I am using
NSDate *date = [NSDate date];
for getting the date, but the date I get is off by 2 hours.
NSDate objects don't have time zones. They represent an absolute moment in time. However, when you ask one for its description (by printing it with NSLog(), e.g.), it has to pick a time zone. The most reasonable "default" choice is GMT. If you're not in GMT yourself, the date will seem to be incorrect, by the amount of your own offset.
You should always use an NSDateFormatter to create a string for display. The formatter's timezone should be set to yours, which is the default.
You can get your date corrected like this:
NSDate * dateGMT = [NSDate date];
NSTimeInterval secondsFromGMT = [[NSTimeZone localTimeZone] secondsFromGMT];
NSDate * correctDate = [dateGMT dateByAddingTimeInterval:secondsFromGMT];
-(NSDate *)getDateInCurrentSystemTimeZone
{
NSDate* sourceDate = [NSDate date];
NSTimeZone* sourceTimeZone = [NSTimeZone timeZoneWithAbbreviation:#"GMT"];
NSTimeZone* destinationTimeZone = [NSTimeZone systemTimeZone];
NSInteger sourceGMTOffset = [sourceTimeZone secondsFromGMTForDate:sourceDate];
NSInteger destinationGMTOffset = [destinationTimeZone secondsFromGMTForDate:sourceDate];
NSTimeInterval interval = destinationGMTOffset - sourceGMTOffset;
NSDate* destinationDate = [[NSDate alloc] initWithTimeInterval:interval sinceDate:sourceDate];
return destinationDate;
}
Related
I am stuck somewhere in NSDate and NSDateFormatter due to timezone issues.
I need to send time to server only in UTC(which is converted to unix time).
Here is my few steps what I am doing:
Selecting a date from the calender should be added with the current time and converted to UTC.
Compare the selected date with the current date. Just to know whether selected date is a past or future date. (Few other operations are to be done based on past/future/current date).
I have tried this code:
In a Category on NSDate :
-(NSDate *) toLocalTime{
NSDate* sourceDate = self;
NSTimeZone* sourceTimeZone = [NSTimeZone timeZoneWithName:#"UTC"];
NSTimeZone* destinationTimeZone = [NSTimeZone systemTimeZone];
NSInteger sourceGMTOffset = [sourceTimeZone secondsFromGMTForDate:sourceDate];
NSInteger destinationGMTOffset = [destinationTimeZone secondsFromGMTForDate:sourceDate];
NSTimeInterval interval = destinationGMTOffset - sourceGMTOffset;
NSDate* destinationDate = [[NSDate alloc] initWithTimeInterval:interval sinceDate:sourceDate];
return destinationDate;
}
But the problem exists when I try to convert date to local, (at times I am not sure the current time is in local timezone or not). If they are in UTC then the above method works fine.
If the time is already in local timezone then it again adds the interval and I am getting incorrect time.
I am out of ideas, please help me.
Any idea will be highly appreciated.
NSDate represents the time since Jan 1st 1970 in UTC. Never try to pretend it is anything else. Never try to think of an NSDate as being in a particular local time.
So what you need is a date from a calendar + an offset which represents the time since midnight today.
To get today 0:00am UTC, you first need a Gregorian calendar for the UTC time zone.
NSTimeZone* utcTimeZone = [NSTimeZone timeZoneWithName:#"UTC"];
NSCalendar* gregorian = [[NSCalendar alloc] initWithCalendarIdentifier: NSGregorianCalendar];
[gregorian setTimeZone: utcTimeZone];
Now you use date components to get the hours, minutes and seconds since midnight UTC
NSUInteger unitFlags = NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit;
NSDate *date = [NSDate date];
NSDateComponents *comps = [gregorian components: unitFlags fromDate:date];
If you have a date that is midnight UTC on the date from your calendar, you can get midnight UTC + your hours, minutes and seconds like this:
NSDate* theDateIWant = [gregorian dateByAddingComponents: comps
toDate: midnightUTCDateFromCalendar
options: 0];
NSLog(#"The final date is %#", theDateIWant);
I found the codes to calculate days difference between two dates here.
