Measurements and Units

一、相关类

Dimension 是units的分类。比如长度，时间，速度。
长度：km，m，ft，mi，etc
有一个默认的基本单位：let meter = UnitLength.baseUnit
可以转换单位 km <=>ft, m <=> mi

dimension.png

// Measurement

public struct Measurement<UnitType : Unit> : Comparable, Equatable { 
    public let unit: UnitType 
    public var value: Double 
    public init(value: Double, unit: UnitType)
}

// Calculations With Measurements

 let distanceTraveled = Measurement(value: 5, unit: UnitLength.feet)
 let distanceToGo = Measurement(value: 6, unit: UnitLength.feet)
 let totalDistance = distanceTraveled + distanceToGo

// Unit

public class Unit : NSObject, NSCopying { 
    public let symbol : String 
    public init(symbol: String)
}

// Dimension

public class Dimension : Unit, NSCoding { 
    public var converter : UnitConverter { get } 
    public init(symbol: String, converter: UnitConverter)
    public class var baseUnit : Dimension
}

public class UnitLength : Dimension {/*
     Base unit - meters */
     public class var kilometers: UnitLength { get }
     public class var meters: UnitLength { get }
     public class var feet: UnitLength { get }
     public class var miles: UnitLength { get }
...}

二、自定义单位

单位转换: baseUnit <=>unit

• UnitConverter

• baseUnitValue(fromValue value:)

• value(fromBaseUnitValue baseUnitValue:)

• UnitConverterLinear

• baseUnitValue = value * coefficient + constant

• value = (baseUnitValue - constant)/coefficient

// “Jammin’ in the Streetz” Game - Custom Units
 
let jamz = UnitDuration(symbol: “jamz", converter: UnitConverterLinear(coefficient: 30))
let hopz = UnitLength(symbol: “hopz", converter: UnitConverterLinear(coefficient: 0.75))
let glidez = UnitLength(symbol: “glidez", converter: UnitConverterLinear(coefficient: 1.5))


// “Jammin’ in the Streetz” Game - Custom Dimension

238_MeasurementsAndUnits_Final.key

public class UnitDanceMove : Dimension {
    static let wackyArmMovements = UnitDanceMove(symbol: "💪",converter: UnitConverterLinear(coefficient: 1))
    static let robot = UnitDanceMove(symbol: "🤖",converter: UnitConverterLinear(coefficient: 4))
    static let cabbagePatch = UnitDanceMove(symbol: "👼", converter: UnitConverterLinear(coefficient: 3))
    static let jazzHands = UnitDanceMove(symbol: "👐",converter: UnitConverterLinear(coefficient: 2))
}

// “Jammin’ in the Streetz” Game - Jam Session

public struct JamSession { 
    public var stepsTaken : Measurement<UnitLength> 
    public var jamTime : Measurement<UnitDuration> 
    public var danceMoves : Measurement<UnitDanceMove> 
    public var danceRate : Measurement<UnitSpeed> {
       let stepsInMeters = stepsTaken.converted(to: .meters) 
       let jamTimeInSeconds = jamTime.converted(to: .seconds) 
       return Measurement(value: (stepsInMeters.value / jamTimeInSeconds.value),
      }
}

三、格式化

unit options.png

// MeasurementFormatter

public class MeasurementFormatter : Formatter, NSSecureCoding { 
    public var unitOptions: MeasurementFormatter.UnitOptions 
    public var unitStyle: Formatter.UnitStyle 
    @NSCopying public var locale: Locale!
    @NSCopying public var numberFormatter: NumberFormatter! 
    public func string(from measurement: Measurement<Unit>) -> String
    public func string(from unit: Unit) -> String
}

// 1.系统实现的单位，结果为系统符号
let formatter = MeasurementFormatter()
let distance = Measurement(value: 5, unit: UnitLength.kilometers)
let result = formatter.string(from: distance)

// 2.自定义系统实现的单位，结果为系统符号
let hopz = UnitLength(symbol: “hopz", converter: UnitConverterLinear(coefficient: 0.75))
let hopzDistance = Measurement(value: 1000, unit: hope)
let resultingHopz = formatter.string(from: hopzDistance)

// 3.自定义系统实现的单位，设置unitOptions，结果为自定义符号
formatter.unitOptions = [.providedUnit]
let hopzDistance = Measurement(value: 1000, unit: hope)
let resultingHopz = formatter.string(from: hopzDistance)

// 4.完全自定义单位，结果为自定义符号
let robotDance = Measurement(value: 30, unit: UnitDanceMove.robot)
let resultingRobotDances = formatter.string(from: robotDance)