objctive-c获取当年当月第一天和最后一天

有时候查询数据记录需要不按照日期，按照月份怎么办，有时候年份为平年，闰年等等，这里有个通用的办法。

- (NSArray *)getMonthFirstAndLastDayWith:(NSString *)dateStr{

    

    NSDateFormatter *format=[[NSDateFormatter alloc] init];

    [format setDateFormat:@"yyyy-MM-dd"];

    NSDate *newDate=[format dateFromString:dateStr];

    double interval = 0;

    NSDate *firstDate = nil;

    NSDate *lastDate = nil;

    NSCalendar *calendar = [NSCalendar currentCalendar];

    

    BOOL OK = [calendar rangeOfUnit:NSCalendarUnitMonth startDate:& firstDate interval:&interval forDate:newDate];

    

    if (OK) {

        lastDate = [firstDate dateByAddingTimeInterval:interval - 1];

    }else {

        return @[@"",@""];

    }

    

    NSDateFormatter *myDateFormatter = [[NSDateFormatter alloc] init];

    [myDateFormatter setDateFormat:@"yyyy-MM-dd"];

    NSString *firstString = [myDateFormatter stringFromDate: firstDate];

    NSString *lastString = [myDateFormatter stringFromDate: lastDate];

    return @[firstString, lastString];

}