What is the best way to deal with the NSDateFormatter locale "feechur"?

Question

It seems that NSDateFormatter has a "feature" that bites you unexpectedly: If you do a simple "fixed" format operation such as:

NSDateFormatter* fmt = [[NSDateFormatter alloc] init];
[fmt setDateFormat:@"yyyyMMddHHmmss"];
NSString* dateStr = [fmt stringFromDate:someDate];
[fmt release];

Then it works fine in the US and most locales UNTIL ... someone with their phone set to a 24-hour region sets the 12/24 hour switch in settings to 12. Then the above starts tacking "AM" or "PM" onto the end of the resulting string.

(See, eg, NSDateFormatter, am I doing something wrong or is this a bug?)

(And see https://developer.apple.com/library/content/qa/qa1480/_index.html)

Apparently Apple has declared this to be "BAD" -- Broken As Designed, and they aren't going to fix it.

The circumvention is apparently to set the locale of the date formatter for a specific region, generally the US, but this is a bit messy:

NSLocale *loc = [[NSLocale alloc] initWithLocaleIdentifier:@"en_US"];
[df setLocale: loc];
[loc release];

Not too bad in onesies-twosies, but I'm dealing with about ten different apps, and the first one I look at has 43 instances of this scenario.

So any clever ideas for a macro/overridden class/whatever to minimize the effort to change everything, without making the code to obscure? (My first instinct is to override NSDateFormatter with a version that would set the locale in the init method. Requires changing two lines -- the alloc/init line and the added import.)

##Added

This is what I've come up with so far -- seems to work in all scenarios:

@implementation BNSDateFormatter

-(id)init {
static NSLocale* en_US_POSIX = nil;
NSDateFormatter* me = [super init];
if (en_US_POSIX == nil) {
    en_US_POSIX = [[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"];
}
[me setLocale:en_US_POSIX];
return me;
}

@end

##Update Re OMZ's proposal, here is what I'm finding --

Here is the category version -- h file:

#import <Foundation/Foundation.h>


@interface NSDateFormatter (Locale)
- (id)initWithSafeLocale;
@end

Category m file:

#import "NSDateFormatter+Locale.h"


@implementation NSDateFormatter (Locale)

- (id)initWithSafeLocale {
static NSLocale* en_US_POSIX = nil;
self = [super init];
if (en_US_POSIX == nil) {
    en_US_POSIX = [[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"];
}
NSLog(@"Category's locale: %@ %@", en_US_POSIX.description, [en_US_POSIX localeIdentifier]);
[self setLocale:en_US_POSIX];
return self;    
}

@end

The code:

NSDateFormatter* fmt;
NSString* dateString;
NSDate* date1;
NSDate* date2;
NSDate* date3;
NSDate* date4;

fmt = [[NSDateFormatter alloc] initWithSafeLocale];
[fmt setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
dateString = [fmt stringFromDate:[NSDate date]];
NSLog(@"dateString = %@", dateString);
date1 = [fmt dateFromString:@"2001-05-05 12:34:56"];
NSLog(@"date1 = %@", date1.description);
date2 = [fmt dateFromString:@"2001-05-05 22:34:56"];
NSLog(@"date2 = %@", date2.description);
date3 = [fmt dateFromString:@"2001-05-05 12:34:56PM"];  
NSLog(@"date3 = %@", date3.description);
date4 = [fmt dateFromString:@"2001-05-05 12:34:56 PM"]; 
NSLog(@"date4 = %@", date4.description);
[fmt release];

fmt = [[BNSDateFormatter alloc] init];
[fmt setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
dateString = [fmt stringFromDate:[NSDate date]];
NSLog(@"dateString = %@", dateString);
date1 = [fmt dateFromString:@"2001-05-05 12:34:56"];
NSLog(@"date1 = %@", date1.description);
date2 = [fmt dateFromString:@"2001-05-05 22:34:56"];
NSLog(@"date2 = %@", date2.description);
date3 = [fmt dateFromString:@"2001-05-05 12:34:56PM"];  
NSLog(@"date3 = %@", date3.description);
date4 = [fmt dateFromString:@"2001-05-05 12:34:56 PM"]; 
NSLog(@"date4 = %@", date4.description);
[fmt release];

The result:

2011-07-11 17:44:43.243 DemoApp[160:307] Category's locale: <__NSCFLocale: 0x11a820> en_US_POSIX
2011-07-11 17:44:43.257 DemoApp[160:307] dateString = 2011-07-11 05:44:43 PM
2011-07-11 17:44:43.264 DemoApp[160:307] date1 = (null)
2011-07-11 17:44:43.272 DemoApp[160:307] date2 = (null)
2011-07-11 17:44:43.280 DemoApp[160:307] date3 = (null)
2011-07-11 17:44:43.298 DemoApp[160:307] date4 = 2001-05-05 05:34:56 PM +0000
2011-07-11 17:44:43.311 DemoApp[160:307] Extended class's locale: <__NSCFLocale: 0x11a820> en_US_POSIX
2011-07-11 17:44:43.336 DemoApp[160:307] dateString = 2011-07-11 17:44:43
2011-07-11 17:44:43.352 DemoApp[160:307] date1 = 2001-05-05 05:34:56 PM +0000
2011-07-11 17:44:43.369 DemoApp[160:307] date2 = 2001-05-06 03:34:56 AM +0000
2011-07-11 17:44:43.380 DemoApp[160:307] date3 = (null)
2011-07-11 17:44:43.392 DemoApp[160:307] date4 = (null)

