In swift, failing converting date format, but cannot use ISO8601DateFormatter - swift

Question

I fail getting 'start' value, tested many variants and formatters. For production reasons cannot use ISO8601DateFormatter.
this code is part of creating appointment on the calendar, so I need start as start date/hour of the appointment.
Above all, I need to understand why this last line of code fails after I tried to convert date:
event.startDate is my 'start' but cannot set it since fails converting date
guard let url = URL(string: "calshow:\(event.startDate.timeIntervalSinceReferenceDate)") else { return }
DispatchQueue.main.async {
UIApplication.shared.open(url, options: [:], completionHandler: nil)
}
my code:
date0
is a Date I get from API, with value 2021-07-28 00:00:00 +0000
my updated code for creating event on calendar
let dateFormatter: DateFormatter = DateFormatter()
dateFormatter.dateFormat = "dd-MM-yyyy HH:mm:ss"
let date = dateFormatter.string(from: date0)
if let startTime = hours.from,
let startDate = date.concats(startTime),
let start = self.shortTimeFormatter.date(from: startDate) {
event.startDate = start
event.addAlarm(EKAlarm(absoluteDate: start.dayBefore))
event.addAlarm(EKAlarm(absoluteDate: start.halfHourBefore))
event.endDate = start.hourAfter
}
if let endTime = hours.to,
let endDate = date.concats(endTime),
let end = self.shortTimeFormatter.date(from: endDate) {
event.endDate = end
}
concats code
func concats(_ string: String, withSeparator separator: String? = "") -> String? {
return [self, string].compactMap{ $0 }.joined(separator: separator! + " ")
}
ShortDateTimeFormatter
public class ShortDateTimeFormatter: DateFormatter {
override public init() {
super.init()
self.dateFormat = "dd/MM/yyyy HH:mm"
}
required public init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
}

Answer 1

If I understand the code you get a Date without the time portion and you want to add the time in string format "HH:mm:ss".
Calendar can do that. You don't need to convert the Date to String and back to Date.
First create a function which converts the time string to Int components
func timeComponents(from string: String) -> (Int, Int, Int)? {
let comps = string.components(separatedBy: ":")
guard comps.count == 3,
let hr = Int(comps[0]),
let mn = Int(comps[1]),
let sc = Int(comps[2])
else { return nil }
return (hr, mn, sc)
}
Then add the time to date0 with date(bySettingHour:minute:second:of:)
if let (hr, mn, sc) = timeComponents(from: "08:30:00") {
let startDate = Calendar.current.date(bySettingHour: hr, minute: mn, second: sc, of: date0)
}
Or with DateComponents
func timeComponents(from string: String) -> DateComponents? {
let comps = string.components(separatedBy: ":")
guard comps.count == 3,
let hr = Int(comps[0]),
let mn = Int(comps[1]),
let sc = Int(comps[2])
else { return nil }
return DateComponents(hour: hr, minute: mn, second: sc)
}
if let components = timeComponents(from: "08:30:00") {
let startDate = Calendar.current.date(byAdding: components, to: date0, wrappingComponents: false)
}