如何在 Swift 中將鍵值對添加到 [String:AnyObject] 類型的字典中？

Question

我已將 JSON 文件的內容存儲在 [[String:AnyObject]] 類型的字典數組中。 我想為 [String:AnyObject] 字典中的每個項目添加一個新的鍵值對。 我不斷收到錯誤消息：無法分配給類型為“AnyObject?!”的不可變表達式有沒有辦法解決？

已聲明主題如下：

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

編輯：抱歉沒有發布代碼。所以，這是 [[String:AnyObject]] 數組的元素之一

   { "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
    }

八本這樣的詞典存儲在“主題”中。 我想向“人文”、“應用”等中的每個元素添加另一個鍵值對“標記”：0。 這是我使用的代碼，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
            }
        }

這就是我得到錯誤的地方。

編輯 2：添加了附加聲明

Answer 1

主要問題是您沒有像在數組中那樣為字典賦值。

如果您像這樣訪問字典中的值：

var dictionaryValues = dictionary.values

然后嘗試更改該數組 'dictionaryValues' 中的值，您試圖錯誤地更新字典。

更改字典中條目的方法是根據其關聯的鍵分配值。

所以我知道你想要更改的值的鍵，你可以像這樣分配新值：

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
 }

此外，將您的字典更改為 var 而不是 let，因此它是可變的

Answer 2

很難理解你真正想要做什么。 您不會在內存中保留像[String : [String : [[String : Any]]]]的結構並將內容修改為該結構，這很可能是您收到此錯誤的原因。 你必須從這個結構中“提取”出來並使用它。 如果您想將其恢復為 JSON，則必須再次將其序列化，反之亦然。 首先，我將向您展示如何從 JSON 中獲取單個主題：

// 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)")
    }
}

印刷：

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