在重新打开应用/预览之前，视图不会更新

Question

问题：如何在不重新启动应用程序/预览的情况下从Login()返回到Home()？我有一种感觉，这与变量不是@State有关，但我不知道如何将@State添加到全局变量中。

这是我的代码：

import SwiftUI
var isLoggedIn:Bool {
get {
// Get the standard UserDefaults as "defaults"
let defaults = UserDefaults.standard
// Makes the "welcomeString" variable whatever the saved value for "welcome_string" is
return defaults.bool(forKey: "isLoggedIn")
}
set (newValue) {
// Get the standard UserDefaults as "defaults"
let defaults = UserDefaults.standard
// Saves what the "welcomeString" variable was just set to as the saved value for "welcome_string"
defaults.set(newValue, forKey: "isLoggedIn")
}
}

struct ContentView: View {
var body: some View {
if isLoggedIn {
Home()
} else {
Login()
}
}
}
struct Login: View {
var body: some View {
Button(action: {
isLoggedIn = true
}) {
Text("Click to login")
}
}
}
struct Home: View {
private enum Tab: Hashable {
case schedule
case messaging
case home
case resources
case settings
}
@State private var selectedTab: Tab = .home
var body: some View {
VStack {
TabView(selection: $selectedTab) {
One()
.tag(Tab.home)
.tabItem {
Label("One", systemImage: "note")
}
Two()
.tag(Tab.home)
.tabItem {
Label("Two", systemImage: "note")
}
Three()
.tag(Tab.home)
.tabItem {
Label("Three", systemImage: "note")
}
Four()
.tag(Tab.home)
.tabItem {
Label("Four", systemImage: "note")
}
}
}
}
}
struct One: View {
var body: some View {
Text("One")
}
}
struct Two: View {
var body: some View {
Text("Two")
}
}
struct Three: View {
var body: some View {
Text("Three")
}
}
struct Four: View {
var body: some View {
Button(action: {
isLoggedIn = false
}) {
Text("Logout")
}
}
}

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

Answer 1

我不知道你为什么会遇到这个简单的问题，如果一个变量没有用SwiftUI的工作方式包装，你就不能依赖它的值更新，根据你在问题中的方法，这里有第一种方法，别忘了模拟器在使用UserDefaults时并不总是正确的，所以它可能不会以应有的方式工作，然后尝试在真实设备上使用：

struct ContentView: View {

@State private var isLoggedIn: Bool = { return UserDefaults.standard.bool(forKey: "isLoggedIn") }()

var body: some View {

if (isLoggedIn) {
Home(isLoggedIn: $isLoggedIn)
}
else {
Login(isLoggedIn: $isLoggedIn)
}  
}
}
func updateLog(_ newValue: Bool) { UserDefaults.standard.set(newValue, forKey: "isLoggedIn") }

struct Login: View {

@Binding var isLoggedIn: Bool
var body: some View {
Button("Tap to login") { isLoggedIn = true; updateLog(true) }
}
}
struct Home: View {

private enum Tab: Hashable {
case schedule
case messaging
case home
case resources
case settings
}

@State private var selectedTab: Tab = .home
@Binding var isLoggedIn: Bool

var body: some View {
VStack {
TabView(selection: $selectedTab) {
One()
.tag(Tab.home)
.tabItem {
Label("One", systemImage: "note")
}
Two()
.tag(Tab.home)
.tabItem {
Label("Two", systemImage: "note")
}
Three()
.tag(Tab.home)
.tabItem {
Label("Three", systemImage: "note")
}
Four(isLoggedIn: $isLoggedIn)
.tag(Tab.home)
.tabItem {
Label("Four", systemImage: "note")
}
}
}
}
}
struct One: View {
var body: some View {
Text("One")
}
}
struct Two: View {
var body: some View {
Text("Two")
}
}
struct Three: View {
var body: some View {
Text("Three")
}
}
struct Four: View {
@Binding var isLoggedIn: Bool
var body: some View {
Button("Logout") { isLoggedIn = false; updateLog(false) }
}
}

---

第二种方式：

struct ContentView: View {
@AppStorage("isLoggedIn") var isLoggedIn: Bool = false
var body: some View {

if (isLoggedIn) {
Home()
}
else {
Login()
}
}
}
struct Login: View {
@AppStorage("isLoggedIn") var isLoggedIn: Bool = false
var body: some View {
Button("Tap to login") { isLoggedIn = true }
}
}
struct Home: View {

private enum Tab: Hashable {
case schedule
case messaging
case home
case resources
case settings
}

@State private var selectedTab: Tab = .home
@AppStorage("isLoggedIn") var isLoggedIn: Bool = false

var body: some View {
VStack {
TabView(selection: $selectedTab) {
One()
.tag(Tab.home)
.tabItem {
Label("One", systemImage: "note")
}
Two()
.tag(Tab.home)
.tabItem {
Label("Two", systemImage: "note")
}
Three()
.tag(Tab.home)
.tabItem {
Label("Three", systemImage: "note")
}
Four()
.tag(Tab.home)
.tabItem {
Label("Four", systemImage: "note")
}
}
}
}
}
struct One: View {
var body: some View {
Text("One")
}
}
struct Two: View {
var body: some View {
Text("Two")
}
}
struct Three: View {
var body: some View {
Text("Three")
}
}
struct Four: View {
@AppStorage("isLoggedIn") var isLoggedIn: Bool = false
var body: some View {
Button("Logout") { isLoggedIn = false }
}
}