ios - iOS MeasurementFormatter中的零符号

Question

使用MeasurementFormatter时，我在声明/使用零符号表示未知值时遇到问题:

let numberFormatter = NumberFormatter()
numberFormatter.numberStyle = .decimal
numberFormatter.zeroSymbol = "?"

numberFormatter.string(from: 0.0) // '?'

let formatter = MeasurementFormatter()
formatter.unitOptions = .providedUnit
formatter.numberFormatter = numberFormatter

var distance = Measurement<UnitLength>(value: 0, unit: .parsecs)
formatter.string(from: distance) // '0 pc' - expected: '? pc'

尝试使用不同的值声明(例如Double.zero)不会更改输出。
这是iOS中的概念性事情，还是我在这里遗漏了一些东西？

Answer 1

It turned out通过更改Measurement声明(distance)产生所需的输出:

let dist1 = Measurement<UnitLength>(value: 0, unit: .parsecs) // output: '0 pc'
let dist2 = Measurement(value: 0, unit: Unit(symbol: UnitLength.parsecs.symbol)) // output '? pc' as expected

提交了radar。