C#串口接收的数据放入到DataSet里面，却出现错误，怎么修改，求帮助

[wang4288782]

// Obtain the number of bytes waiting in the port's buffer获得的字节数放在串口的缓冲区

int bytes = comport.BytesToRead;

// Create a byte array buffer to hold the incoming data创建一个字节数组缓冲来保存传入的数据

byte[] buffer = new byte[bytes];

// Read the data from the port and store it in our buffer从串口读取数据并将其存储在缓冲中

comport.Read(buffer, 0, bytes);
for (int i = 0; i < buffer.Length; i++)
{
buf.Add(buffer[i]);
}
MemoryStream str = new MemoryStream(buf.ToArray());
DataSet.ReadXml(str);这里出现错误，说给定编码中的字符无效。

怎么修改，求帮助

[愚知]

str 要转码！
string Newstr = System.TEXT.Encoding.utf8.getstring(str)