UIViewRepresentableUICollectionView當視圖出現時如何滾動到某個點？

我有以下代碼，但我不確定將它放在我的 UIViewRepresntable 中的哪個位置。有什么建議么？

    let scrollTo = IndexPath(row: 25, section: 0)
    view.scrollToItem(at: scrollTo, at: .top, animated: false)


struct CollectionViewRepresentable: UIViewRepresentable {
    
    @StateObject var vm = CollectionViewModel()

    let view = UICollectionView(frame: .zero, collectionViewLayout: UICollectionViewCompositionalLayout.list(using: UICollectionLayoutListConfiguration(appearance: .plain)))
    
    func makeUIView(context: Context) -> UICollectionView {

        view.backgroundColor = UIColor.clear
        view.dataSource = context.coordinator
        view.delegate = context.coordinator
        view.register(ListCell.self, forCellWithReuseIdentifier: "listCell")
        return view
    }

    func updateUIView(_ uiView: UICollectionView, context: Context) {
    }

    func makeCoordinator() -> Coordinator {
        Coordinator(self)
    }

    class Coordinator: NSObject, UICollectionViewDelegate, UICollectionViewDataSource {
        private var parent: CollectionViewRepresentable

        init(_ collectionViewRepresentable: CollectionViewRepresentable) {
            self.parent = collectionViewRepresentable
        }

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

        func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
            let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "listCell", for: indexPath) as! ListCell
            let item = parent.vm.items[indexPath.row]
            cell.item = item
            return cell
        }
    }
}

當視圖出現時，我需要滾動到該位置。

uj5u.com熱心網友回復：

您可以使用ViewControllerRepresentable并利用視圖控制器可以覆寫viewWillAppear/viewDidAppear方法的事實，您可以在其中撰寫滾動代碼。

為此， subclass UICollectionViewController，并將所有與集合視圖相關的邏輯移到那里：

class MyCollectionViewController: UICollectionViewController {
    var vm = CollectionViewModel()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        collectionView.backgroundColor = UIColor.clear
        collectionView.register(ListCell.self, forCellWithReuseIdentifier: "listCell")
    }
    
    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        
        let scrollTo = IndexPath(row: 25, section: 0)
        collectionView.scrollToItem(at: scrollTo, at: .top, animated: false)
    }
    
    override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return vm.items.count
    }
    
    override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "listCell", for: indexPath) as! ListCell
        let item = vm.items[indexPath.row]
        cell.item = item
        return cell
    }
}

考慮到上述情況，SwiftUI 代碼簡化為如下所示：

struct CollectionViewRepresentable: UIViewControllerRepresentable {
    
    func makeUIViewController(context: Context) -> MyCollectionViewController {
        .init(collectionViewLayout: UICollectionViewFlowLayout())
    }
    
    func updateUIViewController(_ vc: MyCollectionViewController, context: Context) {
    }
}

uj5u.com熱心網友回復：

一個場景并不完全清楚，但可以使用外部State和Binding內部可表示，隨呼叫而變化updateUIView。

所以一個可能的解決方案是

@State private var scrollTo = IndexPath(row: 25, section: 0) // << in parent !! 

// ...

struct CollectionViewRepresentable: UIViewRepresentable {
    @Binding var scrollTo: IndexPath                       // << 1) !!
    @StateObject private var vm = CollectionViewModel()

    func makeUIView(context: Context) -> UICollectionView {
        let view = UICollectionView(...)    // << move creation here !!
        // ... other code
        return view
    }

    func updateUIView(_ uiView: UICollectionView, context: Context) {
       // called at start and when binding updated
       uiView.scrollToItem(at: scrollTo, at: .top, animated: false)  // << 2) !!
    }
// ... other code
}

標籤：迅速 迅捷 uicollectionview uiviewrepresentable

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