I write a method :
-(NSInteger)daysWithinEraFromDate:(NSDate *) startDate toDate:(NSDate *) endDate
{
NSCalendar *gregorian = [[NSCalendar alloc]
initWithCalendarIdentifier:NSGregorianCalendar];
NSInteger startDay=[gregorian ordinalityOfUnit:NSDayCalendarUnit
inUnit: NSEraCalendarUnit forDate:startDate];
NSInteger endDay=[gregorian ordinalityOfUnit:NSDayCalendarUnit
inUnit: NSEraCalendarUnit forDate:endDate];
return endDay-startDay;
}
This method has a problem: it can't consider the timezone thing. Even I add a line like this:
[gregorian setTimeZone:[NSTimeZone localTimeZone]];
My test code is like this:
NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
[dateFormat setDateFormat:#"yyyy-MM-dd HH:mm:ss"];
NSString *strDate = #"2012-09-03 23:00:00";
NSDate *dateStart = [dateFormat dateFromString:strDate];
strDate = #"2012-09-04 01:00:00";
NSDate *dateEnd = [dateFormat dateFromString:strDate];
NSLog(#"Days difference between %# and %# is: %d days",[dateFormat stringFromDate:dateStart],[dateFormat stringFromDate:dateEnd],[self daysWithinEraFromDate:dateStart toDate:dateEnd]);
The result is:
Days difference between 2012-09-03 23:00:00 and 2012-09-04 01:00:00 is: 0 days
I want to get 1 day as result by the number of midnights between the two dates. My timezone is GMT +8. But this calculation is based on GMT, so I get the wrong days number. Is there anyway to solve this problem? Thank you.
Scott Lemmon's method can solve my problem. I rewrite my code like this:
-(NSInteger)daysWithinEraFromDate:(NSDate *) startDate toDate:(NSDate *) endDate
{
NSCalendar *gregorian = [[NSCalendar alloc]
initWithCalendarIdentifier:NSGregorianCalendar];
[gregorian setTimeZone:[NSTimeZone localTimeZone]];
NSDate *newDate1 = [startDate dateByAddingTimeInterval:[[NSTimeZone localTimeZone] secondsFromGMT]];
NSDate *newDate2 = [endDate dateByAddingTimeInterval:[[NSTimeZone localTimeZone] secondsFromGMT]];
NSInteger startDay=[gregorian ordinalityOfUnit:NSDayCalendarUnit
inUnit: NSEraCalendarUnit forDate:newDate1];
NSInteger endDay=[gregorian ordinalityOfUnit:NSDayCalendarUnit
inUnit: NSEraCalendarUnit forDate:newDate2];
return endDay-startDay;
}
If the time zone offset isn't working, how about just add or subtract it manually instead?
In your case NSDate *newDate = [oldDate dateByAddingTimeInterval:(-8 * 60 * 60)]; to subtract off your +8 hours.
Or if you want to find the GMT offset automatically as well then it would simply be NSDate *newDate = [oldDate dateByAddingTimeInterval:(-[[NSTimeZone localTimeZone] secondsFromGMT])
Another thought:
A perhaps easier solution would be to just disregard the time information altogether. Just set it to the same arbitrary number for both dates, then as long as the dates come from the same timezone you will always get the correct number of mid-nights between them, regardless of GMT offset.
What you really want is the NSDate method timeIntervalSinceDate:, and take that result and if it's more than 0 but less than 86400 (the number of seconds in a day), that's one day. Otherwise, divide your result by 86400 and you'll get the number of days.
The way you currently have your code, there's only 2 hours between the two days and that's why you are seeing a result of 0 and not one.
Edit - and to determine if midnight has happened, let's try this function I just wrote off the top of my head:
- (NSDate *) getMidnightDateFromDate: (NSDate *) originalDate
{
NSDateComponents *components = [[NSCalendar currentCalendar] components:NSIntegerMax fromDate:originalDate];
[components setHour:0];
[components setMinute:0];
[components setSecond:0];
NSDate *midnight = [[NSCalendar currentCalendar] dateFromComponents:components];
return(midnight);
}
- (BOOL) howManyDaysDifferenceBetween: startDate and: endDate
{
NSDate * firstMidnight = [self getMidnightDateFromDate: startDate];
NSDate * secondMidnight = [self getMidnightDateFromDate: endDate];
NSTimeInterval timeBetween = [firstMidnight timeIntervalSinceDate: secondMidnight];
NSInteger numberOfDays = (timeBetween / 86400);
return(numberOfDays);
}
which I'm basing off Dave Delong's answer to this question. No guarantees that my code will work (I didn't test it), but I think the concept is sound.
I need to display the current Date and Time.
I have used ;
NSDate *currentDateNTime = [NSDate date];
I want to have the current date and time (Should display the system time and not GMT time).
The output should be in a NSDate format and not NSString.
for example;
NSDate *currentDateNTime = [NSDate date];
// Do the processing....
