StateLifetime.swift

//
//  ContentView.swift
//  Shared
//
//  Created by Chris Eidhof on 28.03.22.
//

import SwiftUI

struct Item: View {
    var id: Int
    @State private var counter = 0
    var body: some View {
        VStack {
            Text("Item \(id)")
            Button("Counter: \(counter)") {
                counter += 1
            }
        }
    }
}

struct ItemWrapper: View {
    var id: Int
    
    var body: some View {
        ZStack {
            Item(id: id)
        }
    }
}

final class MyObject: ObservableObject {
    init() { print("Allocating") }
}

struct StateObjectItemTest: View {
    @StateObject private var object = MyObject()
    let body = Text("Hello")
}

struct StateItemTest: View {
    @State var item: Int = {
        print("Initing")
        return 0
    }()
    let body = Text("Hello")
}

struct ContentView: View {
    var body: some View {
        NavigationView {
            VStack {
                NavigationLink("State Objects") {
                    List(0..<1000) { id in
                        StateObjectItemTest()
                    }
                }
                NavigationLink("State Values") {
                    List(0..<1000) { id in
                        StateItemTest()
                    }
                }
                NavigationLink("Indirect State") {
                    List(0..<1000) { id in
                        ItemWrapper(id: id)
                    }
                }
                NavigationLink("Direct State") {
                    List(0..<1000) { id in
                        Item(id: id)
                    }
                }
            }
        }
    }
}