SwiftUI | 使用 onDrag 和 onDrop 对单个 LazyGrid 中的项目重新排序？

Question

我想知道是否可以使用View.onDrag和手动View.onDrop添加拖放重新排序LazyGrid？

虽然我能够使用 使每个项目都可以拖动onDrag，但我不知道如何实现放置部分。

这是我正在试验的代码：

import SwiftUI

//MARK: - Data

struct Data: Identifiable {
    let id: Int
}

//MARK: - Model

class Model: ObservableObject {
    @Published var data: [Data]
    
    let columns = [
        GridItem(.fixed(160)),
        GridItem(.fixed(160))
    ]
    
    init() {
        data = Array<Data>(repeating: Data(id: 0), count: 100)
        for i in 0..<data.count {
            data[i] = Data(id: i)
        }
    }
}

//MARK: - Grid

struct ContentView: View {
    @StateObject private var model = Model()
    
    var body: some View {
        ScrollView {
            LazyVGrid(columns: model.columns, spacing: 32) {
                ForEach(model.data) { d in
                    ItemView(d: d)
                        .id(d.id)
                        .frame(width: 160, height: 240)
                        .background(Color.green)
                        .onDrag { return NSItemProvider(object: String(d.id) as NSString) }
                }
            }
        }
    }
}

//MARK: - GridItem

struct ItemView: View {
    var d: Data
    
    var body: some View {
        VStack {
            Text(String(d.id))
                .font(.headline)
                .foregroundColor(.white)
        }
    }
}

谢谢！

Answer 1

SwiftUI 2.0

这里完成了可能的方法的简单演示（没有对其进行太多调整，`因为演示代码增长很快）。

重点是：a) 重新排序不假设等待删除，因此应该即时跟踪；b) 为避免与坐标共舞，通过网格项视图处理放置更简单；c) 在数据模型中找到移动的位置并执行此操作，因此 SwiftUI 自己为视图设置动画。

使用 Xcode 12b3 / iOS 14 测试

import SwiftUI
import UniformTypeIdentifiers

struct GridData: Identifiable, Equatable {
    let id: Int
}

//MARK: - Model

class Model: ObservableObject {
    @Published var data: [GridData]

    let columns = [
        GridItem(.fixed(160)),
        GridItem(.fixed(160))
    ]

    init() {
        data = Array(repeating: GridData(id: 0), count: 100)
        for i in 0..<data.count {
            data[i] = GridData(id: i)
        }
    }
}

//MARK: - Grid

struct DemoDragRelocateView: View {
    @StateObject private var model = Model()

    @State private var dragging: GridData?

    var body: some View {
        ScrollView {
           LazyVGrid(columns: model.columns, spacing: 32) {
                ForEach(model.data) { d in
                    GridItemView(d: d)
                        .overlay(dragging?.id == d.id ? Color.white.opacity(0.8) : Color.clear)
                        .onDrag {
                            self.dragging = d
                            return NSItemProvider(object: String(d.id) as NSString)
                        }
                        .onDrop(of: [UTType.text], delegate: DragRelocateDelegate(item: d, listData: $model.data, current: $dragging))
                }
            }.animation(.default, value: model.data)
        }
    }
}

struct DragRelocateDelegate: DropDelegate {
    let item: GridData
    @Binding var listData: [GridData]
    @Binding var current: GridData?

    func dropEntered(info: DropInfo) {
        if item != current {
            let from = listData.firstIndex(of: current!)!
            let to = listData.firstIndex(of: item)!
            if listData[to].id != current!.id {
                listData.move(fromOffsets: IndexSet(integer: from),
                    toOffset: to > from ? to + 1 : to)
            }
        }
    }

    func dropUpdated(info: DropInfo) -> DropProposal? {
        return DropProposal(operation: .move)
    }

    func performDrop(info: DropInfo) -> Bool {
        self.current = nil
        return true
    }
}

//MARK: - GridItem

struct GridItemView: View {
    var d: GridData

    var body: some View {
        VStack {
            Text(String(d.id))
                .font(.headline)
                .foregroundColor(.white)
        }
        .frame(width: 160, height: 240)
        .background(Color.green)
    }
}

