Firestore数据无法同步到@Published变量，跨视图调用为空

我通过Firestore拉取数据并存储到@Published var userJournals中，初始拉取时已确认数据能成功映射，但在另一个视图调用该变量时却为空，求排查问题原因。

视图1：JournalDashLogic 逻辑类 #

class JournalDashLogic: ObservableObject {
  @Published var userJournals = [UserJournalEntry]()
  @Published var userJournalIDs = [String]()

  func grabUserJournals(journalID: String) {
    // 获取当前用户
    guard let uid = FirebaseManager.shared.auth.currentUser?.uid else {
      return
    }
    FirebaseManager.shared.firestore
      .collection("users")
      .document(uid)
      .collection("userJournalEntrys")
      .document(journalID)
      .collection("items")
      .addSnapshotListener { (snapshot, err) in
        guard let documents = snapshot?.documents else {
          print("no documents present")
          return
        }
        // 映射为日志条目结构体
        self.userJournals = documents.map { (querySnapshot) -> UserJournalEntry in
          let data = querySnapshot.data()
          let dateCreated = data["dateCreated"] as? String ?? ""
          let dayOfWeek = data["dayOfWeek"] as? String ?? ""
          let mealCalories = data["mealCalories"] as? Int ?? 0
          let mealCarbs = data["mealCarbs"] as? Int ?? 0
          let mealFat = data["mealFat"] as? Int ?? 0
          let mealName = data["mealName"] as? String ?? ""
          let mealProtein = data["mealProtein"] as? Int ?? 0
          let MealServing = data["MealServing"] as? Int ?? 0
          let mealSaved = data["saved"] as? Bool ?? false
          let mealTiming = data["timeCreated"] as? String ?? ""

          let entry = UserJournalEntry(
            id: UUID().uuidString, mealName: mealName, mealFat: mealFat, mealCarbs: mealCarbs,
            mealProtein: mealProtein, mealCalories: mealCalories, MealServing: MealServing,
            mealSaved: mealSaved, mealTiming: mealTiming, dayOfWeek: dayOfWeek,
            totalCalories: "100", dateCreated: dateCreated)

          return entry
        }
      }
  }
}

视图2：触发数据拉取的代码 #

.onAppear {
  for id in jm.userJournalIDs {
    jm.grabUserJournals(journalID: id)
  }
}

视图2中弹出的Sheet #

.sheet(isPresented: $showAllJournals) {
  SavedJournalsList(savedJournalIDs: jm.userJournalIDs, savedJournals: jm.userJournals)
    .transition(transition)
}

视图3：SavedJournalsList 展示页 #

struct SavedJournalsList: View {
  @State var savedJournalIDs: [String]
  @State var savedJournals: [UserJournalEntry]

  var body: some View {
    VStack(alignment: .leading) {
      ForEach(savedJournals, id: \.self) { entry in
        HStack {
          Text(entry.dateCreated).bold()
          Text("Total Calories: 3200")
            .padding(.leading, 15)
        }
        .frame(maxWidth: .infinity)
        .multilineTextAlignment(.center)
        HStack {
          Text("200 Carbs")
            .foregroundColor(.gray)
          Text("250 Protein")
            .foregroundColor(.gray)
          Text("100 Fat")
            .foregroundColor(.gray)
        }
        .padding(.all, 5)
        .frame(maxWidth: .infinity)
      }
      .frame(width: 300, height: 100)
      .background(.white)
      .cornerRadius(15)
      .shadow(color: Color("LighterGray"), radius: 5, x: 0, y: 8)
    }
  }
}

排查关键点 #

1. 数据被覆盖：每次调用grabUserJournals都会直接替换userJournals数组，循环多个journalID时，最后一次请求会覆盖之前所有结果。如果最后一个请求无数据，数组就会为空。
2. 状态传递错误：SavedJournalsList用@State接收savedJournals，但@State是视图内部状态，传递的是值拷贝，无法响应userJournals的异步更新，导致sheet里的视图拿不到最新数据。
3. Sheet初始化时机问题：sheet可能在Firestore数据加载完成前就已初始化，此时传递的userJournals还是空数组，后续数据更新不会同步到sheet内的视图。
4. ForEach渲染异常：ForEach(savedJournals, id: \.self)要求UserJournalEntry遵循Hashable协议，如果没实现，会导致渲染失败，看起来像数组为空。

修复建议 #

• 修改数据存储逻辑：把self.userJournals = documents.map { ... }改成self.userJournals.append(contentsOf: documents.map { ... })，避免覆盖之前的数据；或者按journalID分组存储，防止数据丢失。
• 正确传递状态：让SavedJournalsList直接观察JournalDashLogic实例，用@ObservedObject替代值传递：

struct SavedJournalsList: View {
  @ObservedObject var journalLogic: JournalDashLogic

  var body: some View {
    VStack(alignment: .leading) {
      ForEach(journalLogic.userJournals, id: \.id) { entry in
        // 原有视图代码
      }
    }
  }
}

然后在sheet中传递实例：

.sheet(isPresented: $showAllJournals) {
  SavedJournalsList(journalLogic: jm)
    .transition(transition)
}

• 让模型遵循Identifiable：给UserJournalEntry添加Identifiable协议，避免ForEach用\.self带来的问题：

struct UserJournalEntry: Identifiable {
  let id: String
  // 其他属性
}

• 添加加载状态：在JournalDashLogic中加@Published var isLoading = false，请求开始时设为true，完成后设为false，视图中根据状态显示占位符，避免过早展示空视图。

内容的提问来源于stack exchange，提问作者Swink