ios - SwiftUI |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 中添加拖放重新排序手动？
虽然我能够使用 onDrag 使每个项目都可拖动，我不知道如何实现丢弃部分。

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) 重新排序不假设等待丢弃，因此应动态跟踪； b)为了避免与坐标跳舞，处理网格项目 View 的拖放更简单； c) 在数据模型中找到要移动的内容并执行此操作，因此 SwiftUI 会自行为 View 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
以下是如何在拖放到任何网格项目之外时修复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))
    }
}

backup