代码之家 › 专栏 › 技术社区 › Optimalist

NSCoding和Codable属性<=>JSON格式<=>(读/写)文件

codable nscoding serialization swift json

0

Optimalist · 技术社区 · 6 年前

我需要从JSON格式的文件读取/写入可编码(例如,日期)和NSCoding(例如,NSMutableAttributedString)的属性。在研究了如何使用Codable读取和写入文件、如何使用JSON格式读取和写入文件,以及如何在某些属性不符合Codable(但确实符合NSCoding)时将NSCoding与Codable结合起来之后,我将下面的代码混在一起,并在这个过程中感到困惑。

import Foundation

class Content: Codable {

    // Content
    var attrStr = NSMutableAttributedString(string: "")
    var date: Date?

    // Initializer for content
    init(attrStr: NSMutableAttributedString, date: Date) {
        self.attrStr = attrStr
        self.date = date
}

    // Need to explicitly define because NSMutableAttributedString isn't codable
    enum CodingKeys: String, CodingKey {

        case attrStr
        case date
    }

    // Need to explicitly define the decoder. . . .
    required init(from decoder: Decoder) throws {

        let container = try decoder.container(keyedBy: CodingKeys.self)

        date = try container.decode(Date.self, forKey: .date)

        let attrStrData = try container.decode(Data.self, forKey: .attrStr)
        attrStr = NSKeyedUnarchiver.unarchiveObject(with: attrStrData) as? NSMutableAttributedString ?? NSMutableAttributedString(string: "Error!")
    }

    // Need to explicitly define the encoder. . . .
    func encode(to encoder: Encoder) throws {

        var container = encoder.container(keyedBy: CodingKeys.self)

        try container.encode(date, forKey: .date)

        let attrStrData = NSKeyedArchiver.archivedData(withRootObject: attrStr)
        try container.encode(attrStrData, forKey: .attrStr)
    }

    static func getFileURL() -> URL {

        // Get the directory for the file
        let docsDir = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!
        // Get the full path and filename
        return docsDir.appendingPathComponent("contentArray").appendingPathExtension("cntnt")
    }

    static func saveToFile(content: [Content]) {

        // Get the file's URL
        let fileURL = getFileURL()

        do {
            // Encode the data
            let data = try JSONEncoder().encode(content)
            // Write to a/the file
            try data.write(to: fileURL)

        } catch {
            print("Could not encode or save to the file!")
        }
    }

    static func loadFromFile() -> [Content] {

        // Get the file's URL
        let fileURL = getFileURL()

        do {
            // Read from the file
            let data = try Data(contentsOf: fileURL)
            // Decode the data
            return try JSONDecoder().decode([Content].self, from: data)

        } catch {
            print("Could not decode or read from the file!")
            return []
        }
    }
}

1 回复 | 直到 6 年前

1

Fabian 6 年前

关于你的选择,我不知道怎么做。

我给了实施 Codable 对于 NSMutableAttributedString Source

class MutableAttributedStringContainer: Codable {
    let attributedString: NSMutableAttributedString

    init(attributedString: NSMutableAttributedString) {
        self.attributedString = attributedString
    }

    public required init(from decoder: Decoder) throws {
        let container = try decoder.singleValueContainer()
        let data = try container.decode(Data.self)

        let archiver = try NSKeyedUnarchiver(forReadingFrom: data)
        attributedString = NSMutableAttributedString(coder: archiver)!
    }

    public func encode(to encoder: Encoder) throws {
        let archiver = NSKeyedArchiver(requiringSecureCoding: true)
        attributedString.encode(with: archiver)

        var container = encoder.singleValueContainer()
        try container.encode(archiver.encodedData)
    }
}

下面是一个如何使用它的例子。

func testing() {
    let attributedString = NSMutableAttributedString(string: "Hello world!")
    let attributedStringContainer = MutableAttributedStringContainer(attributedString: attributedString)

    // Necessary because encoding into a singleValueContainer() creates a
    // JSON fragment instead of a JSON dictionary that `JSONEncoder` wants
    // create.
    struct Welcome: Codable {
        var attributedString: MutableAttributedStringContainer
    }
    let welcome = Welcome(attributedString: attributedStringContainer)

    let encoder = JSONEncoder()
    encoder.outputFormatting = .prettyPrinted
    let data = try! encoder.encode(welcome)
    print(String(bytes: data, encoding: .utf8) as Any)

    let decoder = JSONDecoder()
    let welcome2 = try! decoder.decode(Welcome.self, from: data)
    print("decoded to string:", welcome2.attributedString.attributedString.string)
}

可编码的 结构相互建立。如果所有底层结构都实现编译器可以自己创建编码和解码函数。如果没有,开发人员必须对它们进行编码并将它们放在 CodingKey ,同样用于解码。

编码键 . 也许读一本 Raywenderlich Tutorial 可编码的 为了更好地理解它。

应该有一个可识别的处理流,但我看不出这三种解码器/编码器是如何相互作用或相互替代的。

NSCoding 与合作 NSKeyedUnarchiver/NSKeyedArchiver 和回报 NSData

可编码的 与任何支持 可编码的 JSONEncoder/JSONDecoder ,它返回 Data 以人类可读的格式 JSON .utf8 .