从网络请求更新 EnvironmentObject 后，NavigationLink 在嵌套的 ScrollView 中不起作用

Posted 2023-02-23

【中文标题】从网络请求更新 EnvironmentObject 后，NavigationLink 在嵌套的 ScrollView 中不起作用

【英文标题】：NavigationLink doesn't work in nested ScrollView after EnvironmentObject update from network request

【发布时间】：2021-11-26 06:09:30

【问题描述】：

我有两个用于 navigationView、Dashboard 和 Userscreen 的选项卡。

Userscreen用于通过网络请求获取用户信息，dashboard是根据用户信息通过网络请求显示信息，这里用户信息就是环境对象。

更新用户信息后，我可以查看仪表板属性，但单击导航链接不起作用。 经过一番测试，我发现 ScrollView -> ScrollView(.horizo​​ntal) -> NavigationLink 下的导航链接（根据用户信息显示）不起作用，但 VStack -> ScrollView( 下的导航链接（根据用户信息显示） .horizo​​ntal) -> NavigationLink 表现良好。

我想知道我是否在实现中遗漏了什么，或者我想问一下它是否是 XCode 的现有错误？

编辑：更新代码

再次编辑：请参考下面@workingdog的解决方案，整个问题只是由一个简单的愚蠢错误引起的，即没有声明正确的状态/环境对象。

import SwiftUI
import Kingfisher
import Alamofire

struct ExampleView: View 
@StateObject var userInfoManager = UserInfoManagerExample()

var body: some View 
    NavigationView 
        TabView ()
            DashboardScreenExample()
                .environmentObject(userInfoManager)
                .tabItem
                    Text("Dashboard")
                
            LoginScreenExample()
                .environmentObject(userInfoManager)
                .tabItem
                    Text("UpdateInfo")
                
        
        .navigationBarTitleDisplayMode(.inline)
    
    .navigationViewStyle(StackNavigationViewStyle())



struct DashboardScreenExample: View 

@EnvironmentObject var userInfoManager : UserInfoManagerExample
@State var please : Bool = false

init()
   Theme.navigationBarColors(background: UIColor(viewProperties.themered), titleColor: .white)


var viewProperties = ViewProperties()

var body: some View 
    if(userInfoManager.shouldShowDashboard)
        ScrollView//Switch this ScrollView to VStack make Navigation Link work again
            //I had other screens too, but screen below is the one causing problem
            DashboardContentExample()
        
    else
        ProgressView().onAppearuserInfoManager.shouldShowDashboard = true
    



struct DashboardContentExample: View 

@EnvironmentObject var userInfoManager : UserInfoManagerExample
@ObservedObject var dashboardList = DashboardConfigRequestExample()

func loadRequest()
    dashboardList.loadData(passedLanguage: userInfoManager.preferenceLangauge)


//View start from here
var body: some View 
    if(dashboardList.dashboardConfig.count == 0)
        ProgressView()
            .onAppear
                loadRequest()
            
    else
        ScrollView(.horizontal)
            LazyHStack
                //Here is the NavigationLink not working
                NavigationLink(destination: EmptyView())
                    Text("Hello")
                
            
        
    



struct LoginScreenExample: View 

let usernameLoginRequest = UsernameLoginRequestExample()
@EnvironmentObject var userInfoManager : UserInfoManagerExample
@State var loginClicked : Bool = false

var body: some View 
    VStack(alignment: .leading)
        if(userInfoManager.isLogin)
            Text("You have logged in.")
                .onAppear
                    loginClicked = false
                
        
        else
            ZStack
                VStack
                    Spacer()
                    //the username and password had to be entered
                    Button(action:clickLogin(forUsername: "iamusername", andPassword: "iampassword"))
                        Text("Sign In")
                    
                    Spacer()
                
                if(loginClicked)
                    ProgressView()
                
                
            
        
    


func clickLogin(forUsername: String, andPassword: String)
    loginClicked.toggle()
    usernameLoginRequest.loadData(forUsername: forUsername, andPassword: andPassword, andUserInfo: userInfoManager)



class UserInfoManagerExample : ObservableObject

@Published var isLogin: Bool = false
@Published var username: String = ""
@Published var password: String = ""
@Published var preferenceLangauge: String = "en"
@Published var shouldShowDashboard = true

init()


func updateCredential(forUsername: String, andPassword: String)
    username = forUsername
    password = andPassword



struct UsernameLoginRequestExample

func loadData(forUsername: String, andPassword: String, andUserInfo: UserInfoManagerExample)
    let request_url = "This is the request url"
    let request_parameters = getUsernameLoginParameter(withUsername: forUsername, andPassword: andPassword)
    
    AF
    .request(request_url, method: .post, parameters: request_parameters, encoding: JSONEncoding.default ).responseJSON
        responses
        in
        debugPrint(responses)
        
        switch responses.result
        case .success:
            do 
                andUserInfo.shouldShowDashboard = false
                andUserInfo.updateCredential(forUsername: forUsername, andPassword: andPassword)
                andUserInfo.isLogin = true
            
        case let .failure(error):
            print(error)
        
