How do I know which is the default measure system (imperial or metric) on iOS?
How do I know which is the default measure system (imperial or metric) on iOS ?
How do I get this preference from the de开发者_运维百科vice settings, so I know what to display in my app ?
thanks
The NSLocale
can tell you:
NSLocale *locale = [NSLocale currentLocale];
BOOL isMetric = [[locale objectForKey:NSLocaleUsesMetricSystem] boolValue];
Only three countries do not use the metric system: the US, Liberia and Myanmar. The later uses its own system, the former two use Imperial Units.
Apples documentation says (emphasis mine):
NSLocaleUsesMetricSystem
The key for the flag that indicates whether the locale uses the metric system. The corresponding value is a Boolean NSNumber object. If the value is NO, you can typically assume American measurement units (for example, the statute mile).
Available in iOS 2.0 and later.
@DarkDust answer for swift3
//User region setting return
let locale = Locale.current //NSLocale.current
//Returns true if the locale uses the metric system
let isMetric = locale.usesMetricSystem
here's a swift version
var locale = NSLocale.currentLocale()
let isMetric = locale.objectForKey(NSLocaleUsesMetricSystem) as! Bool
For swift 3
let locale = NSLocale.current
let isMetric = locale.usesMetricSystem
As others mentioned before, the UK uses a mix of metric and imperial units.
I would recommend using the new MeassurementFormatter
introduced in iOS 10 which handles most of these discrepancies:
import Foundation
let locale = Locale(identifier: "EN_UK")
locale.usesMetricSystem // true!
var formatter = MeasurementFormatter()
formatter.locale = locale
formatter.string(from: Measurement(value: 1000, unit: UnitLength.meters)) // 0.621 mi
To render a distance as a string in local, natural unit, use:
let distanceInMeters: CLLocationDistance = 1000
let formatter = MeasurementFormatter()
formatter.string(from: Measurement(value: distanceInMeters, unit: UnitLength.meters)) // 0.621 mi
Official documentation: https://developer.apple.com/documentation/foundation/measurementformatter
You should probably just have a setting in your app and let your users choose -- this is what Apple does in the Weather app.
If you want to choose a sensible default you could look at the locale. If it's US, pick imperial otherwise choose metric. It is a heuristic, it will be wrong sometimes, but it's just a default that can be changed.
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