编辑

以下是如何修复拖放到任何网格项目之外时永不消失的拖动项目：

struct DropOutsideDelegate: DropDelegate { 
    @Binding var current: GridData?  
        
    func performDrop(info: DropInfo) -> Bool {
        current = nil
        return true
    }
}

struct DemoDragRelocateView: View {
    ...

    var body: some View {
        ScrollView {
            ...
        }
        .onDrop(of: [UTType.text], delegate: DropOutsideDelegate(current: $dragging))
    }
}

Answer 2

ForEach对于那些寻求通用方法来抽象视图的人来说，这是我的解决方案（基于 Asperi 的答案）：

struct ReorderableForEach<Content: View, Item: Identifiable & Equatable>: View {
    let items: [Item]
    let content: (Item) -> Content
    let moveAction: (IndexSet, Int) -> Void
    
    // A little hack that is needed in order to make view back opaque
    // if the drag and drop hasn't ever changed the position
    // Without this hack the item remains semi-transparent
    @State private var hasChangedLocation: Bool = false

    init(
        items: [Item],
        @ViewBuilder content: @escaping (Item) -> Content,
        moveAction: @escaping (IndexSet, Int) -> Void
    ) {
        self.items = items
        self.content = content
        self.moveAction = moveAction
    }
    
    @State private var draggingItem: Item?
    
    var body: some View {
        ForEach(items) { item in
            content(item)
                .overlay(draggingItem == item && hasChangedLocation ? Color.white.opacity(0.8) : Color.clear)
                .onDrag {
                    draggingItem = item
                    return NSItemProvider(object: "\(item.id)" as NSString)
                }
                .onDrop(
                    of: [UTType.text],
                    delegate: DragRelocateDelegate(
                        item: item,
                        listData: items,
                        current: $draggingItem,
                        hasChangedLocation: $hasChangedLocation
                    ) { from, to in
                        withAnimation {
                            moveAction(from, to)
                        }
                    }
                )
        }
    }
}

尽管DragRelocateDelegate我让它更通用、更安全，但基本上保持不变：

struct DragRelocateDelegate<Item: Equatable>: DropDelegate {
    let item: Item
    var listData: [Item]
    @Binding var current: Item?
    @Binding var hasChangedLocation: Bool

    var moveAction: (IndexSet, Int) -> Void

    func dropEntered(info: DropInfo) {
        guard item != current, let current = current else { return }
        guard let from = listData.firstIndex(of: current), let to = listData.firstIndex(of: item) else { return }
        
        hasChangedLocation = true

        if listData[to] != current {
            moveAction(IndexSet(integer: from), to > from ? to + 1 : to)
        }
    }
    
    func dropUpdated(info: DropInfo) -> DropProposal? {
        DropProposal(operation: .move)
    }
    
    func performDrop(info: DropInfo) -> Bool {
        hasChangedLocation = false
        current = nil
        return true
    }
}

最后是实际用法：

ReorderableForEach(items: itemsArr) { item in
    SomeFancyView(for: item)
} moveAction: { from, to in
    itemsArr.move(fromOffsets: from, toOffset: to)
}

Answer 3

上面的优秀解决方案还提出了一些额外的问题，所以以下是我在 1 月 1 日宿醉后想出的解决方案（抱歉，我的表达不够雄辩）：

1. 如果您选择一个网格项并释放它（以取消），则视图不会重置

我添加了一个布尔值来检查视图是否已被拖动，如果还没有，那么它首先不会隐藏视图。这有点像黑客，因为它并没有真正重置，它只是推迟隐藏视图，直到它知道您想要拖动它。即，如果您拖动得非常快，您可以在视图隐藏之前短暂地看到它。

2. 如果将网格项放在视图之外，则视图不会重置

这个问题已经通过添加 dropOutside 委托得到了部分解决，但 SwiftUI 不会触发它，除非您有背景视图（如颜色），我认为这引起了一些混乱。因此，我添加了灰色背景来说明如何正确触发它。

希望这对任何人都有帮助：

import SwiftUI
import UniformTypeIdentifiers

struct GridData: Identifiable, Equatable {
    let id: String
}

//MARK: - Model

class Model: ObservableObject {
    @Published var data: [GridData]

    let columns = [
        GridItem(.flexible(minimum: 60, maximum: 60))
    ]

    init() {
        data = Array(repeating: GridData(id: "0"), count: 50)
        for i in 0..<data.count {
            data[i] = GridData(id: String("\(i)"))
        }
    }
}

