如何正确地将这些数据写入JSON文件而不覆盖文件？

Question

我正在写一个JSON文件到文档目录，我想把它保存在一个文件中，以后再读。这个结构是这样的。

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

然后我像这样写到文档里

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)
         }
    }
}

这样我只能添加一次数据 我不知道该如何在JSON文件中添加另一个 "行"，这样我就可以读取这些数据，然后用我的结构来解码它们，以便用于 tableView 后来。做出来的JSON文件是这样的。

我有什么办法可以调用 createJSON 函数，而不会覆盖整个文件，我应该如何去组织这些，以便当我读取JSON时，我可以简单地解码并访问信息。

更新一下。

利用这个，我可以在JSON文件中添加更多的行。

   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"}

但当我试图解析这个时，它却出错了。

Code=3840 "Garbage at end."

我到底做错了什么？

Answer 1

在我看来，问题很明显。你正在向一个现有的字典追加另一个字典，但你应该创建一个字典数组，以便能够向它追加一个字典。

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
    }
}

---

如果你想手动追加文本到你的json字符串，你需要寻找到文件结束前的位置，在下一个json对象之前添加一个逗号，并在它之后添加一个封闭的括号。

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)
        }
    }
}

---

Playground testing:

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(symptom: "Anxiety", severity: "Mild", comment: ""，时间戳："1592356106.966: "1592356106.9662929"），__lldb_expr_532.SymptomD(symptom: "Depression", severity: "中度"，评论：""，时间戳：""。""，时间戳："1592356106.97886"，__lldb_expr_532.SymptomD(symptom: "抑郁症"，严重程度："中度"，注释：""，时间戳： "1592356106.978864")]

editupdate.如果你需要更新你的JSON中的一个 "行"，你需要让你的struc符合等价，读取你的集合，并找到它的索引。

如果你需要更新JSON中的一个 "行"，你需要让你的struc符合equatable，读取你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
    }
}