NSDate 总结

最近做一个限时抢购，根据当前时间判断当前活动的状态，最好是用服务器返回的时间，因为本地时间用户可以更改，中间去掉“T”是因为服务器返回的 2016-12-13T12:00:00

   NSDate *currentDate = [NSDate date];NSDateFormatter *formatter = [[NSDateFormatter alloc] init];formatter.locale = [NSLocale localeWithLocaleIdentifier:@"en_US"];formatter.dateFormat = @"yyyy-MM-dd HH:mm:ss";NSString * beginString=[self.GetBeginAt stringByReplacingOccurrencesOfString:@"T" withString:@" "];NSDate *beginDate=[formatter dateFromString:beginString];NSString * endString =[self.GetEndAt stringByReplacingOccurrencesOfString:@"T" withString:@" "];NSDate *endDate=[formatter dateFromString:endString];if ([self isBetweenFromdate:beginDate todate:endDate]) {//在这个时间段就是：拼抢中}else if([currentDate compare:endDate]==NSOrderedDescending) {//比这个时间段大：已结束}else {//比这个时间段小：即将开始}

- (BOOL)isBetweenFromdate:(NSDate *)dateFrom todate:(NSDate *)dateTo {NSDate *currentDate = [NSDate date];if ([currentDate compare:dateFrom]==NSOrderedDescending && [currentDate compare:dateTo]==NSOrderedAscending) {//比开始时间大，比结束时间小return YES;}return NO;
}

// 判断是否是同一天
+ (BOOL)isSameDay:(NSString *)dateStr1 date2:(NSString *)dateStr2
{NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];[dateFormatter setDateFormat:@"yyyy-MM-dd"];NSDate *date1 = [dateFormatter dateFromString:dateStr1];NSDate *date2 = [dateFormatter dateFromString:dateStr2];NSCalendar *calendar = [NSCalendar currentCalendar];unsigned unitFlag = NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit;NSDateComponents *comp1 = [calendar components:unitFlag fromDate:date1];NSDateComponents *comp2 = [calendar components:unitFlag fromDate:date2];return (([comp1 day] == [comp2 day]) && ([comp1 month] == [comp2 month]) && ([comp1 year] == [comp2 year]));
}

+(NSTimeInterval)getSecondsFrom:(NSString *)fDate to:(NSString *)tDate
{NSDateFormatter *dateFormatter=[[NSDateFormatter alloc] init];[dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];NSDate *date1=[dateFormatter dateFromString:fDate];NSDate *date2=[dateFormatter dateFromString:tDate];//这里的NSTimeInterval 并不是对象，是基本型，其实是double类型，是由c定义的:typedef double NSTimeInterval;NSTimeInterval time=[date2 timeIntervalSinceDate:date1];return time;
}

 NSDateFormatter *formater = [[NSDateFormatter alloc] init];formater.dateFormat = @"yyyy-MM-dd hh:mm:ss";NSDate *Date = [formater dateFromString:date];NSDate *currentDate = [NSDate date];double tempTimeInterval = [Date timeIntervalSinceDate:currentDate];int day=3600*24;int temp=tempTimeInterval/day;if(temp<= 7 && temp>=0){self.overdueImage.hidden=NO;}else{self.overdueImage.hidden=YES;}

+ (NSDate *)getNowDateFromatAnDate:(NSDate *)anyDate
{//设置源日期时区NSTimeZone* sourceTimeZone = [NSTimeZone timeZoneWithAbbreviation:@"UTC"];//或GMT//设置转换后的目标日期时区NSTimeZone* destinationTimeZone = [NSTimeZone localTimeZone];//得到源日期与世界标准时间的偏移量NSInteger sourceGMTOffset = [sourceTimeZone secondsFromGMTForDate:anyDate];//目标日期与本地时区的偏移量NSInteger destinationGMTOffset = [destinationTimeZone secondsFromGMTForDate:anyDate];//得到时间偏移量的差值NSTimeInterval interval = destinationGMTOffset - sourceGMTOffset;//转为现在时间NSDate* destinationDateNow = [[NSDate alloc] initWithTimeInterval:interval sinceDate:anyDate];return destinationDateNow;
}

dateFromString  为 nil

通常情况是 dateformat  设置的原因，

 formater.dateFormat = @"yyyy-MM-dd HH:mm:ss";

formater.dateFormat = @"yyyy-MM-dd hh:mm:ss";