快速用户界面 |使用 onDrag 和 onDrop 在一个 LazyGrid 中重新排序项目？

Question

我想知道是否可以使用 View.onDrag 和 View.onDrop 在一个 LazyGrid 中手动添加拖放重新排序？

虽然我能够使用 onDrag 使每个项目都可拖动，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

以下是实现放置部分的方法。但请记住，如果数据符合 UTType，ondrop 可以允许从应用程序外部放入内容。更多关于 UTTypes.

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 以使用给定视图处理放置的内容和放置位置。

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performDrop唯一真正有用的参数是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 OnMove 会是一个更好的选择，它会让移动 data/Views 变得轻而易举。我没有成功让 OnMove 在 LazyVGrid 中工作。

因为 LazyVGrid 仍处于测试阶段，并且肯定会发生变化。我会放弃使用更复杂的任务。

Answer 2

SwiftUI 2.0

这是可能方法的完整简单演示（没有对其进行太多调整，`因为代码增长速度与演示一样快）。

要点是：a) 重新排序不需要等待丢弃，因此应该即时跟踪； b) 为了避免与坐标共舞，处理网格项目视图的下降更简单； c) 在数据模型中找到移动到哪里并执行此操作，因此 SwiftUI 会自行为视图设置动画。

测试 Xcode 12b3 / iOS 14

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

以下是如何修复拖动项在拖放到任何网格项之外时永不消失的问题：

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))
    }
}

backup

Answer 3

上面的优秀解决方案还提出了一些额外的问题，所以这是我在 1 月 1 日宿醉时可以想出的（即，为少于 eloquent 道歉）：

如果您选择一个 griditem 并释放它（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，如果没有，那么它不会首先隐藏视图。这有点 hack，因为它并没有真正重置，它只是推迟隐藏视图，直到它知道你想拖动它。 IE。如果您拖动得非常快，您可以在隐藏之前短暂地看到视图。

如果将 griditem 拖放到视图外，则不会重置视图

这个问题已经通过添加 dropOutside 委托得到了部分解决，但是 SwiftUI 不会触发它，除非你有背景视图（比如颜色），我认为这引起了一些混乱。因此，我添加了一个灰色背景来说明如何正确触发它。

希望这对任何人有帮助：

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

这是我的解决方案（基于 Asperi 的回答），适用于那些为 ForEach 寻求通用方法的人，我 将视图抽象化了 :

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)
                        }
                    }
                )
        }
    }
}

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

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 5

目标：重新排序 HStack 中的项目

我试图弄清楚在将图标拖动到 re-order 一组水平项目时如何在 SwiftUI for macOS 中利用此解决方案。感谢@ramzesenok 和@Asperi 的整体解决方案。我添加了一个 CGPoint 属性以及他们的解决方案以实现所需的行为。请看下面的动画。

定义点

 @State private var drugItemLocation: CGPoint?

我在 dropEntered、dropExited 和 performDrop DropDelegate 函数中使用。


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
}

为了完整演示，我使用 Playgrounds

创建了一个 gist

快速用户界面 |使用 onDrag 和 onDrop 在一个 LazyGrid 中重新排序项目？

SwiftUI | Using onDrag and onDrop to reorder Items within one single LazyGrid?

ios

swift

swiftui

collectionview

xcode12

编辑

最后是实际用法：

目标：重新排序 HStack 中的项目