java - 谁能解释为什么 4 个日历中有 1 个显示 Time=？

Question

我有 4 个日历:startCal、endCal、reminderCal 和 Today。今天只是获取当前日期/时间的 Calendar.getInstance()，而其他 3 个则使用 Android 日期/时间选择器通过相同的方法选择日期和时间。

startCal 和 endCal 工作正常 if(startCal.after(endCal)){//处理错误 }

但是，reminderCal.before(today) 不会返回 true，即使我故意在当前日期之前设置reminderCal。

此外，在打印所有时间时，reminerCal 没有任何时间 (Time=?) 并且 areFieldsSet=false，但是如果我第二次提交，时间就会更新，尽管 before() 方法仍然没有更新不工作!

除了 else if (reminderCal.before(today)) 之外，一切似乎都有效

public boolean validInput(){
    if(startCal.after(endCal)){
        //THIS WORKS
        timeError.setText(getString(R.string.error_event_end_early));
        isOk = false;
        Log.e(TAG, "validInput: Event ends before it starts");
    }

    if(hasReminder.isChecked()){
        if(reminderDate.getText().toString().matches("")) {
            // THIS WORKS
            reminderError.setText(R.string.error_no_reminder);
            isOk = false;
            Log.e(TAG, "validInput: No reminder set");
        } else if (reminderCal.before(today)){
            // THIS DOESN'T WORK. Why?
            reminderError.setText(R.string.error_reminder_early);
            isOk = false;
            Log.e(TAG, "validInput: Reminder too early " + reminderCal.toString());
        }  else if(reminderCal.after(startCal)){
            //THIS WORKS
            reminderError.setText(R.string.error_reminder_late);
            isOk = false;
            Log.e(TAG, "validInput: Reminder too late");
        }
    return isOk;
}


    Log.e(TAG, "Debugging: \n" +
            "strCalandar: " + startCal.toString() + "\n" +
            "endCalandar: " + endCal.toString() + "\n" +
            "remCalandar: " + reminderCal.toString() + "\n" +
            "todCalandar: " + today.toString() + "\n");
}

今天 = Calander.getInstance();无需进一步调整。其他日历从这些方法获取日期/时间。

public void showDatePickerDialog(final EditText text, final Calendar cal){
    Log.d(TAG, "showDatePickerDialog: Open");
    DialogFragment datePicker = new DatePickerFragment();
    ((DatePickerFragment) datePicker).setOnDateChosenListener(new DatePickerFragment.OnDateChosenListener() {
        @Override
        public void onDateChosen(int year, int month, int day) {
            text.setText(String.format("%02d/%02d/%04d", day, month, year));
            cal.set(year, month, day);
        }
    });
    datePicker.show(getSupportFragmentManager(), "DatePicker");
}

public void showTimePickerDialog(final EditText text, final Calendar cal){
    Log.d(TAG, "showTimePickerDialog: Open");
    DialogFragment timePicker = new TimePickerFragment();
    ((TimePickerFragment) timePicker).setOnTimeChosenListener(new TimePickerFragment.OnTimeChosenListener() {
        @Override
        public void onTimeChosen(int hour, int min) {
            text.setText(String.format("%02d:%02d", hour, min));
            cal.set(Calendar.HOUR_OF_DAY, hour);
            cal.set(Calendar.MINUTE, min);
        }
    });
    timePicker.show(getSupportFragmentManager(), "TimePicker");
}

Logcat 中的输出:

