Java 日历日期月份设置不正确

Question

我创建了一个日历，用户可以滚动浏览上个月和下个月的日历，但我遇到的问题是当用户尝试滚动到上个月时。

当用户第一次运行应用程序时单击上个月时，它可以工作，但是当用户再次单击时，它不会否认我发送到 Calendar.Set() 的值是 100% 正确的，甚至还对其进行了调试日历不会更新，因此会返回与当前月份相同的月份！

下面是我的代码。

@Override
public void onClick(View v) {

    // get current month

    int currentMonth = mCurrentMonth.get(Calendar.MONTH);
    Log.d(TAG, "day = " + mCurrentMonth.get(Calendar.DAY_OF_MONTH));

    Log.d(TAG, "currentMonth in onClick = " + currentMonth);
    if (v == mPreviousMonthButton) {
        Log.d(TAG, "mPreviousMonthButton CLICKED ");

        // if current month is january
        // decrement the current year and set month to december

        if (currentMonth == Calendar.JANUARY) {
            int currentYear = mCurrentMonth.get(Calendar.YEAR);
            mCurrentMonth.set(Calendar.YEAR, currentYear - 1);
            mCurrentMonth.set(Calendar.MONTH, Calendar.DECEMBER);
        } else {

            // else decrement the month

            Log.d(TAG, "currentMonth-- = " + currentMonth);
            mCurrentMonth.set(Calendar.MONTH, currentMonth);
            Log.d(TAG,
                    "month in previus button = "
                            + mCurrentMonth.get(Calendar.MONTH));

        }
        // save the month

        setDateForMonth();

    } else if (v == mNextMonthButton) {
        Log.d(TAG, "mNextMonthButton CLICKED ");

        if (currentMonth == Calendar.DECEMBER) {
            int currentYear = mCurrentMonth.get(Calendar.YEAR);
            mCurrentMonth.set(Calendar.YEAR, currentYear + 1);
            mCurrentMonth.set(Calendar.MONTH, Calendar.JANUARY);
        } else {
                                currentMonth--;
            mCurrentMonth.set(Calendar.MONTH, currentMonth + 1);
            Log.d(TAG, "currentMonth++ = " + currentMonth + 1);
            Log.d(TAG,
                    "month in next button = "
                            + mCurrentMonth.get(Calendar.MONTH));

        }

        // save the month

        setDateForMonth();

    }

}

这是实际更新 UI 的代码。问题出在 onClick 的某个地方，因为它在下面的代码中返回了错误的月份：

private void setDateForMonth() {

    monthList.clear();

    Log.d(TAG, ".........setDateForMonth...........");
    Log.d(TAG, "....................");

    Log.d(TAG, "month = " + mCurrentMonth.get(Calendar.MONTH));
    Log.d(TAG, "year = " + mCurrentMonth.get(Calendar.YEAR));

    CalendarMonth[] months = CalendarUtils
            .constructMonthViewArray(mCurrentMonth);

    for (int i = 0; i < months.length; i++) {
        monthList.add(months[i]);
        Log.d(TAG, monthList.get(i).getDay());
    }
    Log.d(TAG, "....................");

    mAdapter = new CalendarMonthAdapter(mContext, monthList);
    mMonthGridView.setAdapter(mAdapter);
    Months[] month = Months.values();

    String currentMonth = month[mCurrentMonth.get(Calendar.MONTH)]
            .toString();
    String year = Integer.toString(mCurrentMonth.get(Calendar.YEAR));
    mMonthLabel.setText(currentMonth + " " + year);

}

私人枚举月份 { 一月， 二月、三月、四月、五月、六月、 七月、八月、九月、十月、 十一月、十二月}；

Answer 1

除非我遗漏了一些东西，否则你实际上永远不会减少月份，除非月份是一月。

int currentMonth = mCurrentMonth.get(Calendar.MONTH);
...
if (currentMonth == Calendar.JANUARY) {
    int currentYear = mCurrentMonth.get(Calendar.YEAR);
    mCurrentMonth.set(Calendar.YEAR, currentYear - 1);
    mCurrentMonth.set(Calendar.MONTH, Calendar.DECEMBER);
} 
else {
    // else decrement the month
    Log.d(TAG, "currentMonth-- = " + currentMonth);
    mCurrentMonth.set(Calendar.MONTH, currentMonth);

你有一条评论说要减少月份，甚至有一条日志评论说你应该减少月份......但没有实际的减少:)

else {
    currentMonth--;
    mCurrentMonth.set(Calendar.MONTH, currentMonth);

Answer 2

删除 java Calendar 并移至 JodaTime

Answer 3

要添加或减去一个月，请使用 mCalendar.add(Calendar.MONTH, 1); mCalendar.add(Calendar.MONTH, -1);

Answer 4

最好使用 date4J jar 而不是 Java 的 Calendar 或 Date 类。