我怎样才能让 NSCoder 到 encode/decode 一个 Swift 结构数组？

Question

我有一个对象必须符合 NSCoding 并且包含一个 UInt64 值数组。我怎么能用 NSCoder encode/decode 呢？奖励问题：我怎样才能最紧凑地编码它？（它必须进入已保存的 Game Center 状态数据，其大小有限。）

理想情况下，我只想写一个Int，也就是数组的大小n，然后写n乘以一个UInt64的64位, 并以类似的方式阅读。我可以这样做吗？

coder.encodeObject(values, forKey: "v") 无效。

class MyObject: NSCoding {

    private var values: [UInt64]

    // …

    // MARK: - NSCoding

    required init(coder decoder: NSCoder) {
        // ???
    }

    func encodeWithCoder(coder: NSCoder) {
        // ???
    }


}

Answer 1

这是一个可能的解决方案，将 UInt64 数组编码为字节数组。它的灵感来自 .

的答案

class MyObject: NSObject, NSCoding {

    var values: [UInt64] = []

    init(values : [UInt64]) {
        self.values = values
    }

    // MARK: - NSCoding
    required init(coder decoder: NSCoder) {
        super.init()
        var count = 0
        // decodeBytesForKey() returns an UnsafePointer<UInt8>, pointing to immutable data.
        let ptr = decoder.decodeBytesForKey("values", returnedLength: &count)
        // If we convert it to a buffer pointer of the appropriate type and count ...
        let buf = UnsafeBufferPointer<UInt64>(start: UnsafePointer(ptr), count: count/sizeof(UInt64))
        // ... then the Array creation becomes easy.
        values = Array(buf)
    }

    func encodeWithCoder(coder: NSCoder) {
        // This encodes both the number of bytes and the data itself.
        coder.encodeBytes(UnsafePointer(values), length: values.count * sizeof(UInt64), forKey: "values")
    }
}

测试：

let obj = MyObject(values: [1, 2, 3, UInt64.max])
let data = NSKeyedArchiver.archivedDataWithRootObject(obj)

let dec = NSKeyedUnarchiver.unarchiveObjectWithData(data) as! MyObject
print(dec.values) // [1, 2, 3, 18446744073709551615]

更新 Swift 3 (Xcode 8):

class MyObject: NSObject, NSCoding {

    var values: [UInt64] = []

    init(values : [UInt64]) {
        self.values = values
    }

    // MARK: - NSCoding
    required init(coder decoder: NSCoder) {
        super.init()
        var count = 0
        // decodeBytesForKey() returns an UnsafePointer<UInt8>?, pointing to immutable data.
        if let ptr = decoder.decodeBytes(forKey: "values", returnedLength: &count) {
            // If we convert it to a buffer pointer of the appropriate type and count ...
            let numValues = count / MemoryLayout<UInt64>.stride
            ptr.withMemoryRebound(to: UInt64.self, capacity: numValues) {
                let buf = UnsafeBufferPointer<UInt64>(start: UnsafePointer([=12=]), count: numValues)
                // ... then the Array creation becomes easy.
                values = Array(buf)
            }
        }
    }

    public func encode(with coder: NSCoder) {
        // This encodes both the number of bytes and the data itself.
        let numBytes = values.count * MemoryLayout<UInt64>.stride
        values.withUnsafeBufferPointer {
            [=12=].baseAddress!.withMemoryRebound(to: UInt8.self, capacity: numBytes) {
                coder.encodeBytes([=12=], length: numBytes, forKey: "values")
            }
        }
    }
}


let obj = MyObject(values: [1, 2, 3, UInt64.max])
let data = NSKeyedArchiver.archivedData(withRootObject: obj)

let dec = NSKeyedUnarchiver.unarchiveObject(with: data) as! MyObject
print(dec.values) // [1, 2, 3, 18446744073709551615]

我怎样才能让 NSCoder 到 encode/decode 一个 Swift 结构数组？

How can I get an NSCoder to encode/decode a Swift array of structs?

arrays

serialization

nscoding

swift