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？

How to Update Array Index After Drag and Drop is Called in UserDefaults in CollectionView?

ios

swift

uicollectionview

delegates

nsuserdefaults