根据时间显示相对时间

+ (NSString*)intervalSinceNow:(NSString*)theDate
{
    NSDateFormatter *date = [[NSDateFormatter alloc] init];
    [date setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
    NSDate *d = [date dateFromString:theDate];
    NSTimeInterval late = [d timeIntervalSince1970] * 1;
    NSDate *dat = [NSDate dateWithTimeIntervalSinceNow:0];
    NSTimeInterval now = [dat timeIntervalSince1970] * 1;
    NSString *timeString = @"";
    NSTimeInterval cha = now-late;
    
    //发表在一小时之内
    if(cha / 3600 < 1) {
        if(cha / 60 < 1) {
            timeString = @"1";
        } else {
            timeString = [NSString stringWithFormat:@"%f", cha/60];
            timeString = [timeString substringToIndex:timeString.length-7];
        }
        timeString = [NSString stringWithFormat:@"%@分钟前", timeString];
        
    }
    
    //在一小时以上24小以内
    else if(cha / 3600 > 1 && cha / 86400 < 1) {
        timeString = [NSString stringWithFormat:@"%f", cha/3600];
        timeString = [timeString substringToIndex:timeString.length-7];
        timeString = [NSString stringWithFormat:@"%@小时前", timeString];
    }
    
    //发表在24以上10天以内
    else if(cha/86400>1&&cha/864000<1) {
        timeString = [NSString stringWithFormat:@"%f", cha/86400];
        timeString = [timeString substringToIndex:timeString.length-7];
        timeString = [NSString stringWithFormat:@"%@天前", timeString];
    }
    
    //发表时间大于10天 显示几月-几号 eg：11-11
    else {
        //        timeString = [NSString stringWithFormat:@"%d-%"]
        NSArray*array = [theDate componentsSeparatedByString:@" "];
        //        return [array objectAtIndex:0];
        timeString = [array objectAtIndex:0];
        timeString = [timeString substringWithRange:NSMakeRange(5, [timeString length]-5)]; 
    }
    
    return timeString;
    
}