strCalandar: java.util.GregorianCalendar[time=1566152201478,areFieldsSet=true,areAllFieldsSet=true,lenient=true,zone=libcore.util.ZoneInfo[id="Europe/London",mRawOffset=0,mEarliestRawOffset=0,mUseDst=true,mDstSavings=3600000,transitions=242],firstDayOfWeek=2,minimalDaysInFirstWeek=4,ERA=1,YEAR=2019,MONTH=7,WEEK_OF_YEAR=33,WEEK_OF_MONTH=3,DAY_OF_MONTH=18,DAY_OF_YEAR=230,DAY_OF_WEEK=1,DAY_OF_WEEK_IN_MONTH=3,AM_PM=1,HOUR=7,HOUR_OF_DAY=19,MINUTE=16,SECOND=41,MILLISECOND=478,ZONE_OFFSET=0,DST_OFFSET=3600000]
endCalandar: java.util.GregorianCalendar[time=1566152201478,areFieldsSet=true,areAllFieldsSet=true,lenient=true,zone=libcore.util.ZoneInfo[id="Europe/London",mRawOffset=0,mEarliestRawOffset=0,mUseDst=true,mDstSavings=3600000,transitions=242],firstDayOfWeek=2,minimalDaysInFirstWeek=4,ERA=1,YEAR=2019,MONTH=7,WEEK_OF_YEAR=33,WEEK_OF_MONTH=3,DAY_OF_MONTH=18,DAY_OF_YEAR=230,DAY_OF_WEEK=1,DAY_OF_WEEK_IN_MONTH=3,AM_PM=1,HOUR=7,HOUR_OF_DAY=19,MINUTE=16,SECOND=41,MILLISECOND=478,ZONE_OFFSET=0,DST_OFFSET=3600000]
remCalandar: java.util.GregorianCalendar[time=?,areFieldsSet=false,areAllFieldsSet=false,lenient=true,zone=libcore.util.ZoneInfo[id="Europe/London",mRawOffset=0,mEarliestRawOffset=0,mUseDst=true,mDstSavings=3600000,transitions=242],firstDayOfWeek=2,minimalDaysInFirstWeek=4,ERA=1,YEAR=2019,MONTH=7,WEEK_OF_YEAR=31,WEEK_OF_MONTH=1,DAY_OF_MONTH=2,DAY_OF_YEAR=214,DAY_OF_WEEK=6,DAY_OF_WEEK_IN_MONTH=1,AM_PM=1,HOUR=5,HOUR_OF_DAY=17,MINUTE=18,SECOND=41,MILLISECOND=478,ZONE_OFFSET=0,DST_OFFSET=3600000]
todCalandar: java.util.GregorianCalendar[time=1562775401478,areFieldsSet=true,areAllFieldsSet=true,lenient=true,zone=libcore.util.ZoneInfo[id="Europe/London",mRawOffset=0,mEarliestRawOffset=0,mUseDst=true,mDstSavings=3600000,transitions=242],firstDayOfWeek=2,minimalDaysInFirstWeek=4,ERA=1,YEAR=2019,MONTH=6,WEEK_OF_YEAR=28,WEEK_OF_MONTH=2,DAY_OF_MONTH=10,DAY_OF_YEAR=191,DAY_OF_WEEK=4,DAY_OF_WEEK_IN_MONTH=2,AM_PM=1,HOUR=5,HOUR_OF_DAY=17,MINUTE=16,SECOND=41,MILLISECOND=478,ZONE_OFFSET=0,DST_OFFSET=3600000]

如果提醒日期设置在当前日期之前，reminderCal.before(today) 应返回 true

Answer 1

他们试图在文档的这一部分中解释它:

set(f, value) changes calendar field f to value. In addition, it sets an internal member variable to indicate that calendar field f has been changed. Although calendar field f is changed immediately, the calendar's time value in milliseconds is not recomputed until the next call to get(), getTime(), getTimeInMillis(), add(), or roll() is made. Thus, multiple calls to set() do not trigger multiple, unnecessary computations. As a result of changing a calendar field using set(), other calendar fields may also change, depending on the calendar field, the calendar field value, and the calendar system. In addition, get(f) will not necessarily return value set by the call to the set method after the calendar fields have been recomputed. The specifics are determined by the concrete calendar class.

Example: Consider a GregorianCalendar originally set to August 31, 1999. Calling set(Calendar.MONTH, Calendar.SEPTEMBER) sets the date to September 31, 1999. This is a temporary internal representation that resolves to October 1, 1999 if getTime()is then called. However, a call to set(Calendar.DAY_OF_MONTH, 30) before the call to getTime() sets the date to September 30, 1999, since no recomputation occurs after set() itself.

因此，由于您调用 cal.set(Calendar.HOUR_OF_DAY, hour); 和 cal.set(Calendar.MINUTE, min);，时间暂时未定义，这就是为什么从 toString 打印问号的原因。

我无法重现之前和之后的报告行为，但似乎可以合理地假设它们在之前也无法正常工作get 或调用其中提到的 getXxx 方法之一。

这只是Calendar 类设计中非常令人困惑的方面之一。好的解决方案是改用 java.time, the modern Java date and time API .