I have got two timevalues in the format: %H%M%S (E.G.161500)
These values are text-based integers.
Is there a simple function in Cocoa that calculates the difference between these two integers using a 60 seconds and minutes scale?
So if
time 1 = 161500
time 2 = 171500
timedifference = 003000
NSDateFormatter *dateFormatter = [[[NSDateFormatter alloc] init] autorelease];
[dateFormatter setDateFormat:#"HHmmss"];
NSDate *date1 = [dateFormatter dateFromString:#"161500"];
NSDate *date2 = [dateFormatter dateFromString:#"171500"];
NSTimeInterval diff = [date2 timeIntervalSinceDate:date1]; // diff = 3600.0
The class for manipulating dates is NSDate. The method for getting time intervals is -timeIntervalSinceDate:. The result is a NSTimeInterval value, which is a double representing the interval in seconds.
You can create a NSDate object from a NSString with +dateWithString:, provided that your date is formatted as 2001-03-24 10:45:32 +0600.
try this code.
- (NSTimeInterval)intervalBetweenDate:(NSDate *)dt1 andDate:(NSDate *)dt2 {
NSTimeInterval interval = [dt2 timeIntervalSinceDate:dt1];
NSLog(#"%f",interval);
return interval;
}
I would create an NSFormatter subclass to parse time values in that format from input data (you can put one on a text field to automatically convert user input, or use it to parse from a data source in code). Have it return the combined number of seconds as an NSTimeInterval (double representing seconds) wrapped in an NSNumber. From there it's easy to subtract the difference, and display it using the same NSFormatter class you created. In both parsing and displaying values, you're the one responsible to write code converting from seconds to hours:minutes:seconds or whatever format you like. You could also convert these values to an NSDate like mouviciel mentioned, if it makes sense for your application. Just keep in mind you're always going to be storing the time difference from a reference date, usually Jan 1st 1970 (NSDate has methods to do this for you).
Related
See sample code as follows - unable to use custom time here. Why is this not possible giving a result:
NSDate *dt1 = [NSDate date]; //2018-07-26 08:31:22 +0000
NSString *datestr = [NSString stringWithFormat:#"%#", [NSDate date]];//2018-07-26 10:42:09 +0001
NSString *cutstring = 09:00 PM;
I would just create date with NSDateComponents where you can set year, month, hour, minute etc. Refer https://nshipster.com/nsdatecomponents/
Extracting Components From Dates
NSDateComponents can be initialized and manipulated manually, but most often, they’re extracted from a specified date, using NSCalendar -components:fromDate::
Swift
Objective-C
let calendar = NSCalendar.currentCalendar()
let date = NSDate()
let components = calendar.components([.Month, .Day], fromDate: date)
The components parameter is a bitmask of the date component values to retrieve, with many to choose from:
Swift
Objective-C
NSCalendarUnit.Era
NSCalendarUnit.Year
NSCalendarUnit.Month
NSCalendarUnit.Day
NSCalendarUnit.Hour
NSCalendarUnit.Minute
NSCalendarUnit.Second
NSCalendarUnit.Weekday
NSCalendarUnit.WeekdayOrdinal
NSCalendarUnit.Quarter
NSCalendarUnit.WeekOfMonth
NSCalendarUnit.WeekOfYear
NSCalendarUnit.YearForWeekOfYear
NSCalendarUnit.Calendar
NSCalendarUnit.TimeZone
Since it would be expensive to compute all of the possible values, specify only the components that will be used in subsequent calculations (joining with |, the bitwise OR operator).
I am getting the following string from a server in my iOS app:
20140621-061250
How can I convert it to the local time?
How can I define my date formatter? Is this correct?
dateFormatter.dateFormat = #"YYYYMMd-HHmmss";
The question doesn't specify the nature of what you mean by converting, exactly, but the first thing you should do, regardless of the final goal, is to correctly parse the server response using a properly configured NSDateFormatter. This requires specification of the correct format string, and the time zone must be explicitly set on the formatter or it will infer it from the local time, which would be incorrect in most cases.
Specify The Format String
Let's look at the input string provided:
20140621-061250
This uses four digits for the year, two digits (with a zero-padding) for the month, and two digits (presumably, these will be zero-padded as well) for the day. This is followed by a -, then two digits to represent the hour, 2 digits for the minute, and 2 digits for the second.
