown default:
        collectionView.cancelInteractiveMovement()
    }
}

Answer 1

在 viewDidLoad 中，如果 UserDefaults 中没有已保存的数据，则您正在这样做：

defaults.set(array, forKey: "data")

您正在将数组设置为数据。

在 moveItemAt 中，您正在这样做：

defaults.set(item, forKey: "data")

您仅将单个 item 设置为数据，而您应该将更新后的 array 设置为数据。

作为旁注，不需要 defaults.synchronize() ...来自 Apple 的 docs:

synchronize()

Waits for any pending asynchronous updates to the defaults database and returns; this method is unnecessary and shouldn't be used.

CollectionView 的UserDefaults 中调用拖放后如何更新数组索引？

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