Question

我正在尝试找出构建绑定到UserDefaults的简单设置屏幕的最佳方法。

基本上，我有一个Toggle，我想要：

每次更改此Toggle时都要保存的UserDefault值（UserDefault应该是事实的来源）
切换始终显示UserDefault的值

我已经看过许多SwiftUI WWDC会话，但是我仍然不确定如何使用Combine和SwiftUI中可用的不同工具来设置所有内容。我目前的想法是应该使用BindableObject，以便可以使用hat封装许多不同的设置。

我想我很亲密，因为它几乎可以按预期工作，但是行为却不一致。

当我在设备上构建并运行它时，我将其打开并打开Toggle，然后，如果我向上或向下滚动视图一点，则该开关将切换回关闭状态（好像实际上并没有在UserDefaults中保存该值）

但是，如果我打开开关，请离开应用程序，然后稍后再打开，就像它记住了设置一样。

有什么建议吗？我发布此邮件的目的是希望它能对SwiftUI和Combine的新手有所帮助，因为我找不到与此主题相关的任何类似问题。

import SwiftUI
import Combine

struct ContentView : View {

    @ObjectBinding var settingsStore = SettingsStore()

    var body: some View {
        NavigationView {
            Form {
                Toggle(isOn: $settingsStore.settingActivated) {
                    Text("Setting Activated")
                }
            }
        }.navigationBarTitle(Text("Settings"))
    }
}

class SettingsStore: BindableObject {

    var didChange = NotificationCenter.default.publisher(for: .settingsUpdated).receive(on: RunLoop.main)

    var settingActivated: Bool {
        get {
            UserDefaults.settingActivated
        }
        set {
            UserDefaults.settingActivated = newValue
        }
    }
}

extension UserDefaults {

    private static var defaults: UserDefaults? {
        return UserDefaults.standard
    }

    private struct Keys {
        static let settingActivated = "SettingActivated"
    }

    static var settingActivated: Bool {
        get {
            return defaults?.value(forKey: Keys.settingActivated) as? Bool ?? false
        }
        set {
            defaults?.setValue(newValue, forKey: Keys.settingActivated)
        }
    }
}

extension Notification.Name {
    public static let settingsUpdated = Notification.Name("SettingsUpdated")
}

Answer 1

在this video by azamsharp和this tutorial by Paul Hudson的帮助下，我已经能够产生一个绑定到UserDefaults的切换，并立即显示您已为其分配的更改。

现场代表：

在“ window”变量下添加这一行代码

var settingsStore = SettingsStore()

并修改window.rootViewController以显示此内容

window.rootViewController = UIHostingController(rootView: contentView.environmentObject(settingsStore))

SettingsStore：

import Foundation

class SettingsStore: ObservableObject {
    @Published var isOn: Bool = UserDefaults.standard.bool(forKey: "isOn") {
        didSet {
            UserDefaults.standard.set(self.isOn, forKey: "isOn")
        }
    }
}

SettingsStoreMenu

如果愿意，请创建一个名为this的SwiftUI视图并粘贴：

import SwiftUI

struct SettingsStoreMenu: View {
    
    @ObservedObject var settingsStore: SettingsStore
    
    var body: some View {
        Toggle(isOn: self.$settingsStore.isOn) {
            Text("")
        }
    }
}

最后但并非最不重要

别忘了从任何主视图中将SettingsStore注入到SettingsStoreMenu，例如

import SwiftUI

struct MainView: View {
        
    @EnvironmentObject var settingsStore: SettingsStore

    @State var showingSettingsStoreMenu: Bool = false

    
    var body: some View {
        HStack {
            Button("Go to Settings Store Menu") {
                    self.showingSettingsStoreMenu.toggle()
            }
            .sheet(isPresented: self.$showingSettingsStoreMenu) {
                    SettingsStoreMenu(settingsStore: self.settingsStore)
            }
        }
    }
}

（或您想要的其他方式。）

Answer 2

Swift 5.1发生了很多变化。 BindableObject已被完全弃用。此外，PassthroughSubject中也发生了重大变化。

对于任何想使它起作用的人，下面是相同的工作示例。我已经重复使用了“ gohnjanotis”的代码来简化它。

import SwiftUI
import Combine

struct ContentView : View {

    @ObservedObject var settingsStore: SettingsStore

    var body: some View {
        NavigationView {
            Form {
                Toggle(isOn: $settingsStore.settingActivated) {
                    Text("Setting Activated")
                }
            }.navigationBarTitle(Text("Settings"))
        }
    }
}

class SettingsStore: ObservableObject {

    let willChange = PassthroughSubject<Void, Never>()

    var settingActivated: Bool = UserDefaults.settingActivated {
        willSet {

            UserDefaults.settingActivated = newValue

            willChange.send()
        }
    }
}

extension UserDefaults {

    private struct Keys {
        static let settingActivated = "SettingActivated"
    }

    static var settingActivated: Bool {
        get {
            return UserDefaults.standard.bool(forKey: Keys.settingActivated)
        }
        set {
            UserDefaults.standard.set(newValue, forKey: Keys.settingActivated)
        }
    }
}

Answer 3

此接缝可以很好地工作：

enum BackupLocalisations: String, CaseIterable, Hashable, Identifiable {
    case iPhone = "iPhone"
    case iCloud = "iCloud"
    
    var name: String {
        return self.rawValue
    }
    var id: BackupLocalisations {self}
}

enum Keys {
    static let iCloudIsOn = "iCloudIsOn"
    static let backupLocalisation = "backupLocalisation"
    static let backupsNumber = "backupsNumber"
}

    class SceneDelegate: UIResponder, UIWindowSceneDelegate {
    
    var window: UIWindow?
    var settings = Settings()

…/…
    let contentView = ContentView()
            .environmentObject(settings)
… }

class Settings: ObservableObject {
    @Published var iCloudIsOn: Bool = UserDefaults.standard.bool(forKey: Keys.iCloudIsOn) {
        didSet { UserDefaults.standard.set(self.iCloudIsOn, forKey: Keys.iCloudIsOn) }
    }
    
    @Published var backupLocalisation: String = UserDefaults.standard.object(forKey: Keys.backupLocalisation) as? String ?? "iPhone" {
        didSet { UserDefaults.standard.set(self.backupLocalisation, forKey: Keys.backupLocalisation) }
    }
    
    @Published var backupsNumber: Int = UserDefaults.standard.integer(forKey: Keys.backupsNumber) {
        didSet { UserDefaults.standard.set(self.backupsNumber, forKey: Keys.backupsNumber) }
    }
}

struct ContentView: View {
    @ObservedObject var settings: Settings

    var body: some View {
        NavigationView {
            Form {
                Section(footer: Text("iCloud is \(UserDefaults.standard.bool(forKey: Keys.iCloudIsOn) ? "on" : "off")")) {
                    Toggle(isOn: self.$settings.iCloudIsOn) { Text("Use iCloud") }
                }
                Section {
                    Picker(selection: $settings.backupLocalisation, label: Text("\(self.settings.backupsNumber) sauvegarde\(self.settings.backupsNumber > 1 ? "s" : "") sur").foregroundColor(Color(.label))) {
                        ForEach(BackupLocalisations.allCases) { b in
                            Text(b.name).tag(b.rawValue)
                        }
                    }
                    
                    Stepper(value: self.$settings.backupsNumber) {
                        Text("Nombre de sauvegardes")
                    }
                }
            }.navigationBarTitle(Text("Settings"))
            
        }
    }
}

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

Xcode 11.3.1

Answer 4

尝试类似这样的方法。您也可以考虑使用EnvironmentObject代替每个this answer的ObjectBinding。

import Foundation

@propertyWrapper
struct UserDefault<Value: Codable> {
    let key: String
    let defaultValue: Value

    var value: Value {
        get {
            return UserDefaults.standard.object(forKey: key) as? Value ?? defaultValue
        }
        set {
            UserDefaults.standard.set(newValue, forKey: key)
        }
    }
}

使用对象绑定，该切换将使用键myBoolSetting将用户默认设置为true / false。您可以在Text视图的文本中看到当前值。

import Combine
import SwiftUI

final class SettingsStore: BindableObject {
    let didChange = PassthroughSubject<Void, Never>()

    @UserDefault(key: "myBoolSetting", defaultValue: false)
    var myBoolSetting: Bool {
        didSet {
            didChange.send()
        }
    }
}


struct ContentView : View {
    @ObjectBinding var settingsStore = SettingsStore()

    var body: some View {
        Toggle(isOn: $settingsStore.myBoolSetting) {
            Text("\($settingsStore.myBoolSetting.value.description)")
        }
    }
}

Answer 5

我看到的一个问题是您使用了错误的API来从UserDefaults设置/获取值。您应该使用：

static var settingActivated: Bool {
    get {
        defaults?.bool(forKey: Keys.settingActivated) ?? false
    }
    set {
        defaults?.set(newValue, forKey: Keys.settingActivated)
    }
}

Answer 6

这是经过一些试验后我想到的，使用PassthroughSubject而不是尝试对通知进行操作。它似乎可以一致且按预期工作。

我猜测可能有一些Swift或SwiftUI技术可以简化此操作，因此请指出其他有关如何执行此类操作的想法。

import SwiftUI
import Combine

struct ContentView : View {

    @ObjectBinding var settingsStore: SettingsStore

    var body: some View {
        NavigationView {
            Form {
                Toggle(isOn: $settingsStore.settingActivated) {
                    Text("Setting Activated")
                }
            }.navigationBarTitle(Text("Settings"))
        }
    }
}

class SettingsStore: BindableObject {

    let didChange = PassthroughSubject<Void, Never>()

    var settingActivated: Bool = UserDefaults.settingActivated {
        didSet {

            UserDefaults.settingActivated = settingActivated

            didChange.send()
        }
    }
}

extension UserDefaults {

    private struct Keys {
        static let settingActivated = "SettingActivated"
    }

    static var settingActivated: Bool {
        get {
            return UserDefaults.standard.bool(forKey: Keys.settingActivated)
        }
        set {
            UserDefaults.standard.set(newValue, forKey: Keys.settingActivated)
        }
    }
}

Answer 7

您可以扩展@Published属性包装器以将值存储在UserDefaults中（如this answer中所建议的那样）：

private var cancellables = [String: AnyCancellable]()

extension Published {
    init(defaultValue: Value, key: String) {
        let value = UserDefaults.standard.object(forKey: key) as? Value ?? defaultValue
        self.init(initialValue: value)
        cancellables[key] = projectedValue.sink { val in
            UserDefaults.standard.set(val, forKey: key)
        }
    }
}

这是基于发布的问题的示例：

import SwiftUI
import Combine

struct ContentView : View {
    @ObservedObject var settingsStore = SettingsStore()

    var body: some View {
        NavigationView {
            Form {
                Toggle(isOn: $settingsStore.settingActivated) {
                    Text("Setting Activated")
                }
            }.navigationBarTitle(Text("Settings"))
        }
    }
}

class SettingsStore: ObservableObject {
    @Published(defaultValue: false, key: "SettingActivated")
    var settingActivated: Bool
}

UserDefaults在SwiftUI中使用Toggle进行绑定

7 个答案: