Find if user prefers 12 / 24 Hour Clock?

Question

I've got a drawRect that makes a timeline a bit like iCal. I use a for loop to write the times along a scroll view. I was wondering if A) theres a way of determining whether the user has chosen a 12 or 24 hour clock in the system settings and B) if there is a more efficient way of changing the time labels then calling an 'if' query every pass of the 'for' loop. Cheers

You need to be careful. If the user has set 12/24 hour mode in Settings contrary to the locale, then NSDateFormatter (and likely some others) ignore the presence/absence of any `a` qualifier and provide (or not) the AM/PM value based on the 12/24 hour mode setting. It's all quite screwy. — Hot Licks, May 13 '14 at 01:14

score 6 · Answer 1 · edited May 23 '17 at 12:23

The earlier answers assume that the "AM" and "PM" symbols are represented in roman characters. This code adapted from keyur bhalodiya does a better job at handling languages like Chinese, by using the AMSymbol and PMSymbol methods of NSDateFormatter.

-(BOOL)uses24hourTime
{
     NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
     [formatter setLocale:[NSLocale currentLocale]];
     [formatter setDateStyle:NSDateFormatterNoStyle];
     [formatter setTimeStyle:NSDateFormatterShortStyle];

     NSString *dateString = [formatter stringFromDate:[NSDate date]];
     NSRange amRange = [dateString rangeOfString:[formatter AMSymbol]];
     NSRange pmRange = [dateString rangeOfString:[formatter PMSymbol]];

     return (amRange.location == NSNotFound && pmRange.location == NSNotFound);
}

score 5 · Answer 2 · answered Dec 15 '11 at 14:04

5

NSDateFormatter *dateFormatter = [[[NSDateFormatter alloc] init] autorelease];
[dateFormatter setDateStyle:NSDateFormatterNoStyle];
[dateFormatter setTimeStyle:NSDateFormatterLongStyle];

if([[dateFormatter dateFormat] rangeOfString:@"a"].location != NSNotFound) {
    // user prefers 12 hour clock
} else {
    // user prefers 24 hour clock
}

answered Dec 15 '11 at 14:04

Amy Worrall

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2

This is actually the best answer, since many countries specify AM and PM as a.m. and p.m.. – MiguelB Jan 04 '12 at 17:16
1

@Leuguimerius but some languages like Chinese use totally different characters for AM and PM. See my answer http://stackoverflow.com/a/23621308/72176 for how to handle that. – William Denniss May 13 '14 at 01:12
@WilliamDenniss Brilliant! Solves everything. I had no idea such formatter existed. – MiguelB May 17 '14 at 18:36

score 1 · Accepted Answer · answered Dec 15 '11 at 14:22

NSDate *today = [NSDate date];
NSString *formattedString = [NSDateFormatter localizedStringFromDate:today dateStyle: kCFDateFormatterNoStyle timeStyle: kCFDateFormatterShortStyle];

NSRange foundRange;
foundRange = [formattedString rangeOfString:"am" options:NSCaseInsensitiveSearch];
if(foundRange.location == NSNotFound) {
    foundRange = [formattedString rangeOfString:"pm" options:NSCaseInsensitiveSearch];
}

BOOL isAMPMSettingOn = (foundRange.location != NSNotFound);

Find if user prefers 12 / 24 Hour Clock?

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