How to retrieve number of hours past midnight from an NSDate object?

Question

I need to retrieve the number of hours past midnight from a UIDatePicker control in an iPhone project. datePickerMode is set to UIDatePickerModeTime

Answer 1

You can do this with your NSCalendar.

First, get your date:

NSDate *date = [timePicker date];

Next, convert it into its date components:

NSDateComponents *components = [[NSCalendar currentCalendar] components:NSIntegerMax fromDate:date];

Now we'll reset the hours and minutes of the date components so that it's now pointing at midnight:

[components setHour:0];
[components setMinute:0];
[components setSecond:0];

Next, we'll turn it back in to a date:

NSDate *midnight = [[NSCalendar currentCalendar] dateFromComponents:components];

Finally, we'll ask for the hours between midnight and the date:

NSDateComponents *diff = [[NSCalendar currentCalendar] components:NSHourCalendarUnit fromDate:midnight toDate:date options:0];

NSInteger numberOfHoursPastMidnight = [diff hour];