iOS计算时间差

iOS 计算现在时间与所截取时间点的时间差

//计算上报时间差          NSDateFormatter *formatter = [[NSDateFormatter alloc] init];          [formatter setDateFormat:@"YYYY-MM-dd HH:mm:ss"];//设置你想要的格式,hh与HH的区别:分别表示12小时制,24小时制          NSTimeZone* timeZone = [NSTimeZone timeZoneWithName:@"Asia/Beijing"];          [formatter setTimeZone:timeZone];          NSDate *datenow = [NSDate date];          //设置一个字符串的时间          NSMutableString *datestring = [NSMutableString stringWithFormat:@"%@",20141202052740];          //注意 如果20141202052740必须是数字，如果是UNIX时间，不需要下面的插入字符串。          [datestring insertString:@"-" atIndex:4];          [datestring insertString:@"-" atIndex:7];          [datestring insertString:@" " atIndex:10];          [datestring insertString:@":" atIndex:13];          [datestring insertString:@":" atIndex:16];          NSLog(@"datestring==%@",datestring);          NSDateFormatter * dm = [[NSDateFormatter alloc]init];          //指定输出的格式   这里格式必须是和上面定义字符串的格式相同，否则输出空          [dm setDateFormat:@"YYYY-MM-dd HH:mm:ss"];          NSDate * newdate = [dm dateFromString:datestring];          long dd = (long)[datenow timeIntervalSince1970] - [newdate timeIntervalSince1970];          NSString *timeString=@"";          if (dd/3600<1)          {              timeString = [NSString stringWithFormat:@"%ld", dd/60];              timeString=[NSString stringWithFormat:@"%@分钟前", timeString];          }          if (dd/3600>1&&dd/86400<1)          {              timeString = [NSString stringWithFormat:@"%ld", dd/3600];              timeString=[NSString stringWithFormat:@"%@小时前", timeString];          }          if (dd/86400>1)          {              timeString = [NSString stringWithFormat:@"%ld", dd/86400];              timeString=[NSString stringWithFormat:@"%@天前", timeString];          }          NSLog(@"=====%@",timeString);