如何在Swift中将数据转换为双打,Ints和字符串等类型？

Question

我正在为iOS Swift中的shapefile构建一个自定义文件打开器(一种GIS格式,与此问题无关).这些文件有一个100字节长的标题.我能够将其读入4字节数组,存储我想要的信息.我可以将这些数组转换成斯威夫特类型Data和NSData,并有转化他们(像一些其他选项Base64EncodedString).但我无法将这些原料阵列或数据或任何的格式转换成有用的属性等Double,Int和String.

import Foundation
    struct ShapeReader {
        var shapeFile = FileHandle(forReadingAtPath: "/Users/christopherjlowrie/Documents/Shapes/SF_Neighborhoods/Planning_Zones.shp")
        var fileHeader: String{
            let header = shapeFile?.readData(ofLength: 100)
            let headerStream = InputStream(data: header!)
            headerStream.open()
            var buffer = [UInt8](repeating: 0, count: 4)
            while (headerStream.hasBytesAvailable){
                headerStream.read(&buffer, maxLength: buffer.count)
                print(buffer)
                let x = Data(buffer)
                print(x)
        }
        return "A"
    }
}

这当前只返回A,因为测试原因我返回一个字符串

我怎么能打开文件,并阅读他们的原始字节分为不同的类型(Doubles,Ints,Strings)的斯威夫特？

Answer 1

你可以这样做:

要从String,Int或Double转换为数据:

Xcode 9•Swift 4 //对于旧的Swift 3语法,请单击此处

extension StringProtocol {
    var data: Data { .init(utf8) }
}

要从Data转换回String,Int或Double:

extension Numeric {
    var data: Data {
        var source = self
        // This will return 1 byte for 8-bit, 2 bytes for 16-bit, 4 bytes for 32-bit and 8 bytes for 64-bit binary integers. For floating point types it will return 4 bytes for single-precision, 8 bytes for double-precision and 16 bytes for extended precision.
        return .init(bytes: &source, count: MemoryLayout<Self>.size)
    }
}

游乐场测试

extension DataProtocol {
    var string: String? { String(bytes: self, encoding: .utf8) }
}

extension Numeric {
    init<D: DataProtocol>(_ data: D) {
        var value: Self = .zero
        let size = withUnsafeMutableBytes(of: &value, { data.copyBytes(to: $0)} )
        assert(size == MemoryLayout.size(ofValue: value))
        self = value
    }
}

extension DataProtocol {
    func value<N: Numeric>() -> N { .init(self) }
}

let value = 12.34                      // implicit Double 12.34
let data = value.data                  // double data - 8 bytes
let double = Double(data)              // implicit Double 12.34
let double1: Double = .init(data)      // explicit Double 12.34
let double2: Double = data.value()     // explicit Double 12.34
let double3 = data.value() as Double   // casting to Double 12.34