计算两个Calendar类参数相差的天数

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初学Android，遇到这个问题还不知道怎么办，Android没有提供函数来计算，而且自己数据库用的是MySQL，也是自己不熟悉的数据库，就没有过多的想用SQL来写。

在网上找了几个，感觉有些复杂，想了想有一点思路，写出来可以实现

思路：

首先判断是否日期一前一后
边计数边增加比较早的日期
等到两个日期一样时，停止操作，返回计数

/** * Created by Harry on 2015/4/27. * This class is used for compute days between two different dates */public class DateCompute {    private static String TAG = DateCompute.class.getName();    private static Calendar startDate;    private static Calendar endDate;    private static int dayCount;    public DateCompute(Calendar p_startDate, Calendar p_endDate) {        startDate = p_startDate;        endDate = p_endDate;        dayCount = 0;    }    /**     * Since both are Calendar, there is no need to add one more month each.     * @return     */    public int computeCalendar(){        /*if startDate is before endDate, loop continues*/        while(startDate.before(endDate)){            startDate.add(Calendar.DAY_OF_MONTH, 1);            dayCount++;        }        Log.v(TAG, "$$$$$$ days between two dates are : " + dayCount);        return dayCount;    }}

注意：

Calendar类中，MONTH是比真实日期小1的，所以传递参数的时候注意变换
如果遇到String类型的，要先转换成Calendar，下面的代码可以实现

这里我自己定义的字符串日期格式为：yyyy-MM-dd

方法也就是取substring，然后分别赋值给Calendar对象（数据全是数据库里提取的数据，数据库函数就没有贴上了）

    private static void calendarMinus(){        Calendar calendar1 = Calendar.getInstance();        Calendar calendar2 = Calendar.getInstance();        String sql = "select startDate, endDate from habit where userID = 2 and habitID = 2;";        Cursor cursor = Database.getDatabase().getWritableDatabase().rawQuery(sql, null);        String start, end;        cursor.moveToFirst();        start = cursor.getString(cursor.getColumnIndex("startDate"));        end = cursor.getString(cursor.getColumnIndex("endDate"));        /*yyyy-MM-dd*/        calendar1.set(Calendar.YEAR, Integer.parseInt(start.substring(0,4)));        calendar1.set(Calendar.MONTH, Integer.parseInt(start.substring(5,7)));        calendar1.set(Calendar.DAY_OF_MONTH, Integer.parseInt(start.substring(8,10)));        calendar2.set(Calendar.YEAR, Integer.parseInt(end.substring(0,4)));        calendar2.set(Calendar.MONTH, Integer.parseInt(end.substring(5,7)));        calendar2.set(Calendar.DAY_OF_MONTH, Integer.parseInt(end.substring(8,10)));        DateCompute compute = new DateCompute(calendar1, calendar2);        compute.computeCalendar();    }

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