Trying to use NSDate for time only - ios

Question

I'm struggling to find a way to use NSDate for time only purposes.
I was trying to do the following code:
- (void)awakeFromInsert
{
NSDateComponents *comps = [[NSDateComponents alloc] init];
comps.minute = 45;
comps.second = 0;
NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
self.periodDuration = [calendar dateFromComponents:comps];
NSLog(#"periodDuration: %#",self.periodDuration);
comps = [[NSDateComponents alloc] init];
comps.hour = 8;
comps.minute = 0;
self.firstPeriodStartTime = [calendar dateFromComponents:comps];
NSLog(#"firstPeriodTime: %#",self.periodDuration);
}
But the result I get is:
periodDuration: 0001-12-31 22:24:04 +0000
firstPeriodTime: 0001-12-31 22:24:04 +0000
The result I was expecting:
periodDuration: 45:00
firstPeriodTime: 08:00
What am I doing wrong? How can I fix this?
Thank you.

Answer 1

The log of date is misleading you, if you are forming a date with only a few components you will not get a proper date instance which uniquely identifies a date and time.
If you try with this code snipped you can find that if you are just converting the dates back to string it is just as you expect
NSDateComponents *comps = [[NSDateComponents alloc] init];
comps.minute = 45;
comps.second = 0;
NSCalendar *calendar = [NSCalendar currentCalendar];
NSDate *periodDate = [calendar dateFromComponents:comps];
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:#"mm:ss"];
NSLog(#"periodDuration: %#",[dateFormatter stringFromDate:periodDate]);
comps = [[NSDateComponents alloc] init];
comps.hour = 8;
comps.minute = 0;
NSDate *firstPeriodDate = [calendar dateFromComponents:comps];
[dateFormatter setDateFormat:#"HH:mm"];
NSLog(#"firstPeriodTime: %#",[dateFormatter stringFromDate:firstPeriodDate]);
periodDuration: 45:00
firstPeriodTime: 08:00

Answer 2

You can use NSDateFormatter
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:#"HH:mm"];
NSLog(#"%#",[dateFormatter stringFromDate:[NSDate date]]);

Answer 3

Use a NSTimeInterval (which is, basically, a double containing the number of seconds). To store it in CoreData:
[NSNumber numberWithDouble:myTimeInterval];
As for formatting: If you want more than 24h displayed, use this:
NSUInteger seconds = (NSUInteger)round(myTimeInterval);
NSString *formattedDate = [NSString stringWithFormat:#"%02u:%02u:%02u",
seconds / 3600, (seconds / 60) % 60, seconds % 60];
NSLog(#"%#", formattedDate);
If you don't want more than 24h, you can use NSDate and NSDateFormatter again:
NSDate *date = [NSDate dateWithTimeIntervalSinceReferenceDate:myTimeInterval];
NSDateFormatter *dateFormatter = [NSDateFormatter new];
[dateFormatter setDateFormat:#"HH:mm:ss"];
[dateFormatter setTimeZone:[NSTimeZone timeZoneWithName:#"UTC"]];
NSString *formattedDate = [dateFormatter stringFromDate:date];
NSLog(#"%#", formattedDate);

Answer 4

NSString *timeString;
timeString = [NSDateFormatter localizedStringFromDate:[NSDate date]
dateStyle:NSDateFormatterNoStyle
timeStyle:NSDateFormatterMediumStyle];
12:03:54 PM