(Obj-c) Identify morning, afternoon or night from a date string - ios

Question

I'm working in Objective-C. I have this three values in string, which they determine the part of the day
NSString *morning = #"7:01";
NSString *afternoon = #"12:01"
NSString *night = #"19:01"
And my original date is this, also in String
NSString *currentTime = #"Sat, 17 Oct 2015 9:58 am CDT"
I need to identify if the current date is morning, afternoon or night according with the current date as String. Anyone have a solution?

Answer 1

Your question has received a negative score (-4 at the time of writing) as people obviously feel you haven't shown the effort SO expects. However your question hides a gotcha and something which Apple recently made harder, which makes it interesting.
Your sample time is:
NSString *currentTime = #"Sat, 17 Oct 2015 9:58 am CDT"
which would seem to be "morning". However this is exactly the same time as:
Sat, 17 Oct 2015 2:58 pm GMT
which would seem to be "afternoon". Both these times are:
Sat, 17 Oct 2015 14:58 UTC
Why is this an issue?
An NSDate is a point in time without any associated time zone. The class NSDateFormatter, and associated methods on NSDate itself, will parse a date-time string and produce the absolute UTC point in time the string represents. Any time zone in the string, such as CDT in the example, is allowed for in determining the absolute time point but is not directly represented in the NSDate value that results.
When the NSCalendar class is used to break out the parts of a date it does so in relation to a time zone, which defaults to the system time zone.
What all this adds up to is if your app is running, say, on a computer in the UK and you follow the suggestion in the comments:
parse the time (using NSDateFormatter)
break out the hour & min to get an NSDateComponents value (using NSCalendar); and
compare the hour & min to your boundaries then your sample time will be reported as "afternoon"
Not good :-(
What you need is to parse the date-time (getting a standard UTC time point) and the time zone, you can then pass that time zone to NSCalendar and the rest is easy.
Apple makes it harder
Prior to OS X 10.9 & iOS 7 the NSDateFormatter class returned an NSCalendarDate date value, that type was a subclass of NSDate and also stored an NSTimeZone value. So parsing your sample returned both the time point "Sat, 17 Oct 2015 14:58 UTC" and the time zone "UTC-5". With that information NSCalendar could be used to break out the hour & min and correctly determine the time is "morning".
NSCalendarDate is now deprecated, and while it is still possible to use it this could change at any moment. Apple do not yet appear to have provide an alternative "parse date and time zone" method.
Parsing both the date and time zone offset
From the simple observation that if you parse "Sat, 17 Oct 2015 9:58 am CDT" ignoring the time zone and treating it as UTC the result is an absolute time point which differs by 5 hours, the time zone offset for CDT, from the one obtained if the string is parsed taking the time zone into account you have a method to obtain the time zone - parse the string twice, once ignoring the time zone, and determine the difference.
This may not be the best algorithm, but it does work... (you may insert here warnings about premature optimisation!)
So here goes (minimal comments, look the methods up in the documentation, error checking etc. - treat as an outline only):
- (BOOL) dateAndZoneFromString:(NSString *)timeString // the date-time string
dateFormat:(NSString *)dateFormat // the format of the date-time, should contain a time zone format at the end
parsedDate:(NSDate **)date // NSDate representing the absolute time point
parsedZone:(NSTimeZone **)zone // NSTimeZone representing the time zone of the original string
error:(NSError **)error
{
NSDateFormatter *df = [NSDateFormatter new];
// parse timeString taking time zone into account
df.dateFormat = dateFormat;
NSDate *absDate = [df dateFromString:timeString];
// parse timeString ignoring the time zone by removing the format specifier from dateFormat
df.timeZone = [NSTimeZone timeZoneWithAbbreviation:#"UTC"];
df.dateFormat = [dateFormat stringByReplacingOccurrencesOfString:#" *[zZvV]+$" withString:#"" options:NSRegularExpressionSearch range:NSMakeRange(0, dateFormat.length)];
NSDate *zonelessDate;
NSRange range = NSMakeRange(0, timeString.length);
if ( [df getObjectValue:&zonelessDate forString:timeString range:&range error:error] )
{
// parse successful, calculate the difference and construct an NSTimeZone value
NSTimeInterval offset = [zonelessDate timeIntervalSinceDate:absDate];
NSTimeZone *timezone = [NSTimeZone timeZoneForSecondsFromGMT:offset];
*date = absDate;
*zone = timezone;
return YES;
}
else
return NO;
}
If you pass #"Sat, 17 Oct 2015 9:58 am CDT" and for format #"E, d MMM y h:m a z" to this method it will return the time point "Sat, 17 Oct 2015 14:58 UTC" as an NSDate and the time zone "UTC-5" as an NSTimeZone.
If you pass #"Sat, 17 Oct 2015 2:58 pm GMT" then it will return the same absolute time point and a time zone of "UTC+0".
For this point you can use these values with NSCalendar, NSDateComponents, and simple comparisons to determine morning/afternoon/night.
HTH

Answer 2

-(void)ShowTimeMessage
{
// For calculating the current date
NSDate *date = [NSDate date];
// Make Date Formatter
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:#"hh a EEEE"];
// hh for hour mm for minutes and a will show you AM or PM
NSString *str = [dateFormatter stringFromDate:date];
// NSLog(#"%#", str);
// Sperate str by space i.e. you will get time and AM/PM at index 0 and 1 respectively
NSArray *array = [str componentsSeparatedByString:#" "];
// Now you can check it by 12. If < 12 means Its morning > 12 means its evening or night
NSString *message;
NSString *timeInHour;
NSString *am_pm;
NSString *DayOfWeek;
if (array.count>2)
{
// am pm case
timeInHour = array[0];
am_pm = array[1];
DayOfWeek = array[2];
}
else if (array.count>1)
{
// 24 hours case
timeInHour = array[0];
DayOfWeek = array[1];
}
if (am_pm)
{
if ([timeInHour integerValue]>=4 && [timeInHour integerValue]<=9 && [am_pm isEqualToString:#"AM"])
{
message = [NSString stringWithFormat:#"Morning"];
}
else if (([timeInHour integerValue]>=10 && [timeInHour integerValue]!=12 && [am_pm isEqualToString:#"AM"]) || (([timeInHour integerValue]<4 || [timeInHour integerValue]==12) && [am_pm isEqualToString:#"PM"]))
{
message = [NSString stringWithFormat:#"Afternoon"];
}
else if ([timeInHour integerValue]>=4 && [timeInHour integerValue]<=9 && [am_pm isEqualToString:#"PM"])
{
message = [NSString stringWithFormat:#"Evening"];
}
else if (([timeInHour integerValue]>=10 && [timeInHour integerValue]!=12 && [am_pm isEqualToString:#"PM"]) || (([timeInHour integerValue]<4 || [timeInHour integerValue]==12) && [am_pm isEqualToString:#"AM"]))
{
message = [NSString stringWithFormat:#"Night"];
}
}
else
{
if ([timeInHour integerValue]>=4 && [timeInHour integerValue]<10)
{
message = [NSString stringWithFormat:#"Morning"];
}
else if ([timeInHour integerValue]>=10 && [timeInHour integerValue]<16)
{
message = [NSString stringWithFormat:#"Afternoon"];
}
else if ([timeInHour integerValue]>=16 && [timeInHour integerValue]<22)
{
message = [NSString stringWithFormat:#"Evening"];
}
else
{
message = [NSString stringWithFormat:#"Night"];
}
}
if (DayOfWeek)
{
_timeLbl.text=[NSString stringWithFormat:#"%# %#",DayOfWeek,message];
}
}