如何从测量中获取格式化的值和单位

问题描述：

我试图从测量中获取格式化的值，将单位作为两个单独的字符串。我已经写了下面的功能来做到这一点。我正在努力处理模板的扩展的函数格式。如何从测量中获取格式化的值和单位

这不起作用：

func getFormattedValueAndUnitFromMeasurement(measurement: Measurement<Unit>)

下面的作品，但后来我需要定义功能为每个单位类型。

func getFormattedValueAndUnitFromMeasurement(measurement: Measurement<UnitLength>)

这是我使用的代码。

var diameter: Measurement<UnitLength> = Measurement<UnitLength>(value: 13, unit: .inches) 

let diameterFormatter = MeasurementFormatter() 
diameterFormatter.unitStyle = .medium 
diameterFormatter.unitOptions = .providedUnit // .natural 
diameterFormatter.numberFormatter.generatesDecimalNumbers = true 
diameterFormatter.numberFormatter.maximumFractionDigits = 1 

    // Get the formatted text for the value and the units 
let diameterText = diameterFormatter.getFormattedValueAndUnitFromMeasurement(measurement: diameter) 


extension MeasurementFormatter { 
    func getFormattedValueAndUnitFromMeasurement(measurement: Measurement<Unit>) -> (valueString: String, unitString: String) 
    { 
     // Number Formatter 
     let numberFormatter = self.numberFormatter 

     // This assumes the number is going to be displayed in the provided units. Ok for now 
     let numberString = numberFormatter?.string(from: NSNumber (value: measurement.value)) 

     // Figure out just the units of the string 
     var units: String = self.string(for: measurement)! 

     if (units.hasPrefix(numberString!)) { 
      units.removeSubrange((numberString?.startIndex)! ..< (numberString?.index((numberString?.startIndex)!, offsetBy: (numberString?.characters.count)!))!) 
     } 

     return (numberString!, units) 
    } 
}

答

Measurement<Unit>和Measurement<UnitLength>被认为是两种不同的类型，如String和Int。您应该使用泛型来处理所需的类型，例如

func getFormattedValueAndUnitFromMeasurement<T>(measurement: Measurement<T>)  
               -> (valueString: String, unitString: String)

如何从测量中获取格式化的值和单位

相关推荐