SwiftUI 读取 http 响应代码并可以在控制台中打印它，但不会 运行 if 语句中的任何其他代码

Question

我使用 POST http 方法创建了一个基本的登录功能。凭据发送成功，服务器身份验证成功。 httpResponse.statusCode 被发送并打印到控制台中。我正在尝试发出警报 httpResponse.statusCode 是 400，如果它是 200，则加载一个新视图。这是我正在使用的代码；

Button(action: {
    let login = self.username
    let passwordstring = self.password
    guard let url = URL(string: "http://localhost:8000/account/auth/") else {return}

    let headers = [
        "Content-Type": "application/x-www-form-urlencoded",
        "cache-control": "no-cache",
        "Postman-Token": "89a81b3d-d5f3-4f82-8b7f-47edc39bb201"
    ]

    let postData = NSMutableData(data: "username=\(login)".data(using: String.Encoding.utf8)!)
    postData.append("&password=\(passwordstring)".data(using: String.Encoding.utf8)!)

    let request = NSMutableURLRequest(url: NSURL(string: "http://localhost:8000/account/auth/")! as URL,
                                      cachePolicy:.useProtocolCachePolicy, timeoutInterval: 10.0)
    request.httpMethod = "POST"
    request.allHTTPHeaderFields = headers
    request.httpBody = postData as Data

    let session = URLSession.shared
    let dataTask = session.dataTask(with: request as URLRequest, completionHandler: { (data, response, error) in
        if let httpResponse = response as? HTTPURLResponse {
            guard let data = data else {return}
            print(data)
            if httpResponse.statusCode == 200{
                DispatchQueue.main.async {
                    //Segue to new view goes here
                    print(httpResponse.statusCode)

                    AreaView().animation(.easeIn)
                }
            }else{
                if httpResponse.statusCode == 400{
                    DispatchQueue.main.async {
                        Alert(title: Text("Oops"), message: Text("Username or Password Incorrect"), dismissButton: .default(Text("Got it!")))
                        print(httpResponse.statusCode)

                    }
                }else{
                    DispatchQueue.main.async {
                        Alert(title: Text("Well Damn"), message: Text("Ay chief we have no idea what just happened but it didn't work"), dismissButton: .default(Text("Got it!")))

                    }
                }
            }
            do{

                let JSONFromServer = try JSONSerialization.jsonObject(with: data, options: [])
                let decoder = JSONDecoder()
                decoder.keyDecodingStrategy = .convertFromSnakeCase
                let tokenArray = try decoder.decode(token.self, from: data)
                print(tokenArray.token)
                UserDefaults.standard.set(tokenArray.token, forKey: "savedToken")
                let savedToken = UserDefaults.standard.object(forKey: "savedToken")
                print(savedToken)
            }catch{
                if httpResponse.statusCode == 400{
                    Alert(title: Text("Oops"), message: Text("Username or Password Incorrect"), dismissButton: .default(Text("Got it!")))

                }
                print(error)
                print(httpResponse.statusCode)
            }
        } else if let error = error {

            Alert(title: Text("Well Damn"), message: Text("Ay chief we have no idea what just happened but it didn't work"), dismissButton: .default(Text("Got it!")))

            print(error)
        }
    })
    dataTask.resume()

})//end of login function
{
    Image("StartNow 3").resizable()
        .scaledToFit()
        .padding()
}
    .padding(.horizontal, 15).offset(y: -50)

AlertView 不会弹出，AreaView() 也不会加载。在 if 语句中唯一有效的命令是 print。我进行了大量谷歌搜索以尝试找出问题所在，但 SwiftUI 太新了。控制台也不给我任何错误消息。值得注意的是，我的代码是由 PostMan 生成的。感谢任何帮助。

Answer 1

这里您需要做的基本事情是重构您的方法以适应 SwiftUI 的 声明性 性质，而不是 UIKit 的性质命令自然

• 在 UIKit 中，您必须描述让您的 UI 以某种方式显示的步骤（例如，当此事件发生时，显示此警报）。
• 在 SwiftUI 中，您描述 UI 对于任何应用程序状态应该是什么样子，然后让框架将您带到那里（例如，当应用程序处于此状态时，会发出警报正在显示）

如果您查看 Xcode 中的警告，您会看到类似“Result of 'Alert' initializer is unused”的内容。这是因为您正在创建 Alert 的实例，但它会在当前范围的末尾立即被丢弃，因为它与您的视图没有任何联系。

作为 Swift 中的简化示例UI：

struct ContentView: View {
    @State private var showingAreaView = false
    @State private var showingAlert = false
    @State private var alertTitle = ""
    @State private var alertMessage = ""

    var body: some View {
        VStack {
            Button("Login") {
                self.login()
            }

            // only show the AreaView when showingAreaView == true
            // this will be set in the completion handler
            if showingAreaView {
                AreaView()
                    .animation(.easeIn)
            }
        }
        // only present an Alert when showingAlert == true
        // this will be set in the completion handler
        .alert(isPresented: $showingAlert) { () -> Alert in
            Alert(title: Text(alertTitle),
                  message: Text(alertMessage),
                  dismissButton: .default(Text("Got it!")))
        }
    }

    func login() {

        // setting up request, session, dataTask, etc.
        ...

            if httpResponse.statusCode == 200 {
                // if request is successful, show AreaView
                DispatchQueue.main.async {     
                    // do something with data here               
                    self.showingAreaView = true
                }
            } else if httpResponse.statusCode == 400 {
                // if request is unsuccessful, show Alert
                DispatchQueue.main.async {
                    self.alertTitle = "Oops"
                    self.alertMessage = "Username or Password Incorrect"
                    self.showingAlert = true
                }
            }

        ...

        dataTask.resume()
    }
}