The phone [make that an iPod Touch] is set to Great Britain, with the 12/24 switch set to 12. There's a clear difference in the two results, and I judge the category version to be wrong. Note that the log in the category version IS getting executed (and stops placed in the code are hit), so it's not simply a case of the code somehow not getting used.

##A curious observation

Modified the category implementation slightly:

#import "NSDateFormatter+Locale.h"

@implementation NSDateFormatter (Locale)

- (id)initWithSafeLocale {
static NSLocale* en_US_POSIX2 = nil;
self = [super init];
if (en_US_POSIX2 == nil) {
    en_US_POSIX2 = [[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"];
}
NSLog(@"Category's locale: %@ %@", en_US_POSIX2.description, [en_US_POSIX2 localeIdentifier]);
[self setLocale:en_US_POSIX2];
NSLog(@"Category's object: %@ and object's locale: %@ %@", self.description, self.locale.description, [self.locale localeIdentifier]);
return self;    
}

@end

Basically just changed the name of the static locale variable (in case there was some conflict with the static declared in the subclass) and added the extra NSLog. But look what that NSLog prints:

2011-07-15 16:35:24.322 DemoApp[214:307] Category's locale: <__NSCFLocale: 0x160550> en_US_POSIX
2011-07-15 16:35:24.338 DemoApp[214:307] Category's object: <NSDateFormatter: 0x160d90> and object's locale: <__NSCFLocale: 0x12be70> en_GB
2011-07-15 16:35:24.345 DemoApp[214:307] dateString = 2011-07-15 04:35:24 PM
2011-07-15 16:35:24.370 DemoApp[214:307] date1 = (null)
2011-07-15 16:35:24.378 DemoApp[214:307] date2 = (null)
2011-07-15 16:35:24.390 DemoApp[214:307] date3 = (null)
2011-07-15 16:35:24.404 DemoApp[214:307] date4 = 2001-05-05 05:34:56 PM +0000

As you can see, the setLocale simply didn't. The locale of the formatter is still en_GB. It appears that there is something "strange" about an init method in a category.

Answer 1

Duh!!

Sometimes you have an "Aha!!" moment, sometimes it's more of a "Duh!!" This is the latter. In the category for initWithSafeLocale the "super" init was coded as self = [super init];. This inits the SUPERCLASS of NSDateFormatter but does not init the NSDateFormatter object itself.

Apparently when this initialization is skipped, setLocale "bounces off", presumably because of some missing data structure in the object. Changing the init to self = [self init]; causes the NSDateFormatter initialization to occur, and setLocale is happy again.

Here is the "final" source for the category's .m:

#import "NSDateFormatter+Locale.h"

@implementation NSDateFormatter (Locale)

- (id)initWithSafeLocale {
    static NSLocale* en_US_POSIX = nil;
    self = [self init];
    if (en_US_POSIX == nil) {
        en_US_POSIX = [[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"];
    }
    [self setLocale:en_US_POSIX];
    return self;    
}

@end

Answer 2

Instead of subclassing, you could create an NSDateFormatter category with an additional initializer that takes care of assigning the locale and possibly also a format string, so you'd have a ready-to-use formatter right after initializing it.

@interface NSDateFormatter (LocaleAdditions)

- (id)initWithPOSIXLocaleAndFormat:(NSString *)formatString;

@end

@implementation NSDateFormatter (LocaleAdditions)

- (id)initWithPOSIXLocaleAndFormat:(NSString *)formatString {
    self = [super init];
    if (self) {
        NSLocale *locale = [[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"];
        [self setLocale:locale];
        [locale release];
        [self setFormat:formatString];
    }
    return self;
}

@end

Then you could use NSDateFormatter anywhere in your code with just:

NSDateFormatter* fmt = [[NSDateFormatter alloc] initWithPOSIXLocaleAndFormat:@"yyyyMMddHHmmss"];

You might want to prefix your category method somehow to avoid name conflicts, just in case Apple decides to add such a method in a future version of the OS.

In case you're always using the same date format(s), you could also add category methods that return singleton instances with certain configurations (something like +sharedRFC3339DateFormatter). Be aware however that NSDateFormatter is not thread-safe and you have to use locks or @synchronized blocks when you're using the same instance from multiple threads.