//MARK: - Grid

struct DemoDragRelocateView: View {
    @StateObject private var model = Model()

    @State private var dragging: GridData? // I can't reset this when user drops view ins ame location as drag started
    @State private var changedView: Bool = false

    var body: some View {
        VStack {
            ScrollView(.vertical) {
               LazyVGrid(columns: model.columns, spacing: 5) {
                    ForEach(model.data) { d in
                        GridItemView(d: d)
                            .opacity(dragging?.id == d.id && changedView ? 0 : 1)
                            .onDrag {
                                self.dragging = d
                                changedView = false
                                return NSItemProvider(object: String(d.id) as NSString)
                            }
                            .onDrop(of: [UTType.text], delegate: DragRelocateDelegate(item: d, listData: $model.data, current: $dragging, changedView: $changedView))
                            
                    }
                }.animation(.default, value: model.data)
            }
        }
        .frame(maxWidth:.infinity, maxHeight: .infinity)
        .background(Color.gray.edgesIgnoringSafeArea(.all))
        .onDrop(of: [UTType.text], delegate: DropOutsideDelegate(current: $dragging, changedView: $changedView))
    }
}

struct DragRelocateDelegate: DropDelegate {
    let item: GridData
    @Binding var listData: [GridData]
    @Binding var current: GridData?
    @Binding var changedView: Bool
    
    func dropEntered(info: DropInfo) {
        
        if current == nil { current = item }
        
        changedView = true
        
        if item != current {
            let from = listData.firstIndex(of: current!)!
            let to = listData.firstIndex(of: item)!
            if listData[to].id != current!.id {
                listData.move(fromOffsets: IndexSet(integer: from),
                    toOffset: to > from ? to + 1 : to)
            }
        }
    }

    func dropUpdated(info: DropInfo) -> DropProposal? {
        return DropProposal(operation: .move)
    }

    func performDrop(info: DropInfo) -> Bool {
        changedView = false
        self.current = nil
        return true
    }
    
}

struct DropOutsideDelegate: DropDelegate {
    @Binding var current: GridData?
    @Binding var changedView: Bool
        
    func dropEntered(info: DropInfo) {
        changedView = true
    }
    func performDrop(info: DropInfo) -> Bool {
        changedView = false
        current = nil
        return true
    }
}

//MARK: - GridItem

struct GridItemView: View {
    var d: GridData

    var body: some View {
        VStack {
            Text(String(d.id))
                .font(.headline)
                .foregroundColor(.white)
        }
        .frame(width: 60, height: 60)
        .background(Circle().fill(Color.green))
    }
}

Answer 4

我采用了一种在 macOS 上运行良好的不同方法。而不是使用.onDrag和.onDrop我使用.gesture(DragGesture)辅助类和修饰符。

以下是辅助对象（只需将其复制到新文件中）：

// Helper class for dragging objects inside LazyVGrid.
// Grid items must be of the same size
final class DraggingManager<Entry: Identifiable>: ObservableObject {
    
    let coordinateSpaceID = UUID()
    
    private var gridDimensions: CGRect = .zero
    private var numberOfColumns = 0
    private var numberOfRows = 0
    private var framesOfEntries = [Int: CGRect]() // Positions of entries views in coordinate space
    
    func setFrameOfEntry(at entryIndex: Int, frame: CGRect) {
        guard draggedEntry == nil else { return }
        framesOfEntries[entryIndex] = frame
    }
    
    var initialEntries: [Entry] = [] {
        didSet {
            entries = initialEntries
            calculateGridDimensions()
        }
    }
    @Published // Currently displayed (while dragging)
    var entries: [Entry]?
    
    var draggedEntry: Entry? { // Detected when dragging starts
        didSet { draggedEntryInitialIndex = initialEntries.firstIndex(where: { $0.id == draggedEntry?.id }) }
    }
    var draggedEntryInitialIndex: Int?
    
