计算时间差

- (NSString *)intervalSinceNow: (NSString *) theDate

{

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

    [date setDateFormat:@"yyyy-MM-dd HH:mm:ss"];

    NSDate * oldDate=[date dateFromString:theDate];

    NSTimeInterval temp1=[oldDate timeIntervalSince1970]*1;

    NSDate* nowDate = [NSDate dateWithTimeIntervalSinceNow:0];

    NSTimeInterval temp12=[nowDate timeIntervalSince1970];

    NSString *timeString=@"";

    NSTimeInterval cha=temp2-temp1;

    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];

    }

    if (cha/86400>1)

    {

        timeString = [NSString stringWithFormat:@"%f", cha/86400];

        timeString = [timeString substringToIndex:timeString.length-7];

        timeString=[NSString stringWithFormat:@"%@天前", timeString];

    }

    return timeString;

}