Referring to the Unicode date format standards, we can derive the format string in the following way. The four digits representing the calendar year will be replaced with yyyy in the format string. Use MM for the month, and dd for the day. Next would come the literal -. For the hours, I assume that it will be in 24 hour format as otherwise this response is ambiguous, so we use HH. Minutes are then mm and seconds ss. Concatenating the format specifiers yields the following format string, which we will use in the next step:
yyyyMMdd-HHmmss
In our program, this would look like:
NSString *dateFormat = #"yyyyMMdd-HHmmss";
Configure the input date formatter
The time format above does not specify a time zone, but because you have been provided the specification for the server response that it represents the UTC time, we can code this into our application. So, we instantiate an NSDateFormatter, set the correct time zone, and set the date format:
NSTimeZone *inputTimeZone = [NSTimeZone timeZoneWithAbbreviation:#"UTC"];
NSDateFormatter *inputDateFormatter = [[NSDateFormatter alloc] init];
[inputDateFormatter setTimeZone:inputTimeZone];
[inputDateFormatter setDateFormat:dateFormat];
Convert the input string to an NSDate
For demonstration purposes, we hard-code the string you received from the server response; you would replace this definition of inputString with the one you get from the server:
NSString *inputString = #"20140621-061250";
NSDate *date = [inputDateFormatter dateFromString:inputString];
At this point, we have the necessary object to do any further conversions or calculations - an NSDate which represents the time communicated by the server. Remember, an NSDate is just a time stamp - it has no relation to a time zone whatsoever, which only plays a role when converting to and from string representations of the date, or representations of a calendrical date via NSDateComponents.
Next steps
The question doesn't clearly specify what type of conversion is needed, so we'll see an example of formatting the date to display in the same format as the server response (although, I can't think of a likely use case for this particular bit of code, to be honest). The steps are quite similar - we specify a format string, a time zone, configure a date formatter, and then generate a string (in the specified format) from the date:
NSTimeZone *outputTimeZone = [NSTimeZone localTimeZone];
NSDateFormatter *outputDateFormatter = [[NSDateFormatter alloc] init];
[outputDateFormatter setTimeZone:outputTimeZone];
[outputDateFormatter setDateFormat:dateFormat];
NSString *outputString = [outputDateFormatter stringFromDate:date];
Since I'm in UTC-06:00, printing outputString gives the following:
20140621-001250
It's likely you'll instead want to use setDateStyle: and setTimeStyle: instead of a format string if you're displaying this date to the user, or use an NSCalendar to get an NSDateComponents instance to do arithmetic or calculations on the date. An example for displaying a verbose date string to the user:
NSTimeZone *outputTimeZone = [NSTimeZone localTimeZone];
NSDateFormatter *outputDateFormatter = [[NSDateFormatter alloc] init];
[outputDateFormatter setTimeZone:outputTimeZone];
[outputDateFormatter setDateStyle:NSDateFormatterFullStyle];
[outputDateFormatter setTimeStyle:NSDateFormatterFullStyle];
NSString *outputString = [outputDateFormatter stringFromDate:date];
Printing outputString here gives us the following:
Saturday, June 21, 2014 at 12:12:50 AM Mountain Daylight Time
Note that setting the time zone appropriately will handle transitions over daylight savings time. Changing the input string to "20141121-061250" with the formatter style code above gives us the following date to display (Note that Mountain Standard Time is UTC-7):
Thursday, November 20, 2014 at 11:12:50 PM Mountain Standard Time
Summary
Any time you get date input in a string form representing a calendar date and time, your first step is to convert it using an NSDateFormatter configured for the input's format, time zone, and possibly locale and calendar, depending on the source of the input and your requirements. This will yield an NSDate which is an unambiguous representation of a moment in time. Following the creation of that NSDate, one can format it, style it, or convert it to date components as needed for your application requirements.
To get your string into a NSDate, you would use a NSDateFormatter like this:
NSString *myDateAsAStringValue = #"20140621-061250"
NSDateFormatter *df = [[NSDateFormatter alloc] init];
[df setDateFormat:#"yyyyMMdd-HHmmss"];
NSDate *myDate = [df dateFromString: myDateAsAStringValue];
You may want to read this post about working with Date and Time
EDIT:
To parse it as UTC you have to add the line:
[df setTimeZone:[NSTimeZone timeZoneWithAbbreviation:#"UTC"]];
Also, when you print it with NSLog, if you are using the same NSDateFormatter, you will get the input string as output (since you apply the inverse of the parsing function).
