How do I break down an NSTimeInterval into year, months, days, hours, minutes and seconds on iPhone?

Question

I have a time interval that spans years and I want all the time components from year down to seconds.

My first thought is to integer divide the time interval by seconds in a year, subtract that from a running total of seconds, divide that by seconds in a month, subtract that from the running total and so on.

That just seems convoluted and I've read that whenever you are doing something that looks convoluted, there is probably a built-in method.

Is there?

I integrated Alex's 2nd method into my code.

It's in a method called by a UIDatePicker in my interface.

NSDate *now = [NSDate date];
NSDate *then = self.datePicker.date;
NSTimeInterval howLong = [now timeIntervalSinceDate:then];

NSDate *date = [NSDate dateWithTimeIntervalSince1970:howLong];
NSString *dateStr = [date description];
const char *dateStrPtr = [dateStr UTF8String];
int year, month, day, hour, minute, sec;

sscanf(dateStrPtr, "%d-%d-%d %d:%d:%d", &year, &month, &day, &hour, &minute, &sec);
year -= 1970;

NSLog(@"%d years\n%d months\n%d days\n%d hours\n%d minutes\n%d seconds", year, month, day, hour, minute, sec);

When I set the date picker to a date 1 year and 1 day in the past, I get:

1 years 1 months 1 days 16 hours 0 minutes 20 seconds

which is 1 month and 16 hours off. If I set the date picker to 1 day in the past, I am off by the same amount.

Update: I have an app that calculates your age in years, given your birthday (set from a UIDatePicker), yet it was often off. This proves there was an inaccuracy, but I can't figure out where it comes from, can you?

Answer 1

Convert your interval into an NSDate using +dateWithIntervalSince1970, get the date components out of that using NSCalendar's -componentsFromDate method.

SDK Reference

Answer 2

NSDate *date = [NSDate dateWithTimeIntervalSince1970:timeInterval];

// format: YYYY-MM-DD HH:MM:SS ±HHMM
NSString *dateStr = [date description];
NSRange range;

// year
range.location = 0;
range.length = 4;
NSString *yearStr = [dateStr substringWithRange:range];
int year = [yearStr intValue] - 1970;

// month
range.location = 5;
range.length = 2;
NSString *monthStr = [dateStr substringWithRange:range];
int month = [monthStr intValue];

// day, etc.
...

Answer 3

Here's another possibility, somewhat cleaner:

NSDate *date = [NSDate dateWithTimeIntervalSince1970:timeInterval];
NSString *dateStr = [date description];
const char *dateStrPtr = [dateStr UTF8String];

// format: YYYY-MM-DD HH:MM:SS ±HHMM
int year, month, day, hour, minutes, seconds;
sscanf(dateStrPtr, "%d-%d-%d %d:%d:%d", &year, &month, &day, &hour, &minutes, &seconds);
year -= 1970;

Answer 4

Brief Description

1. Just another approach to complete the answer of JBRWilkinson but adding some code. It can also offers a solution to Alex Reynolds's comment.

2. Use NSCalendar method:

   • (NSDateComponents *)components:(NSUInteger)unitFlags fromDate:(NSDate *)startingDate toDate:(NSDate *)resultDate options:(NSUInteger)opts

   • "Returns, as an NSDateComponents object using specified components, the difference between two supplied dates". (From the API documentation).

3. Create 2 NSDate whose difference is the NSTimeInterval you want to break down. (If your NSTimeInterval comes from comparing 2 NSDate you don't need to do this step, and you don't even need the NSTimeInterval, just apply the dates to the NSCalendar method).

4. Get your quotes from NSDateComponents

Sample Code

// The time interval 
NSTimeInterval theTimeInterval = ...;

// Get the system calendar
NSCalendar *sysCalendar = [NSCalendar currentCalendar];

// Create the NSDates
NSDate *date1 = [[NSDate alloc] init];
NSDate *date2 = [[NSDate alloc] initWithTimeInterval:theTimeInterval sinceDate:date1]; 

// Get conversion to months, days, hours, minutes
unsigned int unitFlags = NSHourCalendarUnit | NSMinuteCalendarUnit | NSDayCalendarUnit | NSMonthCalendarUnit;

NSDateComponents *breakdownInfo = [sysCalendar components:unitFlags fromDate:date1  toDate:date2  options:0];

NSLog(@"Break down: %dmin %dhours %ddays %dmoths",[breakdownInfo minute], [breakdownInfo hour], [breakdownInfo day], [breakdownInfo month]);

[date1 release];
[date2 release];

Answer 5

This works for me:

    float *lenghInSeconds = 2345.234513;
    NSDate *date = [NSDate dateWithTimeIntervalSinceReferenceDate:lenghInSeconds];
    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];


    [formatter setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0.0]];

    [formatter setDateFormat:@"HH:mm:ss"];
    NSLog(@"%@", [formatter stringFromDate:date]); 
    [formatter release];

The main difference here is that you need to adjust for the timezone.