@EnvironmentObject

SceneDelegate.swift

//
//  SceneDelegate.swift
//
//  Created by Rostyslav Druzhchenko on 14.01.2020.
//  Copyright © 2020 Rostyslav Druzhchenko. All rights reserved.
//
//  Instruction:
//
//    1. Create a sharable class:
//        1. Inherit the class from `ObservableObject`.
//        2. Create there a `property` and mark it `@Published`.
//    2. Add to environment:
//        1. Add the object as a property to `SceneDelegate` and instantiate it.
//        2. Add the object to environment
//           ```let contentView = ContentView().environmentObject(transactionStore)``` in `func scene(...`.
//    3. Add to two separate views the object as a property:
//       ```@EnvironmentObject var property: ClassName```
//
//    Enjoy.

import UIKit
import SwiftUI

class SceneDelegate: UIResponder, UIWindowSceneDelegate {

    var window: UIWindow?

    let textStore = TextStore()

    func scene(_ scene: UIScene,
               willConnectTo session: UISceneSession,
               options connectionOptions: UIScene.ConnectionOptions) {

        let contentView = ContentView().environmentObject(textStore)

        if let windowScene = scene as? UIWindowScene {
            let window = UIWindow(windowScene: windowScene)
            window.rootViewController = UIHostingController(rootView: contentView)
            self.window = window
            window.makeKeyAndVisible()
        }
    }
}

// MARK: - The environment object

class TextStore: ObservableObject {

    @Published var text = "default text"
}

// MARK: - Views

struct ContentView: View {

    var body: some View {

        TabView {
            FirstView()
                .tabItem {
                    Image(systemName: "list.dash")
                    Text("First")
            }
            SecondView()
                .tabItem {
                    Image(systemName: "list.dash")
                    Text("Second")
            }

        }
    }
}

struct FirstView: View {

    @State var label: String = ""

    @EnvironmentObject var textStore: TextStore

    var body: some View {

        VStack {

            TextField("type something", text: $label)
                .textFieldStyle(RoundedBorderTextFieldStyle())
                .padding()

            Button(action: action()) {
                Text("Save")
            }
        }
    }

    // MARK: - Private

    private func action() -> () -> Void {
        {
            self.textStore.text = self.label
            print("Saved")
        }
    }
}

struct SecondView: View {

    @EnvironmentObject var textStore: TextStore

    var body: some View {
        Text(textStore.text)
    }
}