Here is the full code, for parsing and for getting the output with a standard format:
//The input
NSString *myDateAsAStringValue = #"20140621-061250";
//create the formatter for parsing
NSDateFormatter *df = [[NSDateFormatter alloc] init];
[df setTimeZone:[NSTimeZone timeZoneWithAbbreviation:#"UTC"]];
[df setDateFormat:#"yyyyMMdd-HHmmss"];
//parsing the string and converting it to NSDate
NSDate *myDate = [df dateFromString: myDateAsAStringValue];
//create the formatter for the output
NSDateFormatter *out_df = [[NSDateFormatter alloc] init];
[out_df setDateFormat:#"yyyy-MM-dd'T'HH:mm:ssz"];
//output the date
NSLog(#"the date is %#",[out_df stringFromDate:myDate]);
One possible solution in Swift using NSDate extension (maybe it could help future viewers of this question):
import UIKit
// For your personal information: NSDate() initializer
// always returns a date in UTC, no matter the time zone specified.
extension NSDate {
// Convert UTC (or GMT) to local time
func toLocalTime() -> NSDate {
let timezone: NSTimeZone = NSTimeZone.localTimeZone()
let seconds: NSTimeInterval = NSTimeInterval(timezone.secondsFromGMTForDate(self))
return NSDate(timeInterval: seconds, sinceDate: self)
}
// Convert local time to UTC (or GMT)
func toGlobalTime() -> NSDate {
let timezone: NSTimeZone = NSTimeZone.localTimeZone()
let seconds: NSTimeInterval = -NSTimeInterval(timezone.secondsFromGMTForDate(self))
return NSDate(timeInterval: seconds, sinceDate: self)
}
}
I'm trying to make a label to show the temperature, with a maximum of 3 digits for temperatures over a 100, but I don't want any decimals...
NSString *longtempstring = [tmp description];
NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
[formatter setMaximumFractionDigits:3];
[formatter setMinimumFractionDigits:0];
NSString *shorttempstring = [formatter stringForObjectValue:[NSString stringWithString:longtempstring]];
The code above always returns (null)
Any ideas?
You are getting nil because the object you are passing to stringForObjectValue: is not of the type expected.
First of all, don't use stringForObjectValue:. That is a member of the parent class, NSFormatter. NSNumberFormatter has more specific methods that avoid confusion of object types like numberFromString: and stringFromNumber:.
Second, NSNumberFormatter is used to go from number to formatted string or formatted string to number. Not directly from formatted string to formatted string. You will need to use one number formatter to read your original string and produce a number and another to produce a new shorter formatted string from that number.
Of course, you might be able to make the first step (from long string to number) easier by using NSScanner or by taking a substring of your long string (cutting out everything except for the number itself) and then using the NSString method integerValue or doubleValue. A regular expression could also be used to extract the number from the first (longer) string.
The long and short of it is, this is a two step process. The first step (getting a number) can be accomplished any number of ways and a NSNumberFormatter might not be the easiest way. The second step (getting a new shorter string) is what NSNumberFormatter is perfect for.
I fixed it by converting the NSString to an NSNumber and only pulling the integer value from the string, thus removing any decimals.
NSString *longtempstring = [tmp description];
NSNumber *tempintegervalue = [NSNumber numberWithInteger:[longtempstring integerValue]];
NSString *shorttempstring = [tempintegervalue stringValue];
NSString *longtempstring = [tmp description];
What is the value of longtempstring here? Is it even a number?
NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
[formatter setMaximumFractionDigits:3];
[formatter setMinimumFractionDigits:0];
Why do you set maximum fraction digits to 3 if you say that you don't want any fraction digits? Fraction digits are what is "after the dot" and you say you don't want any decimals. If you don't want any decimals, minimum and maximum must be set to 0.
NSString *shorttempstring = [formatter stringForObjectValue:[NSString stringWithString:longtempstring]];
First of all, why are you copying the string? [NSString stringWithString:...] creates a new string that is a copy of the string you provide as argument. Strings are immutable, there is no need to copy them, they won't be modified. If you are afraid that a NSString may in fact be a NSMutableString, after all that is a subclass of NSString and you want to copy it, just copy it by calling [aString copy]. copy is a very smart method here. If the NSString is in fact a mutable string, it will really copy it, so you get an immutable copy. If it is not a mutable string, though, copy just returns the same string with a retain count increased by one (so in that case copy behaves exactly like retain). However, in your case copying makes no sense whatsoever.
