iOS开发---计算两个日期的时间差

    NSCalendar *calendar = [NSCalendarcurrentCalendar];

    

    unsignedint unitFlags =NSCalendarUnitYear | NSCalendarUnitMonth |NSCalendarUnitDay | NSCalendarUnitHour |NSCalendarUnitMinute | NSCalendarUnitSecond;

    

    NSDateComponents *day = [calendar components:unitFlags fromDate:startDatetoDate:endDate options:0];

    

    int sec = [day hour]*3600+[day minute]*60+[day second];

    NSLog(@"%d",sec);

    if ([day hour] ==0) {

        _numberDay = [[NSStringalloc] initWithFormat:@"%d天",[dayday]];

    }else{

        _numberDay = [[NSStringalloc] initWithFormat:@"%d天%d小时",[dayday],[day hour]];

    }