swift - 如何访问结构中的字典

Question

我有一个结构，结构内部有一个字典，我想访问结构内部字典的内容。

这是我的结构:

struct TransactionsObject: Codable {
    let UserInitiatedTransactions: [UserEdTransaction]?
    let UserReceivedTransactions: [UserEdTransaction]?

    enum CodingKeys: String, CodingKey {
        case UserInitiatedTransactions = "UserInitiatedTransactions"
        case UserReceivedTransactions = "UserReceivedTransactions"
    }
}

struct UserEdTransaction: Codable {
    let transactionCode: Int?
    let transactionDate: String?
    let transactionType: String?
    let transactionTime: String?
    let transactionAmount: String?
    let transactionTo: String?
    let transactionFrom: String?

    enum CodingKeys: String, CodingKey {
        case transactionCode = "transactionCode"
        case transactionDate = "transactionDate"
        case transactionType = "transactionType"
        case transactionTime = "transactionTime"
        case transactionAmount = "transactionAmount"
        case transactionTo = "transactionTo"
        case transactionFrom = "transactionFrom"
    }
}

我想访问这个transactionCode。我已经对 TransactionsObject.UserInitiatedTransactions.transactionCode 进行了尝试，但出现以下错误:

Value of type '[UserEdTransaction]?' has no member 'transactionCode'

Answer 1

首先的问题应该是如何访问结构中的数组 😉

其次，仅当结构成员和键与例如lowerCamelCase 变量名称不匹配时才使用CodingKeys。

第三点仅将结构的成员声明为可选的，其键等价物可能会丢失

struct TransactionsObject: Codable {
    let userInitiatedTransactions: [UserEdTransaction]
    let userReceivedTransactions: [UserEdTransaction]

    enum CodingKeys: String, CodingKey {
        case userInitiatedTransactions = "UserInitiatedTransactions"
        case userReceivedTransactions = "UserReceivedTransactions"
    }
}

struct UserEdTransaction: Codable { // no CodingKeys !!
    let transactionCode: Int
    let transactionDate: String
    let transactionType: String
    let transactionTime: String
    let transactionAmount: String
    let transactionTo: String
    let transactionFrom: String
}

---

错误发生是因为userInitiatedTransactions 是一个数组。您需要索引订阅

print(transactionsObject.userInitiatedTransactions[0]) // can crash if the array is empty

或重复循环

for transaction in transactionsObject.userInitiatedTransactions {
    print(transaction.transactionCode)
}