Swift MultiDatePicker加载Firebase日期后无法识别已选日期

从Firebase加载日期到MultiDatePicker后，点击已选中的日期无法将其从selectedDates集合中移除，反而会重复添加。无Firebase数据时，日期的选择/取消功能正常，仅在加载数据后出现该问题。

相关代码 #

视图代码 #

VStack {
    MultiDatePicker("Select dates", selection: $selectedDates)
        .padding()
        .onChange(of: selectedDates) { oldValue, newValue in
            saveDates(dates: selectedDates)
         }
    List(savedDates, id: \.self) { date in
        Text("\(date, formatter: dateFormatter)")
    }
    .listStyle(.plain)
}
.onAppear {
    loadSavedDates()
}

状态变量 #

@State var selectedDates: Set<DateComponents> = []

Firebase加载日期代码 #

func loadSavedDates() {
        let db = Firestore.firestore()
        let uid = try! AuthenticationManager.shared.getAuthenticatedUser().uid
        print("User ID: \(uid)")
        print(widget.id.uuidString)
        
        db.collection("spaces")
            .document(spaceId)
            .collection("dates")
            .document(widget.id.uuidString)//widget.id.uuidString
            .getDocument {document, error in
                if let document = document {
                    if let dateStrings = document.data()?[uid] as? [String] {
                        let dateFormatter = DateFormatter()
                        dateFormatter.dateStyle = .medium
                        self.savedDates = dateStrings.compactMap { dateFormatter.date(from: $0) }.sorted()
                        let calendar = Calendar.current
                        self.selectedDates = Set(self.savedDates.map { calendar.dateComponents([.year, .month, .day], from: $0) })
                        for component in selectedDates {
                            print(component.isValidDate)
                        }
                    }
                } else {
                    print("Document does not exist")
                }
            }
}

问题原因与解决方案 #

核心原因 #

DateComponents的相等性判断依赖于所有包含的组件。你从Firebase加载转换的DateComponents，可能隐式包含了时区、时分秒等未显式指定的组件，而MultiDatePicker内部生成的DateComponents仅包含.year、.month、.day，导致集合认为这是两个不同元素，点击时无法匹配移除，反而重复添加。

解决方案 #

1. 严格指定DateComponents的组件范围
   转换日期时，确保只提取.year、.month、.day三个组件，避免多余组件干扰。同时给DateFormatter显式设置时区，避免解析时的时区差异。

   修改后的加载代码：

   func loadSavedDates() {
       let db = Firestore.firestore()
       guard let uid = try? AuthenticationManager.shared.getAuthenticatedUser().uid else { return }
       
       db.collection("spaces")
           .document(spaceId)
           .collection("dates")
           .document(widget.id.uuidString)
           .getDocument { document, error in
               guard let document = document, document.exists else {
                   print("Document does not exist")
                   return
               }
               
               guard let dateStrings = document.data()?[uid] as? [String] else { return }
               
               let dateFormatter = DateFormatter()
               dateFormatter.dateStyle = .medium
               // 显式设置时区，避免解析时的时区偏移
               dateFormatter.timeZone = TimeZone(identifier: "UTC")
               
               self.savedDates = dateStrings.compactMap { dateFormatter.date(from: $0) }.sorted()
               
               let calendar = Calendar.current
               // 严格只提取年、月、日组件
               self.selectedDates = Set(self.savedDates.map { 
                   calendar.dateComponents([.year, .month, .day], from: $0) 
               })
           }
   }
   

2. 优化onChange回调
   直接使用newValue参数，避免读取状态变量的延迟问题：

   .onChange(of: selectedDates) { oldValue, newValue in
       saveDates(dates: newValue)
   }
   

3. 可选：自定义DateComponents的相等性判断
   如果上述方法仍无效，可以扩展DateComponents，手动实现基于年/月/日的相等性和哈希值：

   extension DateComponents: Hashable {
       public static func == (lhs: DateComponents, rhs: DateComponents) -> Bool {
           return lhs.year == rhs.year && lhs.month == rhs.month && lhs.day == rhs.day
       }
       
       public func hash(into hasher: inout Hasher) {
           hasher.combine(year)
           hasher.combine(month)
           hasher.combine(day)
       }
   }
   

内容的提问来源于stack exchange，提问作者Joshua Shen