iOS 根据日期，获取该日期所在周，月，年的开始日期，结束日期 的方法

转载自 魏超的博客

- (void)getMonthBeginAndEndWith:(NSDate *)newDate{
    if (newDate == nil) {
        newDate = [NSDate date];
    }
    double interval = 0;
    NSDate *beginDate = nil;
    NSDate *endDate = nil;
    
    NSCalendar *calendar = [NSCalendar currentCalendar];
    [calendar setFirstWeekday:2];//设定周一为周首日
    BOOL ok = [calendar rangeOfUnit:NSMonthCalendarUnit startDate:&beginDate interval:&interval forDate:newDate];
    // 分别修改为 NSCalendarUnitDay NSCalendarUnitWeekOfYear NSCalendarUnitYear
    if (ok) {
        endDate = [beginDate dateByAddingTimeInterval:interval-1];
    }else {
        return;
    }
    NSDateFormatter *myDateFormatter = [[NSDateFormatter alloc] init];
    [myDateFormatter setDateFormat:@"yyyy.MM.dd"];
    NSString *beginString = [myDateFormatter stringFromDate:beginDate];
    NSString *endString = [myDateFormatter stringFromDate:endDate];

    NSString *s = [NSString stringWithFormat:@"%@-%@",beginString,endString];
    NSLog(@"%@",s);
}