[移动开发]Mac OS Swift UI 三栏布局

import SwiftUI

var leftItems = ["left1", "left2", "left3", "left4"]
var middleItems1 = ["middle1-1", "middle1-2"]
var middleItems2 = ["middle2-1", "middle2-2", "middle3-3"]
var middleItems3 = ["middle4-1", "middle4-2", "middle4-3", "middle4-4"]
struct ContentView: View {
    @State var select: String? = "left1"
    
    var body: some View
    {
        VStack
        {
            NavigationView
            {
                List
                {
                    ForEach((0..<leftItems.count), id: \.self)
                    {index in
                        NavigationLink(destination: MiddleView(page: index), tag: leftItems[index], selection: $select)
                        {
                            Text(leftItems[index])
                                .frame(height: 20)
                        }
                    }
                    Spacer()

                }
                                .listStyle(SidebarListStyle())
            }

            .toolbar
            {
                Text("title")
                Button(action: {})
                {
                    Label("test", systemImage: "square.and.arrow.down")
                }
            }
            .navigationTitle(select!)
//            .navigationSubtitle("\(leftItems.count) items")
            .navigationViewStyle(DoubleColumnNavigationViewStyle())
        }
    }
}

struct MiddleView: View {
    
    public var page: Int
    
    var body: some View {
        NavigationView {
            
            if page == 0 {
                List {
                    ForEach((0..<middleItems1.count), id: \.self)
                    {index in
                        NavigationLink(destination: Text(middleItems1[index]))
                        {
                            Text(middleItems1[index])
                                .frame(height: 20)
                        }
                    }
                }
            }else if page == 1 {
                List {
                    ForEach((0..<middleItems2.count), id: \.self)
                    {index in
                        NavigationLink(destination: Text(middleItems2[index]))
                        {
                            Text(middleItems2[index])
                                .frame(height: 40)
                        }
                    }
                }
            }else {
                List {
                    ForEach((0..<middleItems3.count), id: \.self)
                    {index in
                        NavigationLink(destination: Text(middleItems3[index]))
                        {
                            Text(middleItems3[index])
                                .frame(height: 50)
                        }
                    }
                }
            }
        }
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

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