iOS16中ScrollView的refreshable修饰符为何会取消异步任务？

我正在开发适配iOS 16的应用，尝试在ScrollView上使用refreshable修饰符，但下拉刷新手势过程中异步任务会被取消。

复现代码 #

ExploreViewModel.swift #

class ExploreViewModel: ObservableObject {
    
    @Published var randomQuotes: [Quote] = []
    
    init() {
        Task {
            await loadQuotes()
        }
    }
     
    @MainActor
    func loadQuotes() async {
         
        let quotesURL = URL(string: "https://type.fit/api/quotes")!
        
        do {
            let (data, urlResponse) = try await URLSession.shared.data(from: quotesURL)
            guard let response = urlResponse as? HTTPURLResponse else { print("no response"); return}
            
            if response.statusCode == 200 {
                let quotes =  try JSONDecoder().decode([Quote].self, from: data)
                randomQuotes.append(contentsOf: quotes)
            }
        } catch {
            debugPrint(error)
            debugPrint(error.localizedDescription)
        }
    }
    
    func clearQuotes() {
        randomQuotes.removeAll()
    }
}

ContentView.swift #

import SwiftUI

struct ContentView: View {
    
    @StateObject private var exploreVM = ExploreViewModel()
    
    var body: some View {
        
        NavigationStack {
            ExploreView()
                .environmentObject(exploreVM)
                .refreshable {
                    exploreVM.clearQuotes()
                    await exploreVM.loadQuotes()
                }
        }
    }
}

ExploreView.swift #

import SwiftUI

struct ExploreView: View {
    
    @EnvironmentObject var exploreVM: ExploreViewModel
 
    var body: some View {
        ScrollView {
            VStack {
                LazyVGrid(columns: [GridItem(.adaptive(minimum: 140.0), spacing: 24.0)], spacing: 24.0) {
                    ForEach(exploreVM.randomQuotes) { quote in
                        VStack(alignment: .leading) {
                            Text("\(quote.text ?? "No Text")")
                                .font(.headline)
                            Text("\(quote.author ?? "No Author")")
                                .font(.caption)
                        }
                        .frame(minWidth: 0, maxWidth: .infinity)
                        .frame(height: 144.0)
                        .border(Color.red, width: 2.0)
                        
                    }

                }
            }
            .padding()
            .navigationTitle("Explore")
        }
 
    }
}

问题演示与报错 #

下拉刷新手势过程中任务被取消的演示：

控制台报错截图：

问题核心是refreshable修饰符的闭包任务会绑定到下拉手势生命周期，用户松开手指时系统会自动取消闭包内的异步任务，导致网络请求中断。以下是两种解决方式：

方式1：在ViewModel中维护独立刷新任务 #

修改ExploreViewModel，新增独立的刷新逻辑，脱离refreshable的取消上下文：

class ExploreViewModel: ObservableObject {
    
    @Published var randomQuotes: [Quote] = []
    private var refreshTask: Task<Void, Error>? // 新增任务变量
    
    init() {
        Task {
            await loadQuotes()
        }
    }
     
    @MainActor
    func loadQuotes() async {
        // 原加载逻辑不变
        let quotesURL = URL(string: "https://type.fit/api/quotes")!
        
        do {
            let (data, urlResponse) = try await URLSession.shared.data(from: quotesURL)
            guard let response = urlResponse as? HTTPURLResponse else { print("no response"); return}
            
            if response.statusCode == 200 {
                let quotes =  try JSONDecoder().decode([Quote].self, from: data)
                randomQuotes.append(contentsOf: quotes)
            }
        } catch {
            debugPrint(error)
            debugPrint(error.localizedDescription)
        }
    }
    
    func clearQuotes() {
        randomQuotes.removeAll()
    }
    
    // 新增独立刷新方法
    func refreshQuotes() {
        refreshTask?.cancel() // 取消未完成的旧任务
        refreshTask = Task {
            await MainActor.run { self.clearQuotes() }
            await loadQuotes()
        }
    }
}

更新ContentView的refreshable闭包：

.refreshable {
    exploreVM.refreshQuotes()
    await exploreVM.refreshTask?.value // 可选：等待任务完成
}

方式2：在refreshable中使用Task.detached #

无需修改ViewModel，直接在闭包内用Task.detached启动不受取消影响的任务：

.refreshable {
    await Task.detached {
        await MainActor.run {
            self.exploreVM.clearQuotes()
        }
        await self.exploreVM.loadQuotes()
    }.value
}

内容的提问来源于stack exchange，提问作者Jobie J