NSDate *nowDateAndTime = .....; // Output should be a NSDate and not a NSString
Since all NSDate is GMT referred, you probably want this:
(don'f forget that the nowDate won't be the actual current system date-time, but it's "shifted", so if you will generate NSString using NSDateFormatter, you will see a wrong date)
NSDate* currentDate = [NSDate date];
NSTimeZone* currentTimeZone = [NSTimeZone timeZoneWithAbbreviation:#"GMT"];
NSTimeZone* nowTimeZone = [NSTimeZone systemTimeZone];
NSInteger currentGMTOffset = [currentTimeZone secondsFromGMTForDate:currentDate];
NSInteger nowGMTOffset = [nowTimeZone secondsFromGMTForDate:currentDate];
NSTimeInterval interval = nowGMTOffset - currentGMTOffset;
NSDate* nowDate = [[NSDate alloc] initWithTimeInterval:interval sinceDate:currentDate];
Every moment in time is the same moment in time everywhere around the world —- it is just expressed as different clock times in different timezones. Therefore, you can't change the date to some other date that represents the time in your timezone; you must use an NSDateFormatter that you feed with the timezone you are in. The resulting string is the moment in time expressed in the clock time of your position.
Do all needed calculations in GMT, and just use a formatter for displaying.
Worth reading
Does [NSDate date] return the local date and time?
Some useful resources for anyone coming to this more recently:
Apple date and time programming guide do read it if you're doing anything serious with dates and times.
https://developer.apple.com/library/content/documentation/Cocoa/Conceptual/DatesAndTimes/DatesAndTimes.html#//apple_ref/doc/uid/10000039i?language=objc
Useful category on NSDate with lots of utilities does allow a ~new~ date to be generated based on an existing date.
https://github.com/erica/NSDate-Extensions
There's also a swift version of the category
https://github.com/erica/SwiftDates
You need an NSDateFormatter and call stringFromDate this method to get a string of your date.
NSDateFormatter *dateformater = [[NSDateFormatter alloc] init];
[dateformater setDateFormat:#"yyyyMMdd,HH:mm"];
NSString *str = [dateformater stringFromDate: currentDateNTime];
use this method
-(NSDate *)convertDateToDate:(NSDate *) date
{
NSDateFormatter *formatter = [[[NSDateFormatter alloc] init] autorelease];
NSDate *nowDate = [[[NSDate alloc] init] autorelease];
[formatter setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0]];
[formatter setDateFormat:#"yyyy-MM-d H:m:s"];
NSString * strdate = [formatter stringFromDate:date];
nowDate = [formatter dateFromString:strdate];
return nowDate;
}
this may return you what you want.
i hope you this may help you.
I am using NSDate to get current time and date but it is giving date and time based on GMT.Please can anyone know how to get local time?
Thanks in advance!
NSDate has no knowledge of timezones. It always stores dates as absolute moments in time, in GMT.
Use NSDateFormatter to get a local (or any other time zone) representation.
See the pertinent programming guide: http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/DataFormatting/Articles/dfDateFormatting10_4.html
[dateFormatter setTimeZone:systemTimeZone];
set the timezone of the date using a date formatter with the above method. It will work. Convert the date to string, set the format and timezone and convert back to date.
Hi I found this from another site
NSDate* sourceDate = [NSDate date];
NSTimeZone* sourceTimeZone = [NSTimeZone timeZoneWithAbbreviation:#"GMT"];
NSTimeZone* destinationTimeZone = [NSTimeZone systemTimeZone];
NSInteger sourceGMTOffset = [sourceTimeZone secondsFromGMTForDate:sourceDate];
NSInteger destinationGMTOffset = [destinationTimeZone secondsFromGMTForDate:sourceDate];
NSTimeInterval interval = destinationGMTOffset - sourceGMTOffset;
NSDate* destinationDate = [[[NSDate alloc] initWithTimeInterval:interval sinceDate:sourceDate] autorelease];
Link for the website is here
How can I get timestamp as NSNumber? I only need something like this: 1232885280
NSTimeInterval timeStamp = [[NSDate date] timeIntervalSince1970];
// NSTimeInterval is defined as double
NSNumber *timeStampObj = [NSNumber numberWithDouble: timeStamp];
Time Intervals Since 1970
NSTimeInterval timeStamp = [[NSDate date] timeIntervalSince1970];
Time Intervals Since Now
NSTimeInterval timeStamp = [[NSDate date] timeIntervalSinceNow];
Time Intervals Since Date
NSDateComponents* comps = [[NSDateComponents alloc]init];
comps.year = 2014;
comps.month = 3;
comps.day = 31;
NSCalendar* calendar = [NSCalendar currentCalendar];
NSDate* date = [calendar dateFromComponents:comps];
NSTimeInterval timeStamp = [[NSDate date] timeIntervalSinceDate:date];
Time Intervals Since Reference Date
The Intervals between the date object and 00:00:00 UTC on 1 january 2001.
NSTimeInterval timeStamp = [[NSDate date] timeIntervalSinceReferenceDate];