swiftUI：设置更改后更新文本

Question

[编辑(1) 以反映posting of streamlined app 以说明问题：]。
[编辑（2）：完全删除 EnvironmentObject 和应用程序现在可以工作了！不理解为什么会刷新正文，因为没有修改 @State 变量...文本末尾的代码]

我正在编写一个应用程序，它在某些时候会根据一组规则显示一些与 2 个数组的内容相关的文本。这些规则可以在设置视图中设置，作为用户的偏好。 因此，当用户更改他希望在“设置”中应用的规则时，需要重新评估该文本。
但当然，事情并不那么容易。
我在主 ContentView 上将设置视图显示为模态，当我关闭该模态时，不会重绘 ContentView 的主体...

我使用 @Published 变量创建了一个 EnvironmentObject，以跟踪所有用户偏好（也写入 UserDefaults），并与我的 ContentView 和 SettingsView 共享该 @EnvironmentObject，希望成为一个被观察的对象，它的更改会触发我的 ContentView 的刷新。

不是这样……

有什么想法可以帮助我继续前进吗？任何指针将不胜感激（再次！）。

Posted app on GitHub 具有以下架构：

一个appState环境对象，
ContentView 显示一组文本，具体取决于在 一个settingsView

UserDefaults 在AppDelegate 中初始化。

感谢您对此的任何帮助...

内容视图：

import SwiftUI
struct ContentView: View {

  @State var modalIsPresented = false // The "settingsView" modally presented as a sheet

  @State private var modalViewCaller = 0 // This triggers the appropriate modal (only one in this example)

    var body: some View {

        NavigationView {
            VStack {
                Spacer()
                    VStack {
                    Text(generateStrings().text1)
                        .foregroundColor(Color(UIColor.systemGreen))
                    Text(generateStrings().text2)
                    } // end of VStack
                        .frame(maxWidth: .infinity, alignment: .center)
                        .lineLimit(nil) // allows unlimited lines
                        .padding(.all)
                Spacer()
            } // END of main VStack
            .onAppear() {
                self.modalViewCaller = 0
            }
            .navigationBarTitle("Test app", displayMode: .inline)
            .navigationBarItems(leading: (
                Button(action: {
                    self.modalViewCaller = 6 // SettingsView
                    self.modalIsPresented = true
                }
                    ) {
                        Image(systemName: "gear")
                            .imageScale(.large)
                     }
            ))
        } // END of NavigationView
        .sheet(isPresented: $modalIsPresented, content: sheetContent)
        .navigationViewStyle(StackNavigationViewStyle()) // This avoids dual column on iPad

    } // END of var body: some View

  // MARK: @ViewBuilder func sheetContent() :

    @ViewBuilder func sheetContent() -> some View {

        if modalViewCaller == 6 {
            SettingsView()
            }
    } // END of func sheetContent


    // MARK: generateStrings() : -

    func generateStrings() -> (text1: String, text2: String, recapText: String, isHappy: Bool) { // minimumNumberOfEventsCheck

        var myBool = false
        var aString = "" // The text 1 string
        var bString = "" // The text 2 string
        var cString = "" // The recap string

        if UserDefaults.standard.bool(forKey: kmultiRules) { // The user chose the dual rules option
            let ruleSet = UserDefaults.standard.integer(forKey: kruleSelection) + 1
            aString = "User chose 2 rules option"
            bString = "User chose rule set # \(ruleSet)"
            myBool = true
            print("isDualRules true loop : generateStrings was called at \(Date().debugDescription)")
            cString = "Dual rules option, user chose rule set nb \(ruleSet)"
        }
            else // The user chose the single rule option
        {
            aString = "User chose single rule option"
            bString = "User had no choice : there is only one set of rules !"
            myBool = false
            print("isDualRules false loop : generateStrings was called at \(Date().debugDescription)")
            cString = "Single rule option, user chose nothing."
        }


            return (aString, bString, cString, myBool)
    } // End of func generatestrings() -> String

