将格式化的测量值限制为2位数字 [英] Limit formatted Measurement to 2 digits

问题描述

我想基于度量"来打印字符串，但将其限制为2位数字.我为此使用 MeasurementFormatter .

I'd like to print a string based on a Measurement but limit it to 2 digits. I am using the MeasurementFormatter for this.

var beans:Measurement = Measurement(value: 20.22321, unit: UnitMass.milligrams) // "20.22321 mg"
let formatter = MeasurementFormatter()
formatter.numberFormatter.maximumFractionDigits = 2
let label = formatter.string(from: beans) // 0 lb

我希望结果为20.22 mg，而不是0 lb.我的错误在哪里?

I expected 20.22 mg as a results, not 0 lb. Where's my mistake?

推荐答案

您需要将MeasurementFormatter属性unitOptions设置为.providedUnit:

let beans = Measurement<UnitMass>(value: 20.22321, unit: .milligrams) // "20.22321 mg"
let formatter = MeasurementFormatter()
formatter.unitOptions = .providedUnit
formatter.numberFormatter.maximumFractionDigits = 2
let label = formatter.string(from: beans) // "20.22 mg"

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