从字典数组映射到 Swift 中的数字数组

Posted 2023-03-17

【中文标题】从字典数组映射到 Swift 中的数字数组

【英文标题】：Mapping from array of dictionaries to array of numbers in Swift

【发布时间】：2018-12-24 23:44:34

【问题描述】：

这是一个函数，它应该将包含 Dictionary<String, Any> 的订单 NSArray 的键值对数组转换为每个订单的 ID 数组 ([NSNumber])。

但是，我仍然遇到类型转换的问题，错误：

类型 'Any' 没有下标成员

如何在 Swift 中干净利落地执行映射？

@objc static func ordersLoaded(notification:Notification) -> [NSNumber]    

    // Function receives a Notification object from Objective C     
    let userInfo:Dictionary = notification.userInfo as! Dictionary<String, Any>

    // orders is an array of key-value pairs for each order Dictionary<String,Any>
    let ordersWithKeyValuePairs:NSArray = userInfo["orders"] as! NSArray // Here a typed array of Dictionaries would be preferred

    // it needs to be simplified to an array of IDs for each order (NSNumber)
    // orderID is one of the keys
    let orderIDs:[NSNumber];
    orderIDs = ordersWithKeyValuePairs.flatMap($0["orderID"] as? NSNumber) // Line with the error
    /*
    orderIDs = ordersWithKeyValuePairs.map(
        (key,value) in
        if key==["orderID"] 
            return value
         else 
            return nil
        
    ) as! [NSNumber]
    */

    return orderIDs

【问题讨论】：

NSArray 的定义类似于[Any]，这就是您遇到问题的原因。不要在 Swift 中使用 NS 类，除非你真的必须这样做。在这种情况下，转换为预期的类型，可能是：[AnyHashable: Any]

在执行orderIDs = ordersWithKeyValuePairs.flatMap($0["orderID"] as? NSNumber)时仍然收到错误Type 'AnyHashable' has no subscript members

【参考方案1】：

你可以试试这个

if let ordersWithKeyValuePairs = userInfo["orders"] as? [[String:Any]] 

   let result = ordersWithKeyValuePairs.compactMap$0["orderID"] as? Int 

【参考方案2】：

这是有效的，将ordersWithKeyValuePairs 转换为[Dictionary<String, Any>] 解决了我的问题：

@objc static func ordersLoaded(notification:Notification) -> [NSNumber]    

    // Function receives a Notification object from Objective C     
    let userInfo:Dictionary = notification.userInfo as! Dictionary<String, Any>

    // orders is an array of key-value pairs for each order Dictionary<String,Any>
    let ordersWithKeyValuePairs:[Dictionary<String, Any>] = userInfo["orders"] as! [Dictionary<String, Any>]
    // it needs to be simplified to an array of IDs for each order (NSNumber)
    // orderID is one of the keys
    let orderIDs:[NSNumber];
    orderIDs = ordersWithKeyValuePairs.flatMap($0["orderID"] as? NSNumber) // Line with the error

    return orderIDs