    


func getUsernameLoginParameter(withUsername : String, andPassword : String) -> [String : String]
    var parameters : [String : String] = [String : String]()
    parameters.updateValue(withUsername, forKey: "username")
    parameters.updateValue(andPassword, forKey: "password")
    
    var device_id : String
    
    if(UIDevice.current.identifierForVendor != nil)
        device_id = UIDevice.current.identifierForVendor!.uuidString
    else
        device_id = ""
    
    
    parameters.updateValue(device_id, forKey:"device_id")
    
    return parameters



class DashboardConfigRequestExample : ObservableObject
@Published var dashboardConfig = [DashboardConfigExample]()

func loadData(passedLanguage : String)
    let request_url = "This is request url"
          
    let request_parameters = getDashboardConfigParameter(passedLanguage: passedLanguage)
    
    AF
    .request(request_url, method:.post, parameters: request_parameters)
    .responseJSON
        
        responses in
        
        switch responses.result 
            case .success:
                guard
                    let data = responses.data
                else  return 
                do 
                    let configResponse = try JSONDecoder().decode(DashboardConfigDataExample.self, from: data)
                        self.dashboardConfig = configResponse.list ?? []
                 catch 
                    print(error)
                
            case let .failure(error):
                print(error)
        
    


func getDashboardConfigParameter(passedLanguage: String) -> [String:String]
    var parameters : [String:String] = [String:String]()
    parameters.updateValue(passedLanguage, forKey: "language")
    return parameters



struct DashboardConfigDataExample : Decodable
public var status: String?
public var list: [DashboardConfigExample]?


struct DashboardConfigExample: Encodable & Codable 
let background_image: String?
let background_color: String?

【问题讨论】：

您的代码在我的测试中似乎对我有用。单击NavigationLinks 可以工作。在 macos 12.1-beta 上，使用 xcode 13.2-beta，针对 ios 15 和 macCatalyst 12。

感谢您的回复，如果 @Published var 在没有网络请求的情况下更新，我的代码可以正常工作。代码中有两个cmet会从我的后端执行异步网络请求，依次更新环境对象，涉及NavigationLinks的屏幕需要再次更新，然后NavigationLinks在请求后将不起作用。但是用VStack 替换ScrollView 以某种方式使NavigationLinks 起作用。

因此，您向我们展示的代码并不是给您带来任何问题的代码。你能告诉我们可以复制你的问题的代码吗？

我改了代码，但是去掉了网络请求参数和url，谢谢。

【参考方案1】：

尝试替换

@ObservedObject var infoRequest = InfoRequest()

在Dashboard 中

@StateObject var infoRequest = InfoRequest()

EDIT1：根据新代码。

尝试移动@ObservedObject var dashboardList = DashboardConfigRequestExample() 的DashboardContentExample 进入ExampleView 为@StateObject。类似于以下示例代码：

struct ExampleView: View 
    @StateObject var userInfoManager = UserInfoManagerExample()
    @StateObject var dashboardList = DashboardConfigRequestExample()  // <-- here
    
    var body: some View 
        NavigationView 
            TabView ()
                DashboardScreenExample().tabItem Text("Dashboard")
                LoginScreenExample().tabItem Text("UpdateInfo")
            .navigationBarTitleDisplayMode(.inline)
        
        .environmentObject(userInfoManager)  // <-- here
        .environmentObject(dashboardList)    // <-- here
        .navigationViewStyle(StackNavigationViewStyle())
    


struct DashboardContentExample: View 
    
    @EnvironmentObject var userInfoManager : UserInfoManagerExample
    @EnvironmentObject var dashboardList: DashboardConfigRequestExample  // <-- here
    
    func loadRequest()
        dashboardList.loadData(passedLanguage: userInfoManager.preferenceLangauge)
    
    
    //View start from here
    var body: some View 
        if(dashboardList.dashboardConfig.count == 0)
            ProgressView()
                .onAppear
                    loadRequest()
                
        else
            ScrollView(.horizontal)
                LazyHStack
                    //Here is the NavigationLink not working
                    NavigationLink(destination: Text("Hello destination"))  // <-- here for testing
                        Text("Hello")
                    
                
            
        
    

【讨论】：

我改了，导航链接好像还是不行。顺便说一句，我已经将代码编辑为真正引起我问题的代码，感谢您帮助@workingdog！

根据您的新代码更新了我的答案。

抱歉@workingdog 回复晚了……即使我根据更新后的答案添加了新的@stateobject 和@environmentobject，导航链接也无法正常工作，但无论如何感谢您提供帮助！但是navigation links有一个奇怪的行为是，它们在点击时没有响应，但在切换标签后，之前链接的屏幕会立即弹出。

原来是我把环境对象放到了错误的屏幕上，非常感谢！