如何获得NSCoder来编码/解码Swift结构数组？

Question

我有一个必须符合NSCoding且包含UInt64值数组的对象。我怎么能用/对其进行编码/解码NSCoder？额外的问题：如何编码最紧凑？（它必须进入保存的Game
Center状态数据，其大小是有限的。）

理想情况下，我只想写一个等于数组Int大小n的an ，然后写n乘a的64位乘以UInt64类似的方式读取它。我可以这样做吗？

coder.encodeObject(values, forKey: "v") 不起作用。

class MyObject: NSCoding {

    private var values: [UInt64]

    // …

    // MARK: - NSCoding

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

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


}

Answer 1

这是将UInt64数组编码为字节数组的可能解决方案。它的灵感来自于如何使用NSCoding序列化C数组？。

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]

Swift 3（Xcode 8）更新：

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($0), 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 {
            $0.baseAddress!.withMemoryRebound(to: UInt8.self, capacity: numBytes) {
                coder.encodeBytes($0, 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]