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。)
NSCoding
UInt64
NSCoder
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?
Int
n
coder.encodeObject(values, forKey: "v") 不起作用。
coder.encodeObject(values, forKey: "v")
class MyObject: NSCoding { private var values: [UInt64] // … // MARK: - NSCoding required init(coder decoder: NSCoder) { // ??? } func encodeWithCoder(coder: NSCoder) { // ??? } }
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]