How to format data from string variable - iphone

Question

I have a NSString that keeps date:
1900-01-01T11:00:00
I need to format it, so I have a formatter:
NSDateFormatter *df = [[NSDateFormatter alloc] init];
[df setDateFormat:#"dd/MM/yyyy hh:mm:ss a"];
How to format this string now?
NSString* formatedDateString = [df ???];

Answer 1

Create a date formatter, that returns a date object for for the given string, create a second date formatter, that returns a string in the desired format from that date.
NSDateformatter *inputFormatter = [[NSDateformatter alloc] init];
[inputFormatter setDateFormat:#"yyyy-MM-dd'T'HH:mm:ss"];
[inputFormatter setLocale:[[NSLocale alloc] initWithLocaleIdentifier:#"en_US_POSIX"]];
NSDate *date = [inputFormatter dateFromString:dateString];
NSDateformatter *outputFormatter = [[NSDateformatter alloc] init];
[outputFormatter setLocale:[[NSLocale alloc] initWithLocaleIdentifier:#"en_US_POSIX"]];
[outputFormatter setDateFormat:#"dd/MM/yyyy hh:mm:ss a"];
NSString *outputString = [outputFormatter stringFromDate:date];
But you could also let the output date formatter decide the style in respect to the locale:
NSDateformatter *outputFormatter = [[NSDateformatter alloc] init];
[outputFormatter setDateStyle:NSDateFormatterShortStyle];
[outputFormatter setTimeStyle:NSDateFormatterShortStyle];
NSString *outputString = [outputFormatter stringFromDate:date];
for a american locale, you should now cat the desired format.
if you want to enforce format "dd/MM/yyyy hh:mm:ss a" for the user, you should also set the locale of the output date formatter.
a complete command line example.
int main(int argc, const char * argv[])
{
#autoreleasepool {
NSString *dateString1 = #"2012-12-31T11:00:00";
NSString *dateString2 = #"2012-12-31T14:00:00";
NSDateFormatter *inputFormatter = [[NSDateFormatter alloc] init];
[inputFormatter setLocale:[[NSLocale alloc] initWithLocaleIdentifier:#"en_US_POSIX"]];
[inputFormatter setDateFormat:#"yyyy-MM-dd'T'HH:mm:ss"];
NSDateFormatter *outputFormatter = [[NSDateFormatter alloc] init];
[outputFormatter setLocale:[[NSLocale alloc] initWithLocaleIdentifier:#"en_US_POSIX"]];
[outputFormatter setDateFormat:#"dd/MM/yyyy hh:mm:ss a"];
NSDate *date1 = [inputFormatter dateFromString:dateString1];
NSDate *date2 = [inputFormatter dateFromString:dateString2];
NSString *outputString1 = [outputFormatter stringFromDate:date1];
NSString *outputString2 = [outputFormatter stringFromDate:date2];
NSLog(#"%#", outputString1);
NSLog(#"%#", outputString2);
}
return 0;
}
If you dont set the locale like [outputFormatter setLocale:[[NSLocale alloc] initWithLocaleIdentifier:#"en_US_POSIX"]]; it will lead do a ugly mix of formats with user's sefault locale, if it not happend to be 'en_US'
ie in German: 31/12/2012 02:00:00 nachm. This is a format not used in german.
To support user's language and locale you should instead use the different styles.
The q&a rmaddy provided indicates, that there are rare cases, where the parse format gets rewritten. To avoid this, set the input formatted's format to a certain locale, like [inputFormatter setLocale:[[NSLocale alloc] initWithLocaleIdentifier:#"en_US_POSIX"]];

Answer 2

You need to create two date formatter, one for parsing, one for formatting; Your parsing format is "yyyy-MM-ddThh:mm:ss" and your output format is "dd/MM/yyyy hh:mm:ss a". So, something like this :
NSString * targetString = #"1900-01-01'T'11:00:00";
NSDateFormatter *parseFormat = [[NSDateFormatter alloc] init];
[parseFormat setDateFormat:#"yyyy-MM-ddThh:mm:ss"];
NSDate * date = [parseFormat dateFromString:targetString];
NSDateFormatter * outputFormat = [[NSDateFormatter alloc] init];
[outputFormat setDateFormat:#"dd/MM/yyyy hh:mm:ss a";
NSString * outputString = [parseFormat stringFromDate:date];

Answer 3

example for getting current date :
-(void) getDate
{
NSString *theDate;
NSString *theTime;
NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
[dateFormat setDateFormat:#"yyyy-MM-dd"];
NSDateFormatter *timeFormat = [[NSDateFormatter alloc] init];
[timeFormat setDateFormat:#"HH:mm:ss"];
NSDate *now = [[NSDate alloc] init];
theDate = [dateFormat stringFromDate:now];
theTime = [timeFormat stringFromDate:now];
//2012-09-21 02:00:00
self.deviceCurrentTime=[NSString stringWithFormat:#"%# %#",theDate,theTime];
}