数组 – 如何让NSCoder对Swift结构数组进行编码/解码？

我有一个必须符合NSCoding并且包含一组UInt64值的对象.如何使用NSCoder对其进行编码/解码？额外问题：如何最紧凑地编码？ (它必须进入保存的Game Center状态数据,其大小有限.)

理想情况下,我只想写一个Int,它是数组的大小n,然后写入n次64位的UInt64,并以类似方式读取它.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) {
        // ???
    }


}

这是一个将UInt64数组编码为的可能解决方案
一个字节数组.它的灵感来自 How to serialize C array with NSCoding?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) // [1,18446744073709551615]

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($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,UInt64.max])
let data = NSKeyedArchiver.archivedData(withRootObject: obj)

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