NSDateFormatter reuse

gistfile1.m

// For NSString to NSDate to parse server dates in the full ISO 8601 format
// E.g. 2014-02-11T10:22:46+00:00
+ (NSDateFormatter *) iso8601FullDateFromatter
{
    static NSDateFormatter * dateFormatter;
    
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        
        dateFormatter = [[NSDateFormatter alloc] init];
        
        [dateFormatter setDateFormat:@"yyyy-MM-dd'T'HH:mm:ssZ"];
        
        [dateFormatter setCalendar:[[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar]];
        [dateFormatter setLocale:[[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"]];
        [dateFormatter setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0]];
    });
    
    return dateFormatter;
}

// For NSDate to NSString to display to the user
// E.g. 'Nov 23, 1937'
+ (NSDateFormatter *) userOutputDateOnlyFormatter
{
    static NSDateFormatter * dateFormatter;
    
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        
        dateFormatter = [[NSDateFormatter alloc] init];
        
        [dateFormatter setDateStyle:NSDateFormatterMediumStyle];
        [dateFormatter setTimeStyle:NSDateFormatterNoStyle];
        
        [dateFormatter setCalendar:[NSCalendar currentCalendar]];
        [dateFormatter setLocale:[NSLocale currentLocale]];
        [dateFormatter setTimeZone:[NSTimeZone defaultTimeZone]];
    });
    
    return dateFormatter;
}

This is an example of how you should configure NSDateFormatter objects properties for two separate purposes. It also demonstrates a reuse pattern to avoid performance issues.

It is part of my blog post on NSDateFormatters
http://www.rsaunders.co.uk/2014/02/date-parsing.html