SwiftUI @Published 变量未更新

Question

我有一个带有名为 userData 的 @Published 变量的类。当在此类中调用函数 fbLogic.getUserData() 时，它会使用从对 Firestore 数据库的调用中填充的数据更新 userData 数组。

问题是这个发布的变量在访问它的视图中没有更新。或者更重要的是，这些函数不会等到 Firestore 调用完成后才访问变量。所以 BarGraphView() 是用空的 reports[] 数组调用的，并且这个数组不会被 convertToReports() 调用更新，因为 convertToReports() 是用一个空的 userData 数组调用的，因为 fbLogic.getUserData() 还没有完成检索Firebase 数据。希望代码能更好地解释它。

这是引用数组的视图。

struct StatsView: View {
    let ID: String;
    @EnvironmentObject var statsController: StatsDataController
    @State var reports: [Report] = [Report]();
    @Binding var fbLogic: FirebaseLogic
    var body: some View {
 
       
        BarGraphView(selection: $selection, reports: $reports, originalReports: $originalReports).environmentObject(statsController).onAppear{
            fbLogic.userData = fbLogic.getUserData(uid: ID); //supposed to update the userData @Published var
            

            //These are called before fbLogic.userData has even been updated !!!
            self.reports = statsController.convertToReports(users: fbLogic.userData);
            print("fblogic data ", fbLogic.userData, " ", ID);};

    }

此视图在对 .getUserData() 的调用完成之前打印出“fb logic data []”，因此对 convertToReports() 的调用发生在一个空数组，而不是填充数组。

请问，我如何让该视图识别 fbLogic.userData @Pubished 数组已更新并调用 convertToReports()，并使用 POPULATED 数组重新绘制 BarGraphView。

这是 fbLogic 类的一部分，因此您可以理解对 firebase 的调用：

class FirebaseLogic: ObservableObject {
@Published var userData = [UserData]()
    
   
 func getUserData(uid: String) -> [UserData]{
            let db = Firestore.firestore()
            userData = [UserData]()
            let auth = Auth.auth();
            let currentUser = (auth.currentUser?.uid)!
            
                let data = db.collection("UserData").document(currentUser).collection("Data")    .getDocuments { [self] (snapshot, error) in
                    guard let snapshot = snapshot, error == nil else {
                     return
                   }
                   print("Number of documents fb logic get user data: \(snapshot.documents.count ?? -1)")
                   snapshot.documents.forEach({ (documentSnapshot) in
                       
                       
                    let documentData = documentSnapshot.data()
                    //CONVERT TO userObject here (removed for simplicity)
                   
                    userData.append(userObject)

                   })
                   
                 }
                
            return userData
            
        }

Answer 1

尝试使用

@ObservedObject var fbLogic: FirebaseLogic

在统计视图中。当您将数据从父视图传递到此视图时，请确保将 @ObservedObject 类型传递给 StatsView。

Answer 2

这不起作用的原因是对getDocuments() 的调用是异步的。所以当你返回映射文档的数组时（考虑使用 Codable），它仍然是空的。

这是您的代码的更新版本，它将映射的文档分配给已发布的属性。

class FirebaseLogic: ObservableObject {
  @Published var userData = [UserData]()
  func getUserData(uid: String) -> [UserData] {
    let db = Firestore.firestore()
    let localUserData = [UserData]()
    let auth = Auth.auth();
    let currentUser = (auth.currentUser?.uid)! // (1)
    db.collection("UserData").document(currentUser).collection("Data").getDocuments { [self] (snapshot, error) in
      guard let snapshot = snapshot, error == nil else {
        return
      }
      print("Number of documents fb logic get user data: \(snapshot.documents.count ?? -1)")
      snapshot.documents.forEach { documentSnapshot in
        let documentData = documentSnapshot.data()
        // CONVERT TO userObject here (removed for simplicity)
        localUserData.append(userObject)
      }
      self.userData = localUserData
    }
  }
}

您可以通过使用.map() 来转换您的文档来进一步改进此代码。看到我的article about mapping Firestore documents to/from Swift中的这个code snippet that is part：

listenerRegistration = db.collection("programming-languages") 
  .addSnapshotListener { [weak self] (querySnapshot, error) in
    guard let documents = querySnapshot?.documents else {
      self?.errorMessage = "No documents in 'programming-languages' collection"
      return
    }
          
    self?.programmingLanguages = documents.compactMap { queryDocumentSnapshot in
      let result = Result { try queryDocumentSnapshot.data(as: ProgrammingLanguage.self) }
    ...