タブバーを作成する
Building our tab bar

//
//  MeView.swift
//  HotProspects
//

import SwiftUI

struct MeView: View {
    var body: some View {
        Text(/*@START_MENU_TOKEN@*/"Hello, World!"/*@END_MENU_TOKEN@*/)
    }
}

//
//  ProspectsView.swift
//  HotProspects

import SwiftUI

struct ProspectsView: View {
    enum FilterType {
        case none, contacted, uncontacted
    }
    
    let filter: FilterType
    
    var title: String {
        switch filter {
        case .none:
            return "Everyone"
        case .contacted:
            return "Contacted people"
        case .uncontacted:
            return "Uncontacted people"
        }
    }
    
    var body: some View {
        NavigationView {
            Text("Hello, World!")
                .navigationBarTitle(title)
        }
    }
}

//
//  ContentView.swift
//  HotProspects
//
//  Created by Naoki Abe on 2020/08/29.
//  Copyright © 2020 Naoki Abe. All rights reserved.
//

import SwiftUI

struct ContentView: View {
    var body: some View {
        TabView {
            ProspectsView(filter: .none)
                .tabItem {
                    Image(systemName: "person.3")
                    Text("Everyone")
                }
            ProspectsView(filter: .contacted)
                .tabItem {
                    Image(systemName: "checkmark.circle")
                    Text("Contacted")
                }
            ProspectsView(filter: .uncontacted)
                .tabItem {
                    Image(systemName: "questionmark.diamond")
                    Text("Uncontacted")
                }
            MeView()
                .tabItem {
                    Image(systemName: "person.crop.square")
                    Text("Me")
                }
        }
    }
}

@EnvironmentObjectを使用してタブ間でデータを共有する
Sharing data across tabs using @EnvironmentObject

複数のビュー間でそれを共有することになると、SwiftUIの環境の最も優れている点の1つはObservableObject、@ObservedObjectプロパティラッパーで使用していたのと同じプロトコルを使用することです。これは、@Publishedプロパティラッパーを使用してアナウンスする必要のあるプロパティをマークできることを意味します。
プロパティをSwiftUI環境にポストして、すべての子ビューがアクセスできるようにする必要があります。タブは内部にあるタブビューの子と見なされるため、タブを環境に追加すると、TabViewすべてのProspectsViewインスタンスがそのオブジェクトを取得します。

したがって、この修飾子をTabViewinに追加しContentViewます。

import SwiftUI

class Prospect: Identifiable, Codable {
    let id = UUID()
    var name = "Anonymous"
    var emailAddress = ""
    var isContacted = false
}

class Prospects: ObservableObject {
    @Published var people: [Prospect]

    init() {
        self.people = []
    }
}

//
//  ProspectsView.swift
//  HotProspects

import SwiftUI

struct ProspectsView: View {
    @EnvironmentObject var prospects: Prospects
    
    enum FilterType {
        case none, contacted, uncontacted
    }
    
    let filter: FilterType
    
    var title: String {
        switch filter {
        case .none:
            return "Everyone"
        case .contacted:
            return "Contacted people"
        case .uncontacted:
            return "Uncontacted people"
        }
    }
    
    var body: some View {
        NavigationView {
            Text("People: \(prospects.people.count)")
                .navigationBarTitle(title)
                .navigationBarItems(trailing: Button(action: {
                    let prospect = Prospect()
                    prospect.name = "Paul Hudson"
                    prospect.emailAddress = "paul@hackingwithswift.com"
                    self.prospects.people.append(prospect)
                }) {
                    Image(systemName: "qrcode.viewfinder")
                    Text("Scan")
                })
        }
    }
}

import SwiftUI

struct ContentView: View {
    var prospects = Prospects()
    
    var body: some View {
        TabView {
            ProspectsView(filter: .none)
                .tabItem {
                    Image(systemName: "person.3")
                    Text("Everyone")
                }
            ProspectsView(filter: .contacted)
                .tabItem {
                    Image(systemName: "checkmark.circle")
                    Text("Contacted")
                }
            ProspectsView(filter: .uncontacted)
                .tabItem {
                    Image(systemName: "questionmark.diamond")
                    Text("Uncontacted")
                }
            MeView()
                .tabItem {
                    Image(systemName: "person.crop.square")
                    Text("Me")
                }
        }
        .environmentObject(prospects)
    }
}

SwiftUIリストの動的フィルタリング
Dynamically filtering a SwiftUI List

//
//  ProspectsView.swift
//  HotProspects
//
//  Created by Naoki Abe on 2020/09/01.
//  Copyright © 2020 Naoki Abe. All rights reserved.
//

import SwiftUI

struct ProspectsView: View {
    @EnvironmentObject var prospects: Prospects
    
    enum FilterType {
        case none, contacted, uncontacted
    }
    
    let filter: FilterType
    
    var title: String {
        switch filter {
        case .none:
            return "Everyone"
        case .contacted:
            return "Contacted people"
        case .uncontacted:
            return "Uncontacted people"
        }
    }
    
    var filteredProspects: [Prospect] {
        switch filter {
        case .none:
            return prospects.people
        case .contacted:
            return prospects.people.filter { $0.isContacted }
        case .uncontacted:
            return prospects.people.filter { !$0.isContacted }
        }
    }
    
    var body: some View {
        NavigationView {
                // Text("People: \(prospects.people.count)")
                List {
                    ForEach(filteredProspects) { prospect in
                        VStack(alignment: .leading) {
                            Text(prospect.name)
                                .font(.headline)
                            Text(prospect.emailAddress)
                                .foregroundColor(.secondary)
                        }
                    }
                }
                .navigationBarTitle(title)
                .navigationBarItems(trailing: Button(action: {
                    let prospect = Prospect()
                    prospect.name = "Paul Hudson"
                    prospect.emailAddress = "paul@hackingwithswift.com"
                    self.prospects.people.append(prospect)
                }) {
                    Image(systemName: "qrcode.viewfinder")
                    Text("Scan")
                })
        }
    }
}