Converting time to HH:MM - objective-c

Question

I currently have a float value like 12.5, 4, 17.5. I want these to correspond to the times 12:30PM, 4:00AM, and 5:30PM.
I've currently achieved something close to this with the hack
if (time > 12.5) {
time = abs(roundedValue - 12);
[lab setText:[NSString stringWithFormat:#"%i:00PM",(int)time]];
} else {
[lab setText:[NSString stringWithFormat:#"%i:00AM",(int)time]];
}
But I know this is bad practice. What's a better way to convert these numbers to times?

Answer 1

This is just basic math, you have a value, say 12.5, which consists of a number of hours, 12, and a fraction of an hour, 0.5. There are 60 mins in an hour so the number of minutes is just the fraction times 60.
If you want to use the 12 hour clock there is a small quirk, hours > 12 need to be reduced by 12 but noon (12) is pm and midnight (0 or 24) is am. So the test for am/pm is not the same test as whether to subtract 12.
Here is one way to do it (with minimal checking):
NSString *hoursToString(double floatHours)
{
int hours = trunc(floatHours); // number of hours
int mins = round( (floatHours - hours) * 60 ); // mins is the fractional part times 60
// rounding might result in 60 mins...
if (mins == 60)
{
mins = 0;
hours++;
}
// we haven't done a range check on floatHours, also the above can add 1, so reduce to 0 -> 23
hours %= 24;
// if you are using 24 hour clock you can finish here and format to the two values
BOOL pm = hours >= 12; // 0 - 11 = am, 12 - 23 = pm
if (hours > 12) hours -= 12; // 13 - 23 -> 1 -> 11
return [NSString stringWithFormat:#"%d:%02d %s", hours, mins, (pm ? "pm" : "am")];
}
You call this simply as:
hoursToString(13.1) // returns 1:06 pm
No need to use NSDate et al.
HTH

Answer 2

Solved by doing the following:
NSDate *now = [NSDate date];
NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian];
NSDateComponents *components = [calendar components:NSCalendarUnitYear|NSCalendarUnitMonth|NSCalendarUnitDay fromDate:now];
[components setHour:0];
NSDate *today10am = [calendar dateFromComponents:components];
NSDate *newDate = [NSDate dateWithTimeInterval:roundedValue*60*60 sinceDate:today10am];
NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
[dateFormat setDateFormat:#"h:mm aa"];
[lab setText:[dateFormat stringFromDate:newDate]];
Sorry Hot Licks, guess this was within my comprehension.

Answer 3

You can use the following -
NSNumber *time = [NSNumber numberWithDouble:([yourTime doubleValue] - 3600)];
NSTimeInterval interval = [time doubleValue];
NSDate *yourDate = [NSDate date];
yourDate = [NSDate dateWithTimeIntervalSince1970:interval];
NSDateFormatter *dateFormatter = [[[NSDateFormatter alloc] init] autorelease];
[dateFormatter setDateFormat:#"HH:mm:ss"];
NSLog(#"result: %#", [dateFormatter stringFromDate:yourDate]);