如何在不覆盖文件的情况下正确将此数据写入 JSON 文件？

Question

我正在将 JSON 文件写入文档目录，我想将其保存在一个文件中，稍后再阅读。结构如下所示：

struct SymptomD:Codable
{
var symptom:String
var severity:String
var comment:String
var timestamp:String
}

然后我像这样写文件：

var completeData = SymptomD(symptom: "", severity: "", comment: "", timestamp: "")
func writeTrackedSymptomValues(symptom: String, comment: String, time: String, timestamp: String) {
    completeData.symptom = symptom
    completeData.severity = self.severity
    completeData.comment = comment
    completeData.timestamp = timestamp

    createJSON()
}

    var logFile: URL? {
        guard let documentsDirectory = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first else { return nil }
        let fileName = "symptom_data.json"
        return documentsDirectory.appendingPathComponent(fileName)
    }

func createJSON() {
    guard let logFile = logFile else {
        return
    }

    let jsonData = try! JSONEncoder().encode(completeData)
    let jsonString = String(data: jsonData, encoding: .utf8)!
    print(jsonString)

    if FileManager.default.fileExists(atPath: logFile.path) {
        if let fileHandle = try? FileHandle(forWritingTo: logFile) {
            fileHandle.seekToEndOfFile()
            fileHandle.write(completeData) //This does not work, I am not sure how to add data without overwriting the previous file.
            fileHandle.closeFile()
        }
    } else {

         do {

             try JSONEncoder().encode(completeData)
                 .write(to: logFile)
         } catch {
             print(error)
         }
    }
}

有了这个我只能添加一次数据，我不确定我应该如何将另一个“行”基本上添加到 JSON 文件中，以便我可以读取这些数据并使用我的结构对其进行解码以用于 @ 987654325@ 稍后。生成的 JSON 文件如下所示：

有什么方法可以在不覆盖整个文件的情况下再次调用createJSON 函数，以及我应该如何组织它以便在读取 JSON 时可以简单地对其进行解码并访问信息。

更新：

使用它我可以向 JSON 添加更多行，

   let jsonData = try! JSONEncoder().encode(completeData)
    let jsonString = String(data: jsonData, encoding: .utf8)!
    print(jsonString)

    if FileManager.default.fileExists(atPath: logFile.path) {
        if let fileHandle = try? FileHandle(forWritingTo: logFile) {
            fileHandle.seekToEndOfFile()
            fileHandle.write(jsonData)
            fileHandle.closeFile()
        }

给我这个：

   {"timestamp":"1592341465","comment":"","severity":"Mild","symptom":"Anxiety"}{"timestamp":"1592342433","comment":"","severity":"Moderate","symptom":"Anxiety"}{"timestamp":"1592342458","comment":"","severity":"Mild","symptom":"Anxiety"}{"timestamp":"1592343853","comment":"","severity":"Mild","symptom":"Anxiety"}{"timestamp":"1592329440","comment":"","severity":"Mild","symptom":"Fatigue"}{"timestamp":"1592344328","comment":"","severity":"Mild","symptom":"Mood Swings"}{"timestamp":"1592257920","comment":"test","severity":"Mild","symptom":"Anxiety"}

但是当试图解析这个时，它会崩溃并出现错误：

Code=3840 "Garbage at end."

我做错了什么？

Answer 1

这个问题对我来说很清楚。您正在将另一个字典附加到现有字典，但您应该创建一个字典数组以便能够将字典附加到它。

struct SymptomD: Codable {
    var symptom, severity, comment, timestamp: String
    init(symptom: String = "", severity: String = "", comment: String = "", timestamp: String = "") {
        self.symptom = symptom
        self.severity = severity
        self.comment = comment
        self.timestamp = timestamp
    }
}

---

如果您想手动将文本附加到您的 json 字符串，您需要查找文件末尾之前的位置，在下一个 json 对象之前添加一个逗号并在其后添加一个右括号：

extension SymptomD {
    func write(to url: URL) throws {
        if FileManager.default.fileExists(atPath: url.path) {
            let fileHandle = try FileHandle(forWritingTo: url)
            try fileHandle.seek(toOffset: fileHandle.seekToEndOfFile()-1)
            let data = try JSONEncoder().encode(self)
            fileHandle.write(Data(",".utf8) + data + Data("]".utf8))
            fileHandle.closeFile()
        } else {
            try JSONEncoder().encode([self]).write(to: url)
        }
    }
}

---

游乐场测试：

var logFile: URL? {
    FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first?.appendingPathComponent("symptom_data.json")
}

var symptomD = SymptomD()
symptomD.symptom = "Anxiety"
symptomD.severity = "Mild"
symptomD.timestamp = .init(Date().timeIntervalSince1970)
do {
    if let logFile = logFile {
        try symptomD.write(to: logFile)
    }
} catch {
    print(error)
}

var symptomD2 = SymptomD()
symptomD2.symptom = "Depression"
symptomD2.severity = "Moderate"
symptomD2.timestamp = .init(Date().timeIntervalSince1970)
do {
    if let logFile = logFile {
        try symptomD2.write(to: logFile)
    }
} catch {
    print(error)
}

do {
    if let logFile = logFile {
        let symptoms = try JSONDecoder().decode([SymptomD].self, from: .init(contentsOf: logFile))
        print(symptoms)
    }
} catch {
    print(error)
}

这将打印：

[__lldb_expr_532.SymptomD（症状：“焦虑”，严重性：“轻度”， 评论：“”，时间戳：“1592356106.9662929”）， __lldb_expr_532.SymptomD（症状：“抑郁”，严重性：“中度”，评论：“”，时间戳：“1592356106.978864”）]

编辑/更新：

如果您需要更新 JSON 的单个“行”，则需要使您的 struc 符合 equatable，读取您的集合并找到它的索引：

extension SymptomD: Equatable {
    static func ==(lhs: SymptomD, rhs: SymptomD) {
        (lhs.symptom, lhs.severity, lhs.comment ,lhs.timestamp) ==
        (rhs.symptom, rhs.severity, rhs.comment ,rhs.timestamp)
    }
    @discardableResult
    mutating func updateAndWrite(symptom: String? = nil, severity: String? = nil, comment: String? = nil, timestamp: String? = nil, at url: URL) throws -> [SymptomD]? {
        var symptoms = try JSONDecoder().decode([SymptomD].self, from: .init(contentsOf: url))
        if let index = symptoms.firstIndex(of: self) {
            self.symptom = symptom ?? self.symptom
            self.severity = severity ?? self.severity
            self.comment = comment ?? self.comment
            self.timestamp = timestamp ?? self.timestamp
            symptoms[index] = self
            try JSONEncoder().encode(symptoms).write(to: url, options: .atomic)
            return symptoms
        }
        return nil
    }
}