SwiftUI：如果在后台任务后设置，NavigationLink 不显示动画

Question

我正在尝试将新的 async/await 并发代码与 SwiftUI 视图结合使用，以便在单击按钮后加载一些基本的异步数据，以显示微调器视图，并在完成后过渡到新页面.我使用枚举来标记视图的状态，并将其与 NavigationLink 一起使用以前进到新视图。这有效，并在 'pushing' 到下一个视图之前显示 'loading' 文本视图一秒钟，但是在推送新视图时没有动画。这是我使用的代码：

import SwiftUI

enum ContinueActionState: Int {
    case ready = 0
    case showProgressView = 1
    case pushToNextPage = 2
    case readingError = 3
    case error = 4
}


struct ContentView: View {
    
    @State var actionState: ContinueActionState? = .ready
    
    var body: some View {
        
        NavigationView {
            VStack {
            
                Text("Test the Button!")
                    
                if (actionState == .showProgressView) {
                    ProgressView("Loading Data")
                    
                } else if (actionState == .error || actionState == .readingError) {
                    Text("Error in loading something")
                }
                else {
                    NavigationLink(destination: DetailPageView(), tag: .pushToNextPage, selection: $actionState) {
                        
                        Button(action: {
                            
                            Task {
                                print("on buttonClick isMain =\(Thread.isMainThread)")
                                self.actionState = .showProgressView
                                await self.startProcessingData()
                                //self.actionState = .pushToNextPage // animation works if only this is used
                            }
                        }) {
                            Text("Continue")
                        }
                        .tint(.blue)
                        .buttonStyle(.borderedProminent)
                        .buttonBorderShape(.roundedRectangle(radius: 5))
                        .controlSize(.large)
                         
                    }
                }
            }.navigationTitle("Test Async")
        }
    }
    
    func startProcessingData() async {
        
        Task.detached {
            print("startProcessingData isMain =\(Thread.isMainThread)")
            try await Task.sleep(nanoseconds: 1_000_000_000)

            //await MainActor.run {
                self.actionState = .pushToNextPage
            //}
        }
    }
}

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

struct DetailPageView: View {
    var body: some View {
        Text("Detail page")
    }
}

如果我只是放弃异步调用并在单击按钮时立即设置为 .pushToNextPage 状态，则动画效果很好。

在后台队列任务中的内容处理完成后，有什么方法可以使动画流畅地工作吗？

Answer 1

如果您将 NavigationLink 从 if 语句中移出，它对我来说很好用：

        NavigationView {
            VStack {
                
                Text("Test the Button!")
                
                NavigationLink(destination: DetailPageView(), tag: .pushToNextPage, selection: $actionState) { Text("") } // here
                
                if (actionState == .showProgressView) {
                    ProgressView("Loading Data")
                    
                } else if (actionState == .error || actionState == .readingError) {
                    Text("Error in loading something")
                }
                else {
                    
                    Button(action: {
                        Task {
                            print("on buttonClick isMain =\(Thread.isMainThread)")
                            self.actionState = .showProgressView
                            await self.startProcessingData()
                        }
                    }) {
                        Text("Continue")
                    }
                    .tint(.blue)
                    .buttonStyle(.borderedProminent)
                    .buttonBorderShape(.roundedRectangle(radius: 5))
                    .controlSize(.large)
                    
                }
            }.navigationTitle("Test Async")
        }

SwiftUI：如果在后台任务后设置，NavigationLink 不显示动画

SwiftUI: NavigationLink doesn't show animation if setting after background task

swiftui

async-await

swift-concurrency