I have design an application in which i am have three text field in which i am giving my time like as 10:10 PM. Now problem is that i want to calculate time difference between current time and entered time. How calculate time?
Depending what you mean by "entered time" you will most likely need to look at NSDateFormatter and parse the entered time into a usable form, then get a date using NSDate (i.e. NSDate * now = [NSDate date];) and do whatever math you need using the methods available in `NSDate'.
If you are just determining the difference between entered date and now this method would suit you:
- (NSTimeInterval)timeIntervalSinceNow
you can get the difference in seconds using time intervals (e.g. that of the NSDate and CFAbsoluteTimeGetCurrent).
Related
I know you guys might be saying that this question is very common but actually I'm referring to the actual current date and time:
Let say today is 1st of August,12pm and no matter how the user change their phone date and time, I will still know today is 1st of August, 12pm...
Anyone know how can I do that?
You can get the real date and time from an NTP server, but this assumes that you have internet access.
If the user changes their phone date and time, then you will get that date and time... since NSDate gets its value from the iOS. If you want it to return the actual time per time zone, you will have to set up a small Web Service or something that returns the time for that particular time zone.
NSDate *currentDate = [NSDate date];
Now currentDate will have the current date & time when this code is executed.
I would like to make a function that input a NSDate and output the last date of the month. Do you guys know how to do it in Cocoa?
It's the day before the first day of the next month. Add a month, set the day to 1, subtract a day. For setting the day to 1, you'll find it easier to go via NSCalendar. See here for details.
If you're doing date computations, you should always use NSCalendar and related classes, because that's the only way to be forward-compatible with changes to calendars, support for non-"standard" calendars, and so on.
Read the Date and Time Programming Guide section on Calendrical Calculations to get an idea of how these classes work together.
I need a function which receives [NSDate date] and a string #"2010-11-12" and returns the amount of days between those two dates.
More explanation:
I need to store a date from a server in the format #"2010-11-12" in my NSUserdefaults. The meaning of this date is the expireDate of a feature in an iPhone App. Every time I press on a button for this feature I need to check if the difference in days between the current time->[NSDate date] and #"2010-11-12" is greater than 0. That means that the feature is disabled.
It's making me crazy, maybe it's dead simple.
Use an NSDateFormatter to convert the string to an NSDate - then compare the date objects.
I'm trying to figure out how to calculate store opening times based on the way they are normally expressed. For example: Monday - Friday, 9am - 6pm. I want to know two things from this criteria. Is the store open? If it is how long will it be before it closes?
My confusion with the documentation is that NSDate calculations expect unique date data sets to perform calculations not generic as expressed above. For example NSDate expects 2010-07-12T09:00:00Z & 2010-07-12T18:00:00Z to form the start basis of the calculation and like wise for the days in between.
Do I need to create a data set for the year on this basis to calculate the results? Or is there a clever way I can get NSCalendar / NSDateComponents to do all this hard work for me?
There is no simple/automatic way. You have to parse the string yourself, form two, let's say startDate and endDate (or something alike). From them you can extract the day of the week and time (that's where NSCalendar and NSDateComponents come in handy).
I just want to clarify if I am understanding how dates & time zones work.
Basically, I have a date string #"2008-07-06 12:08:49" that I want to convert to an NSDate. I want this date and time to be in whatever the current user's time zone is set in. So if they are in GMT or HST, it's still 12:08:49.
If I have date in unix form 1215382129 (UTC) and my time zone is set to London (GMT), the outputted date from NSLog() is:
2008-07-06 12:08:49 +0100
If I then change my time zone to Hawaii (HST) and output the same date, I get:
2008-07-06 12:08:49 -1000
This seems to work fine, but I was under the impression to get the time in Hawaiian, I'd have to physically add the time difference (-10hrs) to the unix time stamp. Is this not required then?
Does that mean, whatever date and time a unix time is pointing to, it always points to the same date and time in whatever time zone a user is in?
Hope this makes sense!
Edit
I've just realised (thanks to Kevin Conner!) that in fact NSDateFormatter is creating different unix timestamps for that date string depending on the current timezone! So I was totally wrong!! :-)
Disclaimer, I'm mostly a Java guy. But Cocoa seems to work like the Java library in this regard: Dates are zoneless timestamps. Time zones are in the domain of formatting dates for display. In other words, the internal format doesn't consider time zones, it's all in UTC. Time zones are relatively a convenience for humans, so they are in the display/parsing side.
I noticed there is a setTimeZone: method on NSDateFormatter. Try calling that on your formatter before performing the format.