xcode 检测 iPhone 24 小时制时间设置
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Detect iPhone 24-Hour time setting
提问by Darren
I'm using a UIDatePicker to select a time. I am also customising the background of the picker, however I need 2 different images depending on whether the user is using 12 hour mode (which displays AM/PM column) or 24 hour mode. How can I detect the users setting for the 12/24 hour time?
我正在使用 UIDatePicker 来选择时间。我也在自定义选择器的背景，但是我需要 2 个不同的图像，具体取决于用户是使用 12 小时模式（显示 AM/PM 列）还是 24 小时模式。如何检测 12/24 小时制的用户设置？
Thanks
谢谢
回答by Dave DeLong
Even shorter than the others:
甚至比其他人更短：
NSString *format = [NSDateFormatter dateFormatFromTemplate:@"j" options:0 locale:[NSLocale currentLocale]];
BOOL is24Hour = ([format rangeOfString:@"a"].location == NSNotFound);
Explanation
解释
The string formatting character to represent the am/pm symbol is "a", as documented in Unicode Locale Markup Language – Part 4: Dates.
表示 am/pm 符号的字符串格式化字符是“a”，如Unicode Locale Markup Language – Part 4: Dates 中所述。
The same document also explains the special template symbol "j":
同一份文件还解释了特殊的模板符号“j”：
This is a special-purpose symbol. It must not occur in pattern or skeleton data. Instead, it is reserved for use in skeletons passed to APIs doing flexible date pattern generation. In such a context, it requests the preferred hour format for the locale (h, H, K, or k), as determined by whether h, H, K, or k is used in the standard short time format for the locale. In the implementation of such an API, 'j' must be replaced by h, H, K, or k before beginning a match against availableFormats data. Note that use of 'j' in a skeleton passed to an API is the only way to have a skeleton request a locale's preferred time cycle type (12-hour or 24-hour).
这是一个特殊用途的符号。它不得出现在图案或骨架数据中。相反，它保留用于传递给执行灵活日期模式生成的 API 的骨架。在这样的上下文中，它请求区域设置的首选小时格式（h、H、K 或 k），这取决于在区域设置的标准短时间格式中是否使用 h、H、K 或 k。在此类 API 的实现中，在开始与 availableFormats 数据匹配之前，'j' 必须替换为 h、H、K 或 k。请注意，在传递给 API 的骨架中使用“j”是让骨架请求区域设置的首选时间周期类型（12 小时或 24 小时）的唯一方法。
The NSStringmethod dateFormatFromTemplate:options:locale:is described in Apple's NSDateFormatterdocumentation:
Apple 的文档中描述了该NSString方法：dateFormatFromTemplate:options:locale:NSDateFormatter
Returns a localized date format string representing the given date format components arranged appropriately for the specified locale.
返回一个本地化的日期格式字符串，表示为指定的语言环境适当排列的给定日期格式组件。
So, what that method will do is turn the @"j"you pass in as a template in to a format string suitable for NSDateFormatter. If this string contains the am / pm symbol @"a"in it anywhere, then you know the locale (and other user settings being interrogated by the OS for you) wants am / pm to be displayed.
因此，该方法将做的是将@"j"您作为模板传入的格式字符串转换为适合NSDateFormatter. 如果此字符串@"a"在任何地方包含 am / pm 符号，那么您就知道区域设置（以及操作系统为您询问的其他用户设置）希望显示 am / pm。
回答by CryingHippo
Swift (3.x) version of two most popular solutions in form of Date extension :
两个最流行的解决方案的 Swift (3.x) 版本，以 Date 扩展的形式：
extension Date {
static var is24HoursFormat_1 : Bool {
let dateString = Date.localFormatter.string(from: Date())
if dateString.contains(Date.localFormatter.amSymbol) || dateString.contains(Date.localFormatter.pmSymbol) {
return false
}
return true
}
static var is24HoursFormat_2 : Bool {
let format = DateFormatter.dateFormat(fromTemplate: "j", options: 0, locale: Locale.autoupdatingCurrent)
return !format!.contains("a")
}
private static let localFormatter : DateFormatter = {
let formatter = DateFormatter()
formatter.locale = Locale.autoupdatingCurrent
formatter.timeStyle = .short
formatter.dateStyle = .none
return formatter
}()
}
Usage :
用法 ：
Date.is24HoursFormat_1
Date.is24HoursFormat_2
Swift (2.0) version of two most popular solutions in form of NSDate extension :
NSDate 扩展形式的两个最流行的解决方案的 Swift (2.0) 版本：
extension NSDate {
class var is24HoursFormat_1 : Bool {
let dateString = NSDate.localFormatter.stringFromDate(NSDate())
if dateString.containsString(NSDate.localFormatter.AMSymbol) || dateString.containsString(NSDate.localFormatter.PMSymbol) {
return false
}
return true
}
class var is24HoursFormat_2 : Bool {
let format = NSDateFormatter.dateFormatFromTemplate("j", options: 0, locale: NSLocale.autoupdatingCurrentLocale())
return !format!.containsString("a")
}
private static let localFormatter : NSDateFormatter = {
let formatter = NSDateFormatter()
formatter.locale = NSLocale.autoupdatingCurrentLocale()
formatter.timeStyle = .ShortStyle
formatter.dateStyle = .NoStyle
return formatter
}()
}
Please note that Apple says following on NSDateFormatter (Date Formatters) :
请注意，Apple 在 NSDateFormatter ( Date Formatters)上说如下：
Creating a date formatter is not a cheap operation. If you are likely to use a formatter frequently, it is typically more efficient to cache a single instance than to create and dispose of multiple instances. One approach is to use a static variable.
创建日期格式化程序并不是一项廉价的操作。如果您可能经常使用格式化程序，则缓存单个实例通常比创建和处置多个实例更有效。一种方法是使用静态变量。
Thats the reason for static let
这就是静态 let 的原因
Secondly you should use NSLocale.autoupdatingCurrentLocale() ( for is24HoursFormat_1 ), that way you will always get the actual current state.
其次，您应该使用 NSLocale.autoupdatingCurrentLocale() （用于 is24HoursFormat_1 ），这样您将始终获得实际的当前状态。
