大家周日快乐。我在解码数据时遇到了一个问题。当我将字典字符串序列化为一个对象时，我似乎无法解码数据。我试图从firebase中获取匹配项，这在获取用户配置文件时有效，但在获取匹配项时无效。

func fetchMatches(onCompletion: @escaping (Result<[MatchModel], DomainError>) -> ()){
        db.collection("matches").whereField("usersMatched", arrayContains: userId!).getDocuments(completion: {doc, err in
            guard let documentSnapshot = doc, err == nil else{
                onCompletion(.failure(.downloadError))
                return
            }
            var matchList: [MatchModel] = []
            var count = 0
            let maxCount = documentSnapshot.documents.count
            var hasFailed = false
            for document in documentSnapshot.documents{
                if hasFailed{ break }

                let decoder = JSONDecoder()
                var dict = document.data()

                for (key, value) in dict {

                if let value = value as? Timestamp {

                    let formatter = DateFormatter()
                    let newValue = value.dateValue()
                    formatter.dateStyle = .short
                    formatter.timeStyle = .none
                    dict[key] = formatter.string(from: newValue)
                   }
                 }

到这里为止，我知道一切都很顺利。字典包含-

Dictionary
["timestamp": "10/22/22", "usersMatched": <__NSArrayM 0x600002c61680>(
6euZHDmI7PMDcCmft5MfxUW27jI3,
tbcB0ay0YEgZcY9UsZ00WjZ9h893
)
]

下面的数据打印出105个字节，因此根据这些信息，我知道它不是空的，并且JSONSerialization完成了将dict转换为对象的工作。

if let data = try? JSONSerialization.data(withJSONObject: dict, options:[]){   

do{       
 let match = try? decoder.decode(FirestoreMatch.self, from: data)

let matchId : String = match!.usersMatched.filter{$0 != self.userId!}.first!

... }
catch{ 
print(error)

错误返回：

typeMismatch(Swift.Double, Swift.DecodingError.Context(codingPath: [CodingKeys(stringValue: "timestamp", intValue: nil)], debugDescription: "Expected to decode Double but found a string/data instead.", underlyingError: nil))

这是我的FirestoreMatch结构体

struct FirestoreMatch: Codable{
    let usersMatched: [String]
    let timestamp: Date
}

我的结构体需要更多的信息吗？我不知道为什么match返回nil