[SwiftUI] 階層的プルダウンメニューを作る方法 (menu と Picker の比較から)

//
//  ContentView.swift
//
//  Created by : Tomoaki Yagishita on 2021/05/17
//  © 2021  SmallDeskSoftware
//

import SwiftUI

struct ContentView: View {
    let data = [0,1,2,3,4]
    @State var selection0:Int = 0
    var body: some View {
        VStack {
            HStack {
                Picker(selection: $selection0, label: Text("Picker"), content: {
                    ForEach(data, id:\.self) { value in
                        Text("\(value)")
                            .tag(value)
                    }
                })
            }
        }
        .padding(50)
    }
}

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

//
//  ContentView.swift
//
//  Created by : Tomoaki Yagishita on 2021/05/17
//  © 2021  SmallDeskSoftware
//

import SwiftUI

struct ContentView: View {
    let data = [0,1,2,3,4]
    let option = [[0,1],[2,3,4],[5,6],[7,8,9], [10,11,12,13,14,15]]
    @State var selection0:Int = -1
    @State var selection1:Int = 0
    @State var optionVisible = false
    var body: some View {
        VStack {
            HStack {
                Picker(selection: $selection0, label: Text("Picker"), content: {
                    ForEach(data, id:\.self) { value in
                        Text("\(value)")
                            .tag(value)
                    }
                })
                if optionVisible {
                    // (1)
                    Picker(selection: $selection1, label: Text("Option"), content: {
                        ForEach(option[selection0], id:\.self) { value in
                            Text("\(value)")
                                .tag(value)
                        }
                    })
                }
            }
            .onChange(of: selection0, perform: { value in
                // (2)
                if selection0 != 3 {
                    optionVisible = true
                    selection1 = option[selection0][0]
                } else {
                    optionVisible = false
                }
            })
        }
        .onAppear {
            selection0 = 0
        }
        .padding(49)
    }
}

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

//
//  ContentView.swift
//
//  Created by : Tomoaki Yagishita on 2021/05/17
//  © 2021  SmallDeskSoftware
//

import SwiftUI

struct ContentView: View {
    var body: some View {
        VStack {
            Menu {
                Button(action: {
                  // do something
                }, label: {
                    Text("Item1")
                })
                Button(action: {
                  // do something
                }, label: {
                    Text("Item2")
                })
            } label: {
                Text("Menu")
            }
        .padding(49)
    }
}

//
//  ContentView.swift
//
//  Created by : Tomoaki Yagishita on 2021/05/17
//  © 2021  SmallDeskSoftware
//

import SwiftUI

struct ContentView: View {
    @State var menuTitle:String = "Menu"
    @State var menuToggle = false
    var body: some View {
        VStack {
            if menuToggle {
                menu()
            } else {
                menu()
            }
            
        }
        .padding(49)
    }
    
    func menu() -> some View {
        Menu(menuTitle) {
            Button(action: {
                menuTitle = "Item1"
                menuToggle.toggle()
            }, label: {
                Text("Item1")
            })
            Menu("Optional"){
                Button(action: {
                    menuTitle = "Opt1"
                    menuToggle.toggle()
                }, label: {
                    Text("Opt1")
                })
                Button(action: {
                    menuTitle = "Opt2"
                    menuToggle.toggle()
                }, label: {
                    Text("Opt2")
                })
            }
            Button(action: {
                menuTitle = "Item2"
                menuToggle.toggle()
            }, label: {
                Text("Item2")
            })
        }
    }
    
}

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