无法使用“String”类型的索引为“[CustomObject]”类型的值下标

Question

我们将 json 数据放入自定义对象中：

 "sentMoney": [
                {
                    "amount": 3840.83,
                    "currency": "MXN",
                    "isMajor": false
                },
                {
                    "amount": 200,
                    "currency": "USD",
                    "isMajor": true
                }
        ]

public final class SentMoney: NSCoding {
  public var currency: String?
  public var isMajor: Bool? = false
  public var amount: Double?
}

然后在变量中引用自定义对象：

 public var sentMoney: [SentMoney]?

现在我们要做的只是获得第一个金额 (3840.83)。

我尝试过这样做，但出现错误：

 let amountsOnlyArray = self.postTransferSuccess?.sentMoney.map({ $0["amount"] })//Error -Cannot subscript a value of type '[SentMoney]' with an index of type 'String' 
 let firstAmountOnly = self.postTransferSuccess?.sentMoney![0]["amount"]//Error -Type 'BSentMoney' has no subscript members

有没有更好的方法来获得第一笔金额？

Answer 1

当您将变量 sentMoney 显式声明为 [SentMoney] 时，您可以在映射数组或索引元素时直接使用对象的属性，如下所示。

let amountsOnlyArray = self.postTransferSuccess?.sentMoney.map({ $0.amount })

或

let firstAmountOnly = self.postTransferSuccess?.sentMoney![0].amount

Answer 2

看起来您正在将 JSON 解析为一个想要访问该对象的属性的对象。您应该使用点符号来访问它，例如$0.amount

let amountsOnlyArray = self.postTransferSuccess?.sentMoney.map({ $0.amount })
let firstAmountOnly = self.postTransferSuccess?.sentMoney![0].amount

编辑

这里有一个更全面的例子：

class SentMoney {
    public var currency: String?
    public var isMajor: Bool? = false
    public var amount: Double?
}

let one = SentMoney()
one.amount = 1.2

let two = SentMoney()
two.amount = 3.4

let sentMoney = [one, two]

let amountsOnlyArray = sentMoney.map({ $0.amount })

amountsOnlyArray // [{some 1.2}, {some 3.4}]

sentMoney.first?.amount // 1.2