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Android ZoneDateTime.withHour always sets hour to 8

So I am tring to schedule alarm at a particular time on current day using AlarmManager.
To do that I am using ZoneDateTime to get current time and then updating it to the hour at which I need to set the alarm. But for some reason time.withHour is giving me 8pm or 8am no matter what hour I am passing to it. Am I doing something wrong here?
var time = ZonedDateTime.now() //getting current time at my timezone
time = time.withHour(22).withMinute(8).withSecond(0)
print(time) //getting 8am/8pm at my timezone
val timeMilis = time.toInstant().toEpochMilli()

Android AlarmManager scheduling through time zone or daylight shifts

I have a logic that schedules reminders using AlarmManager. I need to implement the following:
Logic 1: when the user changes time zone, eg he travels from UK (UTC+0) to central Europe (UTC+1), alarms should follow the time zone.
Example, a reminder scheduled at 3PM UTC+0 should fire at 4PM UTC+1
Logic 2: when a time shift occurs, eg time shifts to daylight saving time in spring (from UTC+1 to UTC+2), alarms should keep the original time
Example, a reminder scheduled at 3PM UTC+1 should fire at 3PM UTC+2
How can I achieve this? As of now I have no particular logic in place and all the alarms follow Logic 1. I have found no way to identify when a time shift happens.
Scheduling logic is very simple:
LocalDateTime reminderTime = LocalDateTime.of(...)
ZoneOffset currentOffsetForMyZone = ZoneId.systemDefault().getRules().getOffset(Instant.now());
reminderTime.toInstant(currentOffsetForMyZone).toEpochMilli();
alarmManager.setExact(AlarmManager.RTC_WAKEUP, reminderTime, pendingIntent);

For each alarm store the time of day and the time zone in which it was set. This suffices for firing the alarm at the right time no matter if the user is currently in a different time zone. And Java will take summer time (DST) into account.
Your example times and UTC offsets correspond to standard time in those time zones, so let’s start with an example date in standard time even though it was a couple of days ago now:
LocalTime alarmTime = LocalTime.of(15, 0);
ZoneId alarmTimeZone = ZoneId.of("Europe/London");
// Travel to Paris and see the alarm go off at 4, assuming standard time
ZoneId currentTimeZone = ZoneId.of("Europe/Paris");
Instant actualAlarmTime = LocalDate.of(2021, Month.MARCH, 18)
.atTime(alarmTime)
.atZone(alarmTimeZone)
.toInstant();
ZonedDateTime timeOnLocation = actualAlarmTime.atZone(currentTimeZone);
System.out.format("Scheduled at %s or %d millis, goes off at %s local time%n",
actualAlarmTime, actualAlarmTime.toEpochMilli(), timeOnLocation);
The code prints:
Scheduled at 2021-03-18T15:00:00Z or 1616079600000 millis, goes off at
2021-03-18T16:00+01:00[Europe/Paris] local time
Let’s also try a date in the summer time part of the year. I have changed Paris to London and MARCH to APRIL:
// Stay back home in the UK
ZoneId currentTimeZone = ZoneId.of("Europe/London");
Instant actualAlarmTime = LocalDate.of(2021, Month.APRIL, 18)
.atTime(alarmTime)
.atZone(alarmTimeZone)
.toInstant();
Scheduled at 2021-04-18T14:00:00Z or 1618754400000 millis, goes off at
2021-04-18T15:00+01:00[Europe/London] local time
The basic trick is: don’t use the current offset for the time zone where you set the alarm. Let Java automatically apply the offset for the date and time where the alarm is to go off.

If anyone is interested, the fix was to apply the correct offset for the date and time where the alarm is to go of, as pointed out by Ole. My silly mistake was to apply always the current timezone.
LocalDateTime alarmTime = LocalDateTime.of(...)
ZoneId zone = ZoneId.systemDefault();
ZonedDateTime zoneDateTime = ZonedDateTime.of(alarmTime , zone);
long startAtMillis = zoneDateTime.toInstant().toEpochMilli();
//Fire alarm
notificationAlarm.setExactAndAllowWhileIdle(AlarmManager.RTC_WAKEUP, startAtMillis, pendingIntent);

android best way to set an alarm in android

i have a general question to set an alarm in android.
at the moment, the user can chose a date and time with a date picker (which is a date in the future).
then i will set the the delay time for the alarm.
I convert the chosen date & time in milliseconds and subtract System.currentTimeMillis() = this difference I set for the delay of my alarm.
my question is, if this the best way to calculate the delay or is there a better solution?
this calculation i use for update an alarm, too

Look at the Android Alarm Manager class. You can use it to set alarms at specific times, without calculating the delay.
final AlarmManager am = (AlarmManager) App.instance.getSystemService(Context.ALARM_SERVICE);
Calendar c = GregorianCalendar.getInstance();
c.set(2015, 12, 20, 10, 30);
am.set(AlarmManager.RTC_WAKEUP, c.getTimeInMillis(), operation);
where operation is a PendingIntent of the action you want to do when the alarm triggers.

My solution for you here:
You should convert normal datetime to timestemp formart
You can calculate by subtract future timestemp (which is set by alarm time) with current timestemp of phone to get return value then convert it to hour, munite and day number.
If after calculate get result is zezo then you notify alarm to user.
else nothing to do

my alarm manager calendar comparison is not getting the expected result

I made a comparison between two calendars:
Year, Month and day are the current year, month and day: but the result is not as expected if the time of the first calendar is after the current time the calendar waits till that time and starts ringing but if it's before the current time the calendar starts ringing directly so it's always accessing the second condition:
public void scheduleAlarm()
{
//to initialize the time variable not a real value:
Long time=Long.parseLong("0");
int hour=calendar.get(Calendar.HOUR);
int minute=calendar.get(Calendar.MINUTE);
Calendar cal_now = new GregorianCalendar(Year,Month,Day, hour, minute,Calendar.SECOND);
Calendar cal_alarm_first=new GregorianCalendar(Year,Month,Day,21,14,0);
//if the first calendar is in the past increment its day by one:
if(cal_alarm_first.before(cal_now)){
Notif_Body=getResources().getString(R.string.remembrance_body_first);
//here if the first alarm is already gone I should add a day and it should ring after a day from now with the specified hour and minute...
cal_alarm_first.add(Calendar.DATE, 1);
time=cal_alarm_first.getTimeInMillis();
}
else if(cal_alarm_first.after(cal_now)){
//the problem is here it always access this condition even if the first calendar time is before the current time for example same date but the first calendar is 9:14 and current time is 9:17 it always access this condition and the alarm starts ringing...
Notif_Body=getResources().getString(R.string.remembrance_body_first);
time=cal_alarm_first.getTimeInMillis();
}
//to send this alarm to be retrieved by the broadcast receiver class:
Intent intentAlarm = new Intent(this, TimeAlarm.class);
//add the notification body to the intent:
intentAlarm.putExtra("Notif_body", Notif_Body);
// create the object
AlarmManager alarmManager = (AlarmManager) getSystemService(Context.ALARM_SERVICE);
//set the alarm for particular time
alarmManager.set(AlarmManager.RTC_WAKEUP,time, PendingIntent.getBroadcast(this,1,intentAlarm, PendingIntent.FLAG_UPDATE_CURRENT));
}
I really can't figure out what the problem is!! thanks.
Edit:
so the cause of this unexpected result was because of the 24hours format I am adding the time of the first calendar in 24hours format and the current time is getting its time placed as 12 hours format so need to get both of them in 24 hours format;
Edit2:
So I changed the
int hour=calendar.get(Calendar.HOUR);//12 hours
to
int hour=calendar.get(Calendar.HOUROFDAY);//24 hours
and basically worked will add it as an answer if it really worked...

the cause of this unexpected result was because of the 24hours format I am adding the time of the first calendar in 24hours format and the current time is getting its time placed as 12 hours format so need to get both of them in 24 hours format;
So I changed the:
int hour=calendar.get(Calendar.HOUR);//12 hours
to
int hour=calendar.get(Calendar.HOUROFDAY);//24 hours
and it worked!!

PopUp Alarm on selected days and selected time in android

I want to popup an alarm on selected day i.e. Monday ,Tuesday and so on. And at selected time on every week. I've an idea about interval but I don't know how to get the next day and popup alarm ?

You need to use the AlarmManager and get a WakeClock while processing the Intent in Service (make sure to release it and chose the right kind).
Here is a great example :
https://stackoverflow.com/a/8801990/220710
To get the day current day of the week, look at this question :
Android: how to get the current day of the week (Monday, etc...) in the user's language?
Then you would use :
setInexactRepeating(int type, long triggerAtMillis, long intervalMillis, PendingIntent operation)
Schedule a repeating alarm
that has inexact trigger time requirements; for example, an alarm that
repeats every hour, but not necessarily at the top of every hour.
Then you would need to set :
type = RTC_WAKEUP
intervalMillis = ms in a week
triggerAtMillis = System.currentTimeMillis() + ms to the next Monday, Tuesday or
whatever
intent = the intent you want to fire to a Service that
will process it.