    var draggedToIndex: Int? { // Last index where device was dragged to
        didSet {
            guard let draggedToIndex, let draggedEntryInitialIndex, let draggedEntry else { return }
            var newArray = initialEntries
            newArray.remove(at: draggedEntryInitialIndex)
            newArray.insert(draggedEntry, at: draggedToIndex)
            withAnimation {
                entries = newArray
            }
        }
    }

    func indexForPoint(_ point: CGPoint) -> Int {
        let x = max(0, min(Int((point.x - gridDimensions.origin.x) / gridDimensions.size.width), numberOfColumns - 1))
        let y = max(0, min(Int((point.y - gridDimensions.origin.y) / gridDimensions.size.height), numberOfRows - 1))
        return max(0, min(y * numberOfColumns + x, initialEntries.count - 1))
    }

    private func calculateGridDimensions() {
        let allFrames = framesOfEntries.values
        let rows = Dictionary(grouping: allFrames) { frame in
            frame.origin.y
        }
        numberOfRows = rows.count
        numberOfColumns = rows.values.map(\.count).max() ?? 0
        let minX = allFrames.map(\.minX).min() ?? 0
        let maxX = allFrames.map(\.maxX).max() ?? 0
        let minY = allFrames.map(\.minY).min() ?? 0
        let maxY = allFrames.map(\.maxY).max() ?? 0
        let width = (maxX - minX) / CGFloat(numberOfColumns)
        let height = (maxY - minY) / CGFloat(numberOfRows)
        let origin = CGPoint(x: minX, y: minY)
        let size = CGSize(width: width, height: height)
        gridDimensions = CGRect(origin: origin, size: size)
    }
        
}

struct Draggable<Entry: Identifiable>: ViewModifier {
    
    @Binding
    var originalEntries: [Entry]
    let draggingManager: DraggingManager<Entry>
    let entry: Entry

    @ViewBuilder
    func body(content: Content) -> some View {
        if let entryIndex = originalEntries.firstIndex(where: { $0.id == entry.id }) {
            let isBeingDragged = entryIndex == draggingManager.draggedEntryInitialIndex
            let scale: CGFloat = isBeingDragged ? 1.1 : 1.0
            content.background(
                GeometryReader { geometry -> Color in
                    draggingManager.setFrameOfEntry(at: entryIndex, frame: geometry.frame(in: .named(draggingManager.coordinateSpaceID)))
                    return .clear
                }
            )
            .scaleEffect(x: scale, y: scale)
            .gesture(
                dragGesture(
                    draggingManager: draggingManager,
                    entry: entry,
                    originalEntries: $originalEntries
                )
            )
        }
        else {
            content
        }
    }
    
    func dragGesture<Entry: Identifiable>(draggingManager: DraggingManager<Entry>, entry: Entry, originalEntries: Binding<[Entry]>) -> some Gesture {
        DragGesture(coordinateSpace: .named(draggingManager.coordinateSpaceID))
            .onChanged { value in
                // Detect start of dragging
                if draggingManager.draggedEntry?.id != entry.id {
                    withAnimation {
                        draggingManager.initialEntries = originalEntries.wrappedValue
                        draggingManager.draggedEntry = entry
                    }
                }
                
                let point = draggingManager.indexForPoint(value.location)
                if point != draggingManager.draggedToIndex {
                    draggingManager.draggedToIndex = point
                }
            }
            .onEnded { value in
                withAnimation {
                    originalEntries.wrappedValue = draggingManager.entries!
                    draggingManager.entries = nil
                    draggingManager.draggedEntry = nil
                    draggingManager.draggedToIndex = nil
                }
            }
    }

}

extension View {
    // Allows item in LazyVGrid to be dragged between other items.
    func draggable<Entry: Identifiable>(draggingManager: DraggingManager<Entry>, entry: Entry, originalEntries: Binding<[Entry]>) -> some View {
        self.modifier(Draggable(originalEntries: originalEntries, draggingManager: draggingManager, entry: entry))
    }
}

现在要在视图中使用它，您必须做几件事：

• 创建一个draggingManager，它是StateObject

• 创建一个 var，它公开您正在使用的真实数组或在拖动过程中由draggingManager 使用的临时数组。

• 从draggingManager应用coordinateSpace到容器（LazyVGrid），这样draggingManager在处理过程中仅修改其数组的副本，并且可以在拖动完成后更新原始数组。

  结构 VirtualMachineSettingsDevicesView: 查看 {

    @ObservedObject
    var vmEntity: VMEntity
  
    @StateObject
    private var devicesDraggingManager = DraggingManager<VMDeviceInfo>()
    // Currently displaying devices - different during dragging.
    private var displayedDevices: [VMDeviceInfo] { devicesDraggingManager.entries ?? vmEntity.config.devices }
  
    var body: some View {
        Section("Devices") {
            LazyVGrid(columns: [.init(.adaptive(minimum: 64, maximum: 64))], alignment: .leading, spacing: 20) {
                Group {
                    ForEach(displayedDevices) { device in
                        Button(action: { configureDevice = device }) {
                            device.label
                                .draggable(
                                    draggingManager: devicesDraggingManager,
                                    entry: device,
                                    originalEntries: $vmEntity.config.devices
                                )
                        }
                    }
                    Button(action: { configureNewDevice = true }, label: { Label("Add device", systemImage: "plus") })
                }
                .labelStyle(IconLabelStyle())
            }
            .coordinateSpace(name: devicesDraggingManager.coordinateSpaceID)
            .frame(maxWidth: .infinity, maxHeight: .infinity)
            .buttonStyle(.plain)
        }
  

  }

Answer 5

以下是实现 on drop 部分的方法。但请记住，ondrop如果数据符合UTType. 有关UTType 的更多信息。

将 onDrop 实例添加到您的lazyVGrid。

           LazyVGrid(columns: model.columns, spacing: 32) {
                ForEach(model.data) { d in
                    ItemView(d: d)
                        .id(d.id)
                        .frame(width: 160, height: 240)
                        .background(Color.green)
                        .onDrag { return NSItemProvider(object: String(d.id) as NSString) }
                }
            }.onDrop(of: ["public.plain-text"], delegate: CardsDropDelegate(listData: $model.data))

创建一个 DropDelegate 来处理放置的内容和给定视图的放置位置。

struct CardsDropDelegate: DropDelegate {
    @Binding var listData: [MyData]

    func performDrop(info: DropInfo) -> Bool {
        // check if data conforms to UTType
        guard info.hasItemsConforming(to: ["public.plain-text"]) else {
            return false
        }
        let items = info.itemProviders(for: ["public.plain-text"])
        for item in items {
            _ = item.loadObject(ofClass: String.self) { data, _ in
                // idea is to reindex data with dropped view
                let index = Int(data!)
                DispatchQueue.main.async {
                        // id of dropped view
                        print("View Id dropped \(index)")
                }
            }
        }
        return true
    }
}

另外，唯一真正有用的参数performDrop是info.location放置位置的 CGPoint，将 CGPoint 映射到要替换的视图似乎不合理。我认为这OnMove将是一个更好的选择，并且将使您的数据/视图的移动变得轻而易举。我未能成功OnMove地在LazyVGrid.

由于LazyVGrid仍处于测试阶段并且必然会发生变化。我会避免使用更复杂的任务。

Answer 6

目标：对 HStack 中的项目重新排序

我试图找出在拖动图标以重新排序一组水平项目时如何在 macOS 的 SwiftUI 中利用此解决方案。感谢@ramzesenok 和@Asperi 提供的整体解决方案。我添加了 CGPoint 属性及其解决方案以实现所需的行为。请参阅下面的动画。

定义点

 @State private var drugItemLocation: CGPoint?

我在dropEntered、dropExited和performDropDropDelegate 函数中使用过。

func dropEntered(info: DropInfo) {
    if current == nil {
        current = item
        drugItemLocation = info.location
    }

    guard item != current, 
          let current = current,
          let from = icons.firstIndex(of: current),
          let toIndex = icons.firstIndex(of: item) else { return }

          hasChangedLocation = true
          drugItemLocation = info.location

    if icons[toIndex] != current {
        icons.move(fromOffsets: IndexSet(integer: from), toOffset: toIndex > from ? toIndex + 1 : toIndex)
    }
}

func dropExited(info: DropInfo) {
    drugItemLocation = nil
}

func performDrop(info: DropInfo) -> Bool {
   hasChangedLocation = false
   drugItemLocation = nil
   current = nil
   return true
}

对于完整的演示，我使用 Playgrounds创建了一个要点