winform下载的问题

Question

public static  void DownloadFile(string fileName,string showName)
{
string physicalFilePath = GetDianDanHeTongImagePath()+@"\"+fileName;
FileStream stream=null;
try 
{
stream = new FileStream(physicalFilePath, FileMode.Open, FileAccess.Read, FileShare.Read);
int bufSize = (int)stream.Length;
byte[] buf = new byte[bufSize];
int bytesRead = stream.Read(buf, 0, bufSize);
HttpContext.Current.Response.ContentType = "application/octet-stream";
HttpContext.Current.Response.AddHeader("Content-Disposition","attachment; filename=\"" + HttpUtility.UrlEncode(showName,System.Text.Encoding.UTF8) + "\"");
HttpContext.Current.Response.OutputStream.Write(buf, 0, bytesRead);
HttpContext.Current.Response.End();
stream.Close();
}
finally {                                                                                                                  

}
}文件存在局网服务器下，为什么执行到
HttpContext.Current.Response.ContentType 的时候就说：未将对像引用到实例呢？

Answer 1

因为你的Response是null
建议你用webclient来做，它有DownloadData(path)和OpenRead(path)方法

Answer 2

谢谢楼上，我的方法已经实现了，贴出代码，以备后来来查：System.Windows.Forms.SaveFileDialog saveFile = new SaveFileDialog();
saveFile.Filter = "*.tif|*.TIF|*.jpg|*.JPG|*.gif|*.GIF";
string SourceURL = CRM.Sys.Utility.CommonFun.GetDianDanHeTongImagePath()+@"\"+fileName;
DialogResult result = saveFile.ShowDialog();
//saveFile.
if(result ==DialogResult.Cancel)
return;
string DestPath = saveFile.FileName;
System.Net.WebClient webClient=new System.Net.WebClient();
Stream stream = webClient.OpenRead(SourceURL);
byte[] arrByte = new byte[1024];
long completedByteCount = 0;
if (File.Exists(DestPath))
File.Delete(DestPath);
FileStream fStream = new FileStream(DestPath,FileMode.CreateNew,FileAccess.Write);
while(true)
{
int readCnt = stream.Read(arrByte,