【转载】iOS 计算某个时间点与现在的时间差

/*处理返回应该显示的时间*/
+ (NSString *) returnUploadTime:(NSDictionary *)dic
{
    //Tue May 21 10:56:45 +0800 2013
    NSString *timeStr = [dic objectForKey:@"created_at"];
    
    NSDateFormatter *date=[[NSDateFormatter alloc] init];
    [date setDateFormat:@"E MMM d HH:mm:SS Z y"];
    NSDate *d=[date dateFromString:timeStr];
    
    NSTimeInterval late=[d timeIntervalSince1970]*1;
    
    
    NSDate* dat = [NSDate dateWithTimeIntervalSinceNow:0];
    NSTimeInterval now=[dat timeIntervalSince1970]*1;
    NSString *timeString=@"";
    
    NSTimeInterval cha=now-late;
    
    if (cha/3600<1) {
        timeString = [NSString stringWithFormat:@"%f", cha/60];
        timeString = [timeString substringToIndex:timeString.length-7];
        timeString=[NSString stringWithFormat:@"%@分钟前", timeString];
        
    }
    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];
        NSDateFormatter *dateformatter=[[NSDateFormatter alloc] init];
        [dateformatter setDateFormat:@"HH:mm"];
        timeString = [NSString stringWithFormat:@"今天 %@",[dateformatter stringFromDate:d]];
        [dateformatter release];
    }
    if (cha/86400>1)
    {
//        timeString = [NSString stringWithFormat:@"%f", cha/86400];
//        timeString = [timeString substringToIndex:timeString.length-7];
//        timeString=[NSString stringWithFormat:@"%@天前", timeString];
        NSDateFormatter *dateformatter=[[NSDateFormatter alloc] init];
        [dateformatter setDateFormat:@"YY-MM-dd HH:mm"];
        timeString = [NSString stringWithFormat:@"%@",[dateformatter stringFromDate:d]];
        [dateformatter release];
    }
    [date release];
    return timeString;
}