[iOS]时间筛选之<本周、上周、更早>

1、可以实现时间筛选，目测应该还有更简单的方法。

思路： 获取当天时间，和目标时间进行比对操作。

注意点：时区 时区 时区 重要的时区说三遍。

- (void)viewDidLoad {
    [super viewDidLoad];
    NSDate * today = [NSDate date];
    
    //定义当前时区时间
    NSString * time =@"2015-08-16 00:00:00";
    NSDate* xmlData = [self dateFromString:time];
    
    xmlData = [self getNowDateFromatAnDate:xmlData];
    
    if([self intervalSinceNow:xmlData]>=[self getTodayisWeek:today]+7)
    {
        NSLog(@"这个日期是很早以前");
    }
    if([self intervalSinceNow:xmlData]>=[self getTodayisWeek:today]&&[self intervalSinceNow:xmlData]<[self getTodayisWeek:today]+7)
    {
        NSLog(@"这个日期是上周");
    }
    if([self intervalSinceNow:xmlData]<7&&[self intervalSinceNow:xmlData]<[self getTodayisWeek:today])
    {
        NSLog(@"这个日期是本周");
    }
    
    
}

- (int)intervalSinceNow: (NSDate *) theDate
{
    NSTimeInterval late=[theDate timeIntervalSince1970]*1;
    
    NSDate* dat = [NSDate dateWithTimeIntervalSinceNow:0];
    dat=  [self getNowDateFromatAnDate:dat];
    NSTimeInterval now=[dat timeIntervalSince1970]*1;
    NSString *timeString=@"";
    
    NSTimeInterval cha=now-late;
    
    if (cha/86400>1)
    {
        timeString = [NSString stringWithFormat:@"%f", cha/86400];
        timeString = [timeString substringToIndex:timeString.length-7];
        return [timeString intValue];
    }
    return -1;
   
}

- (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;
}
- (NSDate *)dateFromString:(NSString *)dateString{
    
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    
    [dateFormatter setDateFormat: @"yyyy-MM-dd HH:mm:ss"];
    
     NSDate *destDate= [dateFormatter dateFromString:dateString];
    
     return destDate;
    
}

//获得某日是周几
-(int)getTodayisWeek:(NSDate *)today
{
    today = [self getNowDateFromatAnDate:today];
    NSCalendar*calendar = [NSCalendar currentCalendar];
    NSDateComponents*comps;
    [comps setWeekday:0];
    comps =[calendar components:(NSCalendarUnitWeekday)fromDate:today];
    NSInteger weekday = [comps weekday]; // 星期几（注意，周日是“1”，周一是“2”。。。。）
    int  factWeekDay;
    //默认是周日开始
    switch (weekday) {
        case 1:
            factWeekDay = 7  ;
            break;
        case 2:
            factWeekDay = 1  ;
            break;
        case 3:
            factWeekDay = 2  ;
            break;
        case 4:
            factWeekDay = 3  ;
            break;
        case 5:
            factWeekDay = 4  ;
            break;
        case 6:
            factWeekDay = 5  ;
            break;
        case 7:
            factWeekDay = 6  ;
            break;
        default:
            break;
    }
    
    return  factWeekDay;
}