由于工作需求自己写了一个日历, 大概思路是: 通过collectionView来做, 具备上一月下一月的切换, 日历样式自定义collectionViewCell就可以.
关键代码如下:

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view from its nib.

    _currentDate = [NSDate date];
    _firstDay = [self firstWeekdayInThisMotnth:_currentDate];
    _totalDays = [self totaldaysInMonth:_currentDate];

    [self.view addSubview:self.collectionView];
}
#pragma mark - 懒加载collectiongView
- (UICollectionView *)collectionView {
    if (!_collectionView) {
        UICollectionViewFlowLayout *layout = [[UICollectionViewFlowLayout alloc] init];
        layout.minimumLineSpacing = 0;
        layout.minimumInteritemSpacing = 0;
        layout.itemSize = CGSizeMake(([UIScreen mainScreen].bounds.size.width -20) / 7, ([UIScreen mainScreen].bounds.size.width -20) / 7 * 1.6);
        layout.headerReferenceSize = CGSizeMake([UIScreen mainScreen].bounds.size.width, 165);
        layout.scrollDirection = UICollectionViewScrollDirectionVertical;
        
        _collectionView = [[UICollectionView alloc] initWithFrame:CGRectMake(0, 0, [UIScreen mainScreen].bounds.size.width, [UIScreen mainScreen].bounds.size.height) collectionViewLayout:layout];
        _collectionView.backgroundColor = [UIColor whiteColor];
        _collectionView.delegate = self;
        _collectionView.dataSource = self;
        _collectionView.contentInset = UIEdgeInsetsMake(0, 10, 0, 10);
        [_collectionView registerNib:[UINib nibWithNibName:@"CalendarCollectionViewCell" bundle:nil] forCellWithReuseIdentifier:@"CalendarCollectionViewCell"];
        // 如果有头部视图必须要先注册
        [_collectionView registerClass:[UICollectionReusableView class] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:headerViewIdentifier];
        _collectionView.alwaysBounceVertical = YES;
        _collectionView.alwaysBounceHorizontal = NO;
    }
    return _collectionView;
}
#pragma mark - UICollectionViewDatasource
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
    return _totalDays + _firstDay;
}

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
    
    HMCalendarCollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"HMCalendarCollectionViewCell" forIndexPath:indexPath];
    
    NSInteger day = indexPath.item - _firstDay;
    
    [cell setDataWithIndex:day + 1 withIndex:indexPath.item];

    NSString *dayStr = @"";
    if ((day + 1) > 9) {
        dayStr = [NSString stringWithFormat:@"%zd",(day + 1)];
    } else {
        dayStr = [NSString stringWithFormat:@"0%zd",(day + 1)];
    }
    
    return cell;
}
#pragma mark - 日期的相关处理
// 上一月
- (void)lastMonthClick {
    _currentDate = [self lastMonth:_currentDate];
    _firstDay = [self firstWeekdayInThisMotnth:_currentDate];
    _totalDays = [self totaldaysInMonth:_currentDate];
    [self.collectionView reloadData];
}
// 下一月
- (void)nextMonthClick {
    _currentDate = [self nextMonth:_currentDate];
    _firstDay = [self firstWeekdayInThisMotnth:_currentDate];
    _totalDays = [self totaldaysInMonth:_currentDate];
    [self.collectionView reloadData];
}
// 计算某月的第一天为周几
- (NSInteger)firstWeekdayInThisMotnth:(NSDate *)date{
    NSCalendar *calendar = [NSCalendar currentCalendar]; // 取得当前用户的逻辑日历(logical calendar)
    
    [calendar setFirstWeekday:2]; //  设定每月的第一天从星期几开始，比如:. 如需设定从星期日开始，则value传入1 ，如需设定从星期一开始，则value传入2 ，以此类推
    NSDateComponents *comp = [calendar components:NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay fromDate:date];
    [comp setDay:1]; // 设置为这个月的第一天
    NSDate *firstDayOfMonthDate = [calendar dateFromComponents:comp];
    NSUInteger firstWeekday = [calendar ordinalityOfUnit:NSCalendarUnitWeekday inUnit:NSCalendarUnitWeekOfMonth forDate:firstDayOfMonthDate]; // 这个月第一天在当前日历的顺序
    // 返回某个特定时间(date)其对应的小的时间单元(smaller)在大的时间单元(larger)中的顺序
    return firstWeekday - 1;
}
// 计算某月一共有多少天
- (NSInteger)totaldaysInMonth:(NSDate *)date{
    NSRange daysInOfMonth = [[NSCalendar currentCalendar] rangeOfUnit:NSCalendarUnitDay inUnit:NSCalendarUnitMonth forDate:date]; // 返回某个特定时间(date)其对应的小的时间单元(smaller)在大的时间单元(larger)中的范围
    
    return daysInOfMonth.length;
}
// 日历的上一个月
- (NSDate *)lastMonth:(NSDate *)date{
    NSDateComponents *comp = [[NSDateComponents alloc]init];
    comp.month = -1;
    NSDate *newDate = [[NSCalendar currentCalendar] dateByAddingComponents:comp toDate:date options:0];
    return newDate;
}
// 日历的下一个月
- (NSDate *)nextMonth:(NSDate *)date{
    NSDateComponents *comp = [[NSDateComponents alloc]init];
    comp.month = 1;
    NSDate *newDate = [[NSCalendar currentCalendar] dateByAddingComponents:comp toDate:date options:0];
    return newDate;
}

#pragma mark - 日期处理方法(附加)
// 处理日期的上一日下一日
- (void)processingDateWithType:(NSInteger)type {
    // type  1为下一日    -1为上一日
    NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian];
    NSDateComponents *adComps = [[NSDateComponents alloc] init];
    [adComps setDay:type];
    _currentDate = [calendar dateByAddingComponents:adComps toDate:_currentDate options:0];
    
    self.dateLabel.text = [_currentDate stringWithDateFormatter:@"yyyy.MM.dd"];
}
// 判断是不是当天
- (BOOL)isSameDay:(NSDate*)date1 date2:(NSDate*)date2
{
    NSCalendar* calendar = [NSCalendar currentCalendar];
    
    unsigned unitFlags = NSCalendarUnitYear | NSCalendarUnitMonth |  NSCalendarUnitDay;
    NSDateComponents* comp1 = [calendar components:unitFlags fromDate:date1];
    NSDateComponents* comp2 = [calendar components:unitFlags fromDate:date2];
    
    return [comp1 day]   == [comp2 day] &&
    [comp1 month] == [comp2 month] &&
    [comp1 year]  == [comp2 year];
}