why i get an error in the date formatter code? - ios

Question

I’m trying to convert my AM PM time pickers to 24h format to print the start and end time to calculate the price but i got an unknown error. attached is photo of my UI to simplify the idea and my code.
Note: the end time is automatically shows after i choose the start time
#objc func donePressed(){
// formatter
let formatter = DateFormatter()
formatter.dateStyle = .none
formatter.timeStyle = .short
startTimeTxt.text = formatter.string(from: StartTimePicker.date)
self.view.endEditing(true)
endTimeTxt.text = formatter.string(from: EndTimePicker.date)
self.view.endEditing(true)
let starttimecal = StartTimeTxt.text!
let endtimecal = EndTimeTxt.text!
let StartTo24 = starttimecal
let EndTo24 = endtimecal
let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "h:mm a"
let sTime = dateFormatter.date(from: startTo24)
dateFormatter.dateFormat = "HH:mm"
let sTime24 = dateFormatter.string(from: sTime!)
print("24 hour formatted Date:", sTime24)
let eTime = dateFormatter.date(from: endTo24)
dateFormatter.dateFormat = "HH:mm"
let eTime24 = dateFormatter.string(from: eTime!) // here the fatal error comes after i choose the start time from simulator
print("24 hour formatted Date:", eTime24)
}

Answer 1

To get the 12h time format to display in the text fields you can use the formatter you already have but I also like to set the locale
let dateFormatter12h = DateFormatter()
dateFormatter12h.locale = Locale(identifier: "en_US_POSIX")
dateFormatter12h.dateFormat = "h:mm a"
To calculate the time difference there is a function for that in the Calendar class, here we calculate the number of hours and minutes between two dates (this is an assumption since I don't know exactly what calculation you want to do)
let hourAndMinutes = Calendar.current.dateComponents([.hour, .minute], from: startDate, to: endDate)
Below is a more complete example
//Sample data
let startDate = Date()
let endDate = startDate.addingTimeInterval(3.25*60*60) //add 3h and 15 minutes
// Format and print in 12h format
let dateFormatter12h = DateFormatter()
dateFormatter12h.locale = Locale(identifier: "en_US_POSIX")
dateFormatter12h.dateFormat = "h:mm a"
let start = dateFormatter12h.string(from: startDate)
let end = dateFormatter12h.string(from: endDate)
print(start, end)
// Calculate time difference in hours and minutes
let hourAndMinutes = Calendar.current.dateComponents([.hour, .minute], from: startDate, to: endDate)
print(hourAndMinutes)
// Calculate price, the formula is just an example
let price = hourAndMinutes.hour! * 15 + hourAndMinutes.minute! * 15 / 60
print(price)
Output
6:46 PM 10:01 PM
hour: 3 minute: 15 isLeapMonth: false
48