如何在Swift中将数据转换为双打,Ints和字符串等类型？

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为Swift类型Data和NSData,并有一些其他选项可以转换它们(如Base64EncodedString).但是我无法将这些原始数组或数据或任何格式转换为有用的属性,如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

如何打开文件,并将其原始字节读入Swift中的类型(双打,Ints,字符串)？

解决方法

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语法单击here

extension String {
    var data: Data { return Data(utf8) }
}

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 Data(bytes: &source,count: MemoryLayout<Self>.size)  
    }
}

要从Data转换回String,Int或Double：

extension Data {
    var integer: Int {
        return withUnsafeBytes { $0.pointee }
    }
    var int32: Int32 {
        return withUnsafeBytes { $0.pointee }
    }
    var float: Float {
        return withUnsafeBytes { $0.pointee }
    }
    var float80: Float80 {
        return withUnsafeBytes { $0.pointee }
    }
    var double: Double {
        return withUnsafeBytes { $0.pointee }
    }
    var string: String {
        return String(data: self,encoding: .utf8) ?? ""
    }
}

游乐场测试

let intData = 1_234_567_890_123_456_789.data    // 8 bytes (64 bit Integer)
let dataToInt = intData.integer                 // 1234567890123456789

let intMinData = Int.min.data                   // 8 bytes (64 bit Integer)
let backToIntMin = intMinData.integer           // -9223372036854775808

let intMaxData = Int.max.data                   // 8 bytes (64 bit Integer)
let backToIntMax = intMaxData.integer           // 9223372036854775807

let myInt32Data = Int32(1_234_567_890).data     // 4 bytes (32 bit Integer)
let backToInt32 = myInt32Data.int32             // 1234567890

let int32MinData = Int32.min.data               // 4 bytes (32 bit Integer)
let backToInt32Min = int32MinData.int32         // -2147483648

let int32MaxData = Int32.max.data               // 4 bytes (32 bit Integer)
let backToInt32Max = int32MaxData.int32         // 2147483647

let myFloatData = Float.pi.data                 // 4 bytes (32 bit single=precison FloatingPoint)
let backToFloat = myFloatData.float             // 3.141593
backToFloat == .pi      // true

let myDoubleData = Double.pi.data               // 8 bytes (64 bit double-precision FloatingPoint)
let backTodouble = myDoubleData.double          // 3.141592653589793
backTodouble == .pi     // true

let myFloat80Data = Float80.pi.data             // 16 bytes (128 bit extended-precision FloatingPoint)
let backToFloat80 = myFloat80Data.float80       // 3.141592653589793116
backToFloat80 == .pi    // true

let myStringData = Data("Hello World !!!".data.prefix(4))   // 4 bytes
let backToString = myStringData.string                      //  "Hell"