swift - 转换为 Swift 4，不明确的下标错误

Question

我是 swift 的新手，目前在突出显示的代码部分面临问题，错误是下标的使用不明确。我尝试了在 stackoverflow 上可以找到的其他解决方案，但无法解决。请帮助我了解错误及其解决方案。

do{
    guard let jsonData = data else {
       throw MyError.FoundNil("JSON data issue!")
    }

    guard let dictionaryData = try? JSONSerialization.jsonObject(with: jsonData, options: .mutableContainers) as! [String:AnyObject] else {
        throw MyError.SerializationError("Unable to serialize")
    }

    guard let city = dictionaryData["city"]!["name"]!,
          // Error on next three lines
          let data1 = dictionaryData["list"]![0]! as? [String: AnyObject],
          let data2 = dictionaryData["list"]![1]! as? [String: AnyObject],
          let data3 = dictionaryData["list"]![2]! as? [String: AnyObject],
          let t1 = data1["t"] as? [String: AnyObject],
          let t2 = data2["t"] as? [String: AnyObject],
          let t3 = data3["t"] as? [String: AnyObject],
          let wDay1 = data1["w"]![0]! as? [String:AnyObject],
          let wDay2 = data2["w"]![0]! as? [String:AnyObject],
          let wDay3 = data3["w"]![0]! as? [String:AnyObject]
    else {
        throw MyError.DataPopulateError("Mismatch in assigning values from dictionary")
    }

Answer 1

首先，不要使用AnyObject。将您的字典定义为 [String: Any]。

接下来，问题是一旦您执行了类似dictionaryData["some key"] 的操作，您现在就有了一个Any。需要进行转换才能进一步处理它。错误是由于尝试在 Any 上使用数组索引访问。

最后，您误用了 ! 运算符。 guard let 的全部意义在于安全地解包和安全地转换一个值。您使用 ! 打败了整点，如果数据不是您的代码假定的数据，这将使您的应用程序崩溃。

将第 2 个守卫更新为:

guard let dictionaryData = try? JSONSerialization.jsonObject(with: jsonData, options: []) as! [String:Any] else {
    throw MyError.SerializationError("Unable to serialize")
}

然后重写你的大guard如下:

guard let city = (dictionaryData["city"] as? [String:Any])?["name"] as? String,
    let list = dictionaryData["list"] as? [[String:Any]], list.count >= 3,
    let t1 = list[0]["t"] as? [String:Any],
    let t2 = list[1]["t"] as? [String:Any],
    let t3 = list[2]["t"] as? [String:Any],
    let wDay1 = (list[0]["w"] as? [[String:Any]])?.first,
    let wDay2 = (list[1]["w"] as? [[String:Any]])?.first,
    let wDay3 = (list[2]["w"] as? [[String:Any]])?.first
else {
    throw MyError.DataPopulateError("Mismatch in assigning values from dictionary")
}