And second, what makes you believe, that you can feed a string into a NSNumberFormater? It is called NSNumberFormater because it formats objects of type NSNumber. How is a NSString a NSNumber? It is not called NSStringFormater. If you feed an object of the wrong class to a formater, it will return nil, that's how this method is documented.
If your longtempstring contains a number with fraction, e.g. 12.345, then the correct code would look like this:
NSString * longtempstring = [tmp description];
NSNumberFormatter * formatter = [[NSNumberFormatter alloc] init];
[formatter setMaximumFractionDigits:0];
[formatter setMinimumFractionDigits:0];
NSNumber * tempnumber = [NSNumber numberWithDouble:[longtempstring doubleValue]];
NSString * shorttempstring = [formatter stringForObjectValue:tempnumber];
However, if all you want to do is cut off the decimals, that is a horrible way to do it. This can be done much more effective:
double d;
NSString * longtempstring;
NSString * shorttempstring;
longtempstring = #"12.345";
d = [longtempstring doubleValue];
shorttempstring = [NSString stringWithFormat:#"%d", (int)d];
This is much shorter, needs less memory, and is at least three times faster. If you want to round the number (that means everything with a fraction .5 and above is rounded to the next higher value), just round it:
d = round([longtempstring doubleValue]);
I want to assign nstimeInterval value to nsdate.
NSDate *startTime=[NSDate date] ;
NSDate *endTime=[NSDate date] ;
NSTimeInterval difference=[endTime
timeIntervalSinceDate:startTime];
startTime=difference; This gives me an error.
how can i assign my difference result of nsTimeInterval type to nsdate?
thanks in Advance
You need to understand that NSTimeInterval is the difference between two dates. What you're trying to do is like telling the program to:
Set the date to 2 days.
When what you want to do is tell the program to:
Set the date to last monday plus 2 days.
Therefore you need to use one of these family of NSDate methods:
+ dateWithTimeIntervalSinceNow:
+ dateWithTimeInterval:sinceDate:
+ dateWithTimeIntervalSinceReferenceDate:
+ dateWithTimeIntervalSince1970:
– initWithTimeIntervalSinceNow:
– initWithTimeInterval:sinceDate:
– initWithTimeIntervalSinceReferenceDate:
– initWithTimeIntervalSince1970:
Where you create the NSDate with some reference date plus/minus the NSTimeInterval; note that NSDate objects are immutable so there are no methods to change the date represented by the object using NSTimeInterval values.
See the NSDate Class Reference for more details.
To correct your code, this is how you'd do it:
NSDate *startTime=[NSDate date] ;
NSDate *endTime=[NSDate date] ;
NSTimeInterval difference=[endTime timeIntervalSinceDate:startTime];
NSDate *newTime = [NSDate dateWithTimeInterval:difference sinceDate:startDate];
I am storing the date and time in strings using NSUserDefaults when an action is performed. next time the app is run, I want to check the time since the last date and time, and display a message if this is greater than a specified time period.
Is this possible?
In viewDidLoad I retrieve the NSUserDefaults with the saved date and time, and I get the current date, but how do i compare them, and 'do something' if the time difference is bigger than specified?
Use NSDate's timeIntervalSinceDate: method.
By the way, you can store NSDates directly in NSUserDefaults. You don't need to convert them to/from strings.
You could do something like that:
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
NSDate * lastUpdate = [defaults valueForKey:#"mysettingdate"];
if(!lastUpdate){
lastUpdate = [NSDate dateWithTimeIntervalSince1970:0];
}
NSDate *localDate = [NSDate date];
NSTimeInterval timeZoneOffset = [[NSTimeZone defaultTimeZone] secondsFromGMT];
NSTimeInterval gmtTimeInterval = [localDate timeIntervalSinceReferenceDate] + timeZoneOffset;
NSDate *gmtDate = [NSDate dateWithTimeIntervalSinceReferenceDate:gmtTimeInterval];
NSDateComponents *diff = [[NSCalendar currentCalendar] components:NSMinuteCalendarUnit fromDate:lastUpdate toDate:gmtDate options:0];
NSLog(#"diff in minutes:%d", [diff minute]); //or hour, days, seconds
if ([diff minute]>0) {
//do your stuff :)
}