Background: I was working on an Android project where concurrencies in date booking will raise, and I have used MaterialDatePicker in order to choose the dates.

Problem: I need to DISABLE some SPECIFIC dates that are already selected by other users in order to handle the concurrencies. I am able to fetch the dates selected by other users from the firestore (Firebase - backend development platform), but unable to deal with the calender. I came across a blog which suggests to use setDisabledDays(calender[] days), but not so clearly how to do that?!

Need help with! - how do I disable specific dates on the calender???

Calendar calendar = Calendar.getInstance(TimeZone.getTimeZone("UTC"));
    calendar.clear();
    long today = MaterialDatePicker.todayInUtcMilliseconds();
    calendar.setTimeInMillis(today);
    calendar.set(Calendar.MONTH, Calendar.JANUARY);
    long January = calendar.getTimeInMillis();
    calendar.set(Calendar.MONTH, Calendar.DECEMBER);
    long December = calendar.getTimeInMillis();

    CalendarConstraints.Builder calenderConstraintBuilder = new CalendarConstraints.Builder();
    calenderConstraintBuilder.setOpenAt(today);
    calenderConstraintBuilder.setValidator(DateValidatorPointForward.now());
    MaterialDatePicker.Builder builder = MaterialDatePicker.Builder.datePicker();
    builder.setTitleText("Select start date");
    builder.setCalendarConstraints(calenderConstraintBuilder.build());
    MaterialDatePicker materialDatePicker = builder.build(); 

    mDatePickerBtn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            materialDatePicker.show(getSupportFragmentManager(), "DATE_PICKER");
        }
    });

    materialDatePicker.addOnPositiveButtonClickListener(new MaterialPickerOnPositiveButtonClickListener() {
        @Override
        public void onPositiveButtonClick(Object selection) {
            duration = materialDatePicker.getHeaderText();
            //This duration variable must be stored in database, it has both start and end date
            dateResult.setText("Selected dates: " + duration);
        }
    });