iOS 17 Observable宏实现SwiftUI状态恢复的最优方案

核心思路 #

iOS 17的@Observable宏会自动为类生成变更追踪逻辑，无需手动处理ObservableObject的objectWillChange发布者。我们可以利用这一特性，直接通过视图的变更监听或模型内部的属性监听，实现导航数据到SceneStorage的同步，替代原有的异步流监听方案。

方案1：视图内监听模型整体变更 #

直接在视图中监听NavModel实例的变化，一旦模型属性更新就同步SceneStorage。

导航模型定义

import SwiftUI

@Observable
class NavModel {
    // 导航路径示例
    var pathOne: [String] = []
    var pathTwo: [Int] = []
    
    // 生成用于存储的JSON数据
    var jsonData: Data? {
        let combinedData = ["pathOne": pathOne, "pathTwo": pathTwo]
        return try? JSONSerialization.data(withJSONObject: combinedData)
    }
}

视图实现

struct MainView: View {
    @SceneStorage("navigationData") private var storedData: Data?
    @State private var navModel = NavModel()
    
    var body: some View {
        NavigationStack(path: $navModel.pathOne) {
            // 你的导航视图内容
            Text("Home")
                .navigationDestination(for: String.self) { item in
                    Text("Detail: \(item)")
                }
        }
        .onAppear {
            // 从SceneStorage恢复导航状态
            guard let data = storedData,
                  let combined = try? JSONSerialization.jsonObject(with: data) as? [String: Any] else {
                return
            }
            navModel.pathOne = combined["pathOne"] as? [String] ?? []
            navModel.pathTwo = combined["pathTwo"] as? [Int] ?? []
        }
        .onChange(of: navModel) { _, _ in
            // 模型任何属性变化时，同步到SceneStorage
            storedData = navModel.jsonData
        }
    }
}

方案2：细粒度监听具体路径属性 #

如果不想监听整个模型实例，可以单独监听导航路径的变化，减少不必要的触发：

struct MainView: View {
    @SceneStorage("navigationData") private var storedData: Data?
    @State private var navModel = NavModel()
    
    var body: some View {
        NavigationStack(path: $navModel.pathOne) {
            // 视图内容
        }
        .onAppear {
            // 状态恢复逻辑同上
        }
        .onChange(of: navModel.pathOne) { _ in
            updateStoredData()
        }
        .onChange(of: navModel.pathTwo) { _ in
            updateStoredData()
        }
    }
    
    private func updateStoredData() {
        let combinedData = ["pathOne": navModel.pathOne, "pathTwo": navModel.pathTwo]
        storedData = try? JSONSerialization.data(withJSONObject: combinedData)
    }
}

方案3：模型内部处理属性变更 #

将状态同步逻辑封装在NavModel内部，视图只需监听最终的jsonData变化：

@Observable
class NavModel {
    private(set) var jsonData: Data?
    
    var pathOne: [String] = [] {
        didSet { updateJsonData() }
    }
    
    var pathTwo: [Int] = [] {
        didSet { updateJsonData() }
    }
    
    private func updateJsonData() {
        let combinedData = ["pathOne": pathOne, "pathTwo": pathTwo]
        jsonData = try? JSONSerialization.data(withJSONObject: combinedData)
    }
}

// 视图中只需监听jsonData
struct MainView: View {
    @SceneStorage("navigationData") private var storedData: Data?
    @State private var navModel = NavModel()
    
    var body: some View {
        NavigationStack(path: $navModel.pathOne) {
            // 视图内容
        }
        .onAppear {
            // 状态恢复逻辑同上
        }
        .onChange(of: navModel.jsonData) { newData in
            storedData = newData
        }
    }
}

方案优势 #

相比原ObservableObject+异步流的实现，这些方案更简洁直观：

• 无需手动创建objectWillChange的异步发布者和缓冲流
• 利用@Observable自动生成的变更追踪，减少样板代码
• 可根据需求选择整体监听或细粒度监听，灵活性更高

内容的提问来源于stack exchange，提问作者dehlen