最近项目需要，需要在winform中模拟表单将数据提交至服务器，发现单独提交键值对很容易实现，单独实现上传文件也很容易实现。要是同时提交键值对和文件，比较麻烦。在百度谷歌了大半天没有任何收获。无奈之下，按照 黑月.Net的 的思路去自己写。经过奋斗 终于搞定。
方法如下：

public WebResponse SubmitData(string fileName, Uri uri, string[] keys, string[] values)
{
string boundary = "----------" + DateTime.Now.Ticks.ToString("x");
HttpWebRequest httpWebRequest2 = (HttpWebRequest)WebRequest.Create(uri);
//httpWebRequest2.Credentials = credentialCache;//
httpWebRequest2.ContentType = "multipart/form-data; boundary=" + boundary;
httpWebRequest2.Method = "POST";

// Build up the post message header

StringBuilder sb = new StringBuilder();

if (keys != null)
{
for (int i = 0; i < keys.Length; i++)
{
sb.Append("--");
sb.Append(boundary);
sb.Append("\r\n");
sb.Append("Content-Disposition: form-data; name=\"" + keys[i] + "\"\r\n\r\n");
sb.Append(values[i]);
sb.Append("\r\n");
}
}

sb.Append("--");
sb.Append(boundary);
sb.Append("\r\n");
sb.Append("Content-Disposition: form-data; name=\"file\"; filename=\"");
sb.Append(Path.GetFileName(fileName));
sb.Append("\"");
sb.Append("\r\n");
sb.Append("Content-Type: application/octet-stream");
sb.Append("\r\n");
sb.Append("\r\n");

string postHeader = sb.ToString();
byte[] postHeaderBytes = Encoding.UTF8.GetBytes(postHeader);

// Build the trailing boundary string as a byte array
// ensuring the boundary appears on a line by itself
byte[] boundaryBytes = Encoding.ASCII.GetBytes("\r\n--" + boundary + "\r\n");

FileStream fileStream = new FileStream(fileName, FileMode.Open, FileAccess.Read);
long length = postHeaderBytes.Length + fileStream.Length + boundaryBytes.Length;
httpWebRequest2.ContentLength = length;

Stream requestStream = httpWebRequest2.GetRequestStream();

// Write out our post header
requestStream.Write(postHeaderBytes, 0, postHeaderBytes.Length);

// Write out the file contents
byte[] buffer = new Byte[checked((uint)Math.Min(4096, (int)fileStream.Length))];
int bytesRead = 0;
while ((bytesRead = fileStream.Read(buffer, 0, buffer.Length)) != 0)
requestStream.Write(buffer, 0, bytesRead);

// Write out the trailing boundary
requestStream.Write(boundaryBytes, 0, boundaryBytes.Length);

WebResponse webResponse2 = httpWebRequest2.GetResponse();
return webResponse2;

}