如果你需要跨域上传内容到另外一个域名并且需要获取返回值，使用Asp.Net的作为代理是最好的办法，要是客户端直接提交到iframe中，由于跨域是无法用javascript获取到iframe中返回的内容的。此时需要在自己的网站做一个动态页作为代理，将表单提交到动态页，动态页负责将表单的内容使用WebClient或HttpWebRequest将表单数据再上传到远程服务器，由于在服务器端进行操作，就不存在跨域问题了。
WebClient上传只包含键值对的文本信息示例代码：
复制代码代码如下:
string uriString = "http://localhost/login.aspx";
// 创建一个新的 WebClient 实例.
WebClient myWebClient = new WebClient();
string postData = "Username=admin&Password=admin";
// 注意这种拼字符串的ContentType
myWebClient.Headers.Add("Content-Type","application/x-www-form-urlencoded");
// 转化成二进制数组
byte[] byteArray = Encoding.ASCII.GetBytes(postData);
// 上传数据，并获取返回的二进制数据.
byte[] responseArray = myWebClient.UploadData(uriString,"POST",byteArray);
WebClient上传只包含文件的示例代码：
复制代码代码如下:
String uriString = "http://localhost/uploadFile.aspx";
// 创建一个新的 WebClient 实例.
WebClient myWebClient = new WebClient();
string fileName = @"C:/upload.txt";
// 直接上传，并获取返回的二进制数据.
byte[] responseArray = myWebClient.UploadFile(uriString,"POST",fileName);
对于既包含文件又包含文本键值对信息的示例代码，需要构造表单提交的内容，对于学asp的同学来说，下面的表单提交内容一定不会陌生
复制代码代码如下:
-----------------------------7d429871607fe
Content-Disposition: form-data; name="file1"; filename="G:/homepage.txt"
Content-Type: text/plain
武林网：http://www.vevb.com
-----------------------------7d429871607fe
Content-Disposition: form-data; name="filename"
default filename
-----------------------------7d429871607fe--
所以只要拼一个这样的byte[] data数据Post过去，就可以达到同样的效果了。但是一定要注意，对于这种带有文件上传的，其ContentType是不一样的，例如上面的这种，其ContentType为"multipart/form-data; boundary=---------------------------7d429871607fe"。有了ContentType，我们就可以知道boundary(就是上面的"---------------------------7d429871607fe")，知道boundary了我们就可以构造出我们所需要的byte[] data了，最后，不要忘记，把我们构造的ContentType传到WebClient中（例如:webClient.Headers.Add("Content-Type", ContentType);）这样，就可以通过WebClient.UploadData 方法上载文件数据了。
using System;using System.Web;using System.IO;using System.Net;using System.Text;using System.Collections;namespace UploadData.Common{ public class CreateBytes { Encoding encoding = Encoding.UTF8; public byte[] JoinBytes(ArrayList byteArrays) { int length = 0; int readLength = 0; // 加上结束边界 string endBoundary = Boundary + "-- "; byte[] endBoundaryBytes = encoding.GetBytes(endBoundary); byteArrays.Add(endBoundaryBytes); foreach (byte[] b in byteArrays) { length += b.Length; } byte[] bytes = new byte[length]; // 遍历复制 foreach (byte[] b in byteArrays) { b.CopyTo(bytes, readLength); readLength += b.Length; } return bytes; } public bool UploadData(string uploadUrl, byte[] bytes, out byte[] responseBytes) { WebClient webClient = new WebClient(); webClient.Headers.Add("Content-Type", ContentType); try { responseBytes = webClient.UploadData(uploadUrl, bytes); return true; } catch (WebException ex) { Stream resp = ex.Response.GetResponseStream(); responseBytes = new byte[ex.Response.ContentLength]; resp.Read(responseBytes, 0, responseBytes.Length); } return false; } /// 获取普通表单区域二进制数组 public byte[] CreateFieldData(string fieldName, string fieldValue) { string textTemplate = Boundary + " Content-Disposition: form-data; name="{0}" {1} "; string text = String.Format(textTemplate, fieldName, fieldValue); byte[] bytes = encoding.GetBytes(text); return bytes; } public byte[] CreateFieldData(string fieldName, string filename, string contentType, byte[] fileBytes) { string end = " "; string textTemplate = Boundary + " Content-Disposition: form-data; name="{0}"; filename="{1}" Content-Type: {2} "; // 头数据 string data = String.Format(textTemplate, fieldName, filename, contentType); byte[] bytes = encoding.GetBytes(data); // 尾数据 byte[] endBytes = encoding.GetBytes(end); // 合成后的数组 byte[] fieldData = new byte[bytes.Length + fileBytes.Length + endBytes.Length]; bytes.CopyTo(fieldData, 0); // 头数据 fileBytes.CopyTo(fieldData, bytes.Length); // 文件的二进制数据 endBytes.CopyTo(fieldData, bytes.Length + fileBytes.Length); // return fieldData; } public string Boundary { get { string[] bArray, ctArray; string contentType = ContentType; ctArray = contentType.Split(';'); if (ctArray[0].Trim().ToLower() == "multipart/form-data") { bArray = ctArray[1].Split('='); return "--" + bArray[1]; } return null; } } public string ContentType { get { if (HttpContext.Current == null) { return "multipart/form-data; boundary=---------------------------7d5b915500cee"; } return HttpContext.Current.Request.ContentType; } } }}using System;using System.Drawing;using System.Collections;using System.ComponentModel;using System.Windows.Forms;using System.Data;using UploadData.Common;using System.IO;namespace UploadDataWin{ public class frmUpload : System.Windows.Forms.Form { private System.Windows.Forms.Label lblAmigoToken; private System.Windows.Forms.TextBox txtAmigoToken; private System.Windows.Forms.Label lblFilename; private System.Windows.Forms.TextBox txtFilename; private System.Windows.Forms.Button btnBrowse; private System.Windows.Forms.TextBox txtFileData; private System.Windows.Forms.Label lblFileData; private System.Windows.Forms.Button btnUpload; private System.Windows.Forms.OpenFileDialog openFileDialog1; private System.Windows.Forms.TextBox txtResponse; private System.ComponentModel.Container components = null; public frmUpload() { InitializeComponent(); } protected override void Dispose(bool disposing) { if (disposing) { if (components != null) { components.Dispose(); } } base.Dispose(disposing); } private void InitializeComponent() { this.lblAmigoToken = new System.Windows.Forms.Label(); this.txtAmigoToken = new System.Windows.Forms.TextBox(); this.lblFilename = new System.Windows.Forms.Label(); this.txtFilename = new System.Windows.Forms.TextBox(); this.btnBrowse = new System.Windows.Forms.Button(); this.txtFileData = new System.Windows.Forms.TextBox(); this.lblFileData = new System.Windows.Forms.Label(); this.btnUpload = new System.Windows.Forms.Button(); this.openFileDialog1 = new System.Windows.Forms.OpenFileDialog(); this.txtResponse = new System.Windows.Forms.TextBox(); this.SuspendLayout(); // // lblAmigoToken // this.lblAmigoToken.Location = new System.Drawing.Point(40, 48); this.lblAmigoToken.Name = "lblAmigoToken"; this.lblAmigoToken.Size = new System.Drawing.Size(72, 23); this.lblAmigoToken.TabIndex = 0; this.lblAmigoToken.Text = "AmigoToken"; // // txtAmigoToken // this.txtAmigoToken.Location = new System.Drawing.Point(120, 48); this.txtAmigoToken.Name = "txtAmigoToken"; this.txtAmigoToken.Size = new System.Drawing.Size(248, 21); this.txtAmigoToken.TabIndex = 1; this.txtAmigoToken.Text = ""; // // lblFilename // this.lblFilename.Location = new System.Drawing.Point(40, 96); this.lblFilename.Name = "lblFilename"; this.lblFilename.Size = new System.Drawing.Size(80, 23); this.lblFilename.TabIndex = 2; this.lblFilename.Text = "Filename"; // // txtFilename // this.txtFilename.Location = new System.Drawing.Point(120, 96); this.txtFilename.Name = "txtFilename"; this.txtFilename.Size = new System.Drawing.Size(248, 21); this.txtFilename.TabIndex = 3; this.txtFilename.Text = ""; // // btnBrowse // this.btnBrowse.Location = new System.Drawing.Point(296, 144); this.btnBrowse.Name = "btnBrowse"; this.btnBrowse.TabIndex = 4; this.btnBrowse.Text = "浏览"; this.btnBrowse.Click += new System.EventHandler(this.btnBrowse_Click); // // txtFileData // this.txtFileData.Location = new System.Drawing.Point(120, 144); this.txtFileData.Name = "txtFileData"; this.txtFileData.Size = new System.Drawing.Size(168, 21); this.txtFileData.TabIndex = 5; this.txtFileData.Text = ""; // // lblFileData // this.lblFileData.Location = new System.Drawing.Point(40, 144); this.lblFileData.Name = "lblFileData"; this.lblFileData.Size = new System.Drawing.Size(72, 23); this.lblFileData.TabIndex = 6; this.lblFileData.Text = "FileData"; // // btnUpload // this.btnUpload.Location = new System.Drawing.Point(48, 184); this.btnUpload.Name = "btnUpload"; this.btnUpload.TabIndex = 7; this.btnUpload.Text = "Upload"; this.btnUpload.Click += new System.EventHandler(this.btnUpload_Click); // // txtResponse // this.txtResponse.Location = new System.Drawing.Point(136, 184); this.txtResponse.Multiline = true; this.txtResponse.Name = "txtResponse"; this.txtResponse.Size = new System.Drawing.Size(248, 72); this.txtResponse.TabIndex = 8; this.txtResponse.Text = ""; // // frmUpload // this.AutoScaleBaseSize = new System.Drawing.Size(6, 14); this.ClientSize = new System.Drawing.Size(400, 269); this.Controls.Add(this.txtResponse); this.Controls.Add(this.btnUpload); this.Controls.Add(this.lblFileData); this.Controls.Add(this.txtFileData); this.Controls.Add(this.btnBrowse); this.Controls.Add(this.txtFilename); this.Controls.Add(this.lblFilename); this.Controls.Add(this.txtAmigoToken); this.Controls.Add(this.lblAmigoToken); this.Name = "frmUpload"; this.Text = "frmUpload"; this.ResumeLayout(false); } [STAThread] static void Main() { Application.Run(new frmUpload()); } private void btnUpload_Click(object sender, System.EventArgs e) { // 非空检验 if (txtAmigoToken.Text.Trim() == "" || txtFilename.Text == "" || txtFileData.Text.Trim() == "") { MessageBox.Show("Please fill data"); return; } // 所要上传的文件路径 string path = txtFileData.Text.Trim(); // 检查文件是否存在 if (!File.Exists(path)) { MessageBox.Show("{0} does not exist!", path); return; } // 读文件流 FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read); // 这部分需要完善 string ContentType = "application/octet-stream"; byte[] fileBytes = new byte[fs.Length]; fs.Read(fileBytes, 0, Convert.ToInt32(fs.Length)); // 生成需要上传的二进制数组 CreateBytes cb = new CreateBytes(); // 所有表单数据 ArrayList bytesArray = new ArrayList(); // 普通表单 bytesArray.Add(cb.CreateFieldData("FileName", txtFilename.Text)); bytesArray.Add(cb.CreateFieldData("AmigoToken", txtAmigoToken.Text)); // 文件表单 bytesArray.Add(cb.CreateFieldData("FileData", path , ContentType, fileBytes)); // 合成所有表单并生成二进制数组 byte[] bytes = cb.JoinBytes(bytesArray); // 返回的内容 byte[] responseBytes; // 上传到指定Url bool uploaded = cb.UploadData("http://localhost/UploadData/UploadAvatar.aspx", bytes, out responseBytes); // 将返回的内容输出到文件 using (FileStream file = new FileStream(@"c: esponse.text", FileMode.Create, FileAccess.Write, FileShare.Read)) { file.Write(responseBytes, 0, responseBytes.Length); } txtResponse.Text = System.Text.Encoding.UTF8.GetString(responseBytes); } private void btnBrowse_Click(object sender, System.EventArgs e) { if (openFileDialog1.ShowDialog() == DialogResult.OK) { txtFileData.Text = openFileDialog1.FileName; } } }} 
