如何在 Swift 中将键值对添加到类型为 [String:AnyObject] 的字典中？

Question

我已将 JSON 文件的内容存储在 [[String:AnyObject]] 类型的字典数组中。我想为 [String:AnyObject] 字典中的每个项目添加一个新的键值对。我不断收到错误消息：无法分配给“AnyObject？！”类型的不可变表达式 有没有办法解决这个问题？

主题声明如下：

    var subjects = [[String:AnyObject]]()

编辑：很抱歉没有发布代码。所以，这是 [[String:AnyObject]] 数组的元素之一

   { "subjects" : {
        "humanities" : [
            {"sno" : "TH5", "code" : 205, "name" : "Mathematics III", "credits" : 4}
        ],
        "applied" : [
            {"sno" : "TH3", "code" : 203, "name" : "Power Apparatus", "credits" : 4},
            {"sno" : "TH4", "code" : 204, "name" : "Electrical Measurements", "credits" : 4}
        ],
        "core" : [
            {"sno" : "TH1", "code" : 201, "name" : "Electronics I", "credits" : 4},
            {"sno" : "TH2", "code" : 202, "name" : "Circuits and Systems", "credits" : 4}
        ],
        "theory" : [
            {"sno" : "TH1", "code" : 201, "name" : "Electronics I", "credits" : 4, "category" : "C"},
            {"sno" : "TH2", "code" : 202, "name" : "Circuits and Systems", "credits" : 4, "category" : "C"},
            {"sno" : "TH3", "code" : 203, "name" : "Power Apparatus", "credits" : 4, "category" : "A"},
            {"sno" : "TH4", "code" : 204, "name" : "Electrical Measurements", "credits" : 4, "category" : "A"},
            {"sno" : "TH5", "code" : 205, "name" : "Mathematics III", "credits" : 4, "category" : "H"}
        ],
        "practical" : [
            {"sno" : "PR1", "code" : 206, "name" : "Electronics I", "credits" : 2},
            {"sno" : "PR2", "code" : 207, "name" : "Power Apparatus", "credits" : 2},
            {"sno" : "PR3", "code" : 208, "name" : "Electrical Measurements", "credits" : 2},
            {"sno" : "PR4", "code" : 209, "name" : "Machine Drawing", "credits" : 3},
            {"sno" : "VS1", "code" : 210, "name" : "Programming I", "credits" : 1}
        ]
    },
    "totalCredits" : 30,
    "semester" : 3
    }

八个这样的字典存储在“主题”中。我想在“humanities”、“applied”等每个元素中添加另一个键值对“marks”：0。 这是我正在使用的代码，例如“人文”

    for i in 0..<self.subjects.count
        {
            for j in 0..<self.subjects[i]["humanities"]!.count
            {
                self.subjects[i]["humanities"]![j]["marks"] = 0
            }
        }

这就是我得到错误的地方。

编辑 2：添加了附加声明

Answer 1

主要问题是您不会像在数组中那样为字典分配值。

如果您像这样访问字典中的值：

var dictionaryValues = dictionary.values

然后尝试更改该数组 'dictionaryValues' 中的值，您正在尝试错误地更新字典。

更改字典中条目的方法是根据关联的键分配值。

所以我知道要更改的值的键，您可以像这样分配新值：

let key = "keyForValueYouWishToChange"
let newValue: AnyObject = 1

for (index, dictionary) in arrayOfDictionaries.enumerate() {
    var mutableDictionary = dictionary
    mutableDictionary[key] = newValue //this is how you assign to dictionaries
    arrayOfDictionaries[index] = mutableDictionary
 }

另外，将您的字典更改为 var 而不是 let，以便它是可变的

Answer 2

很难理解你真正想要做什么。您不会在内存中保留[String : [String : [[String : Any]]]] 之类的结构并将内容修改为该结构，这很可能是您收到此错误的原因。你必须从这个结构中“提取”并使用它。如果你想把它重新转换成 JSON，你必须再次序列化它，反之亦然。 首先，我将向您展示如何从 JSON 中获取单个主题：

// Mockup String
let jsonString = "{ \"subjects\" : { \"humanities\" : [ {\"sno\" : \"TH5\", \"code\" : 205, \"name\" :     \"Mathematics III\", \"credits\" : 4} ], \"applied\" : [ {\"sno\" : \"TH3\", \"code\" : 203, \"name\" : \"Power     Apparatus\", \"credits\" : 4}, {\"sno\" : \"TH4\", \"code\" : 204, \"name\" : \"Electrical Measurements\",     \"credits\" : 4} ], \"core\" : [ {\"sno\" : \"TH1\", \"code\" : 201, \"name\" : \"Electronics I\", \"credits\" :     4}, {\"sno\" : \"TH2\", \"code\" : 202, \"name\" : \"Circuits and Systems\", \"credits\" : 4} ], \"theory\" : [     {\"sno\" : \"TH1\", \"code\" : 201, \"name\" : \"Electronics I\", \"credits\" : 4, \"category\" : \"C\"},     {\"sno\" : \"TH2\", \"code\" : 202, \"name\" : \"Circuits and Systems\", \"credits\" : 4, \"category\" : \"C\"},     {\"sno\" : \"TH3\", \"code\" : 203, \"name\" : \"Power Apparatus\", \"credits\" : 4, \"category\" : \"A\"},     {\"sno\" : \"TH4\", \"code\" : 204, \"name\" : \"Electrical Measurements\", \"credits\" : 4, \"category\" :     \"A\"}, {\"sno\" : \"TH5\", \"code\" : 205, \"name\" : \"Mathematics III\", \"credits\" : 4, \"category\" :     \"H\"} ], \"practical\" : [ {\"sno\" : \"PR1\", \"code\" : 206, \"name\" : \"Electronics I\", \"credits\" : 2},     {\"sno\" : \"PR2\", \"code\" : 207, \"name\" : \"Power Apparatus\", \"credits\" : 2}, {\"sno\" : \"PR3\",     \"code\" : 208, \"name\" : \"Electrical Measurements\", \"credits\" : 2}, {\"sno\" : \"PR4\", \"code\" : 209,     \"name\" : \"Machine Drawing\", \"credits\" : 3}, {\"sno\" : \"VS1\", \"code\" : 210, \"name\" : \"Programming     I\", \"credits\" : 1} ] }, \"totalCredits\" : 30, \"semester\" : 3 }"

// use a function to directly retrieve a single subject
func getSubject(subject: String) -> [String: Any]? {

    // use some guards to keep the nesting depth minimal

    // read the json string
    let data = jsonString.data(using: .utf8)
    guard data != nil else {
        return nil
    }

    // try to parse the json
    let parsedJson = try? JSONSerialization.jsonObject(with: data!) as? [String: Any]
    guard parsedJson != nil else {
        return nil
    }

    // read the subjects
    if let jsonDictionary = parsedJson! {
        let subjects = jsonDictionary["subjects"] as? [String: Any]
        guard subjects != nil else {
            return nil
        }

        // get a single subject and interpret it as array
        if let singleSubject = subjects![subject] as? [Any] {
            // check if it contains elements
            if singleSubject.count > 0 {
                // return the first (and only) entry as dictionary
                return singleSubject[0] as? [String: Any]
            }
        }
    }

    return nil
}

if var humanities = getSubject(subject: "humanities") {

    // add a new entry
    humanities["marks"] = 0

    // print out all entries to check
    for (key, value) in humanities {
        print("\(key): \(value)")
    }
}

打印：

name: Mathematics III
marks: 0
sno: TH5
code: 205
credits: 4