}

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

    }
}

设置视图：

import SwiftUI
import UIKit

struct SettingsView: View {

    @Environment(\.presentationMode) var presentationMode // in order to dismiss the Sheet

    @State public var multiRules = UserDefaults.standard.bool(forKey: kmultiRules)

    @State private var ruleSelection = UserDefaults.standard.integer(forKey: kruleSelection) // 0 is rule 1, 1 is rule 2


    var body: some View {

        NavigationView {
            List {

                Toggle(isOn: $multiRules)
                {
                    Text("more than one rule ?")
                }
                .padding(.horizontal)

                if multiRules {
                            Picker("", selection: $ruleSelection){
                                Text("rules 1").tag(0)
                                Text("rules 2").tag(1)
                            }.pickerStyle(SegmentedPickerStyle())
                            .padding(.horizontal)
                        }

            } // End of List
            .navigationBarItems(
                leading:
                Button("Done") {
                        self.saveDefaults() // We try to save once more if needed
                        self.presentationMode.wrappedValue.dismiss() // This dismisses the view
                }
            )
                .navigationBarTitle("Settings", displayMode: .inline)
        } // END of Navigation view
    } // END of some View


    func saveDefaults() {
        UserDefaults.standard.set(multiRules, forKey: kmultiRules)
        UserDefaults.standard.set(ruleSelection, forKey: kruleSelection)
    }    
}



// MARK: Preview struct

struct SettingsView_Previews: PreviewProvider {
    static var previews: some View {

        return SettingsView()
    }
}

Constants.swift 文件：

import Foundation
import SwiftUI

let kmultiRules = "two rules"
let kruleSelection = "rules selection"
let kappStateChanged = "appStateChanged"

AppDelegate：

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        // Override point for customization after application launch.

        UserDefaults.standard.register(defaults: [ // We initialize the UserDefaults
        "two rules": false,
        "rules selection": 0, // 0 is ruel 1, 1 is rule 2
        "appStateChanged": false
        ])

        return true
    }

Answer 1

如果您在两个视图中有一个具有@Published 属性的共享@EnvironmentObject，如果您从一个视图更改此类属性，则另一个将重新执行body 属性并更新视图。

创建简单的独立示例确实很有帮助 - 不仅可以在这里提问，还可以更深入地了解/了解为什么它在复杂情况下不起作用。

例如：

import SwiftUI

class TextSettings: ObservableObject {
    @Published var count: Int = 1
}

struct TextSettingsView: View {
    @EnvironmentObject var settings: TextSettings

    var body: some View {
        Form {
            Picker(selection: $settings.count, label:
                Text("Text Repeat Count"))
            {
                ForEach(Array(1...5), id: \.self) { value in
                    Text(String(value)).tag(value)
                }
            }
        }
    }
}

struct TextWithSettingExampleView: View {
    @EnvironmentObject var settings: TextSettings

    var body: some View {
        Text(String(repeating: "Hello ", count: Int(settings.count)))
            .navigationBarItems(trailing: NavigationLink("Settings", destination: TextSettingsView()))
    }

}

struct TextWithSettingExampleView_Previews: PreviewProvider {
    static var previews: some View {
        NavigationView {
            TextWithSettingExampleView()
        }
        .environmentObject(TextSettings())
    }
}

Answer 2

不确定我是否完全理解这个问题，但我有一个我认为可能是类似问题的问题，当从模式触发更改时，我从来没有让我的内容视图反映我观察到的对象中的更新。我通过在我观察到的对象中触发一个动作来解决/破解这个问题，当像这样解除模态时：

struct ContentView: View {
//
@State var isPresentingModal = false
var body: some View {
//
.sheet(isPresented: self.$isPresentingModal) {
                        PresentedModalView()
                            .onDisappear {
                                //Do something here
                         }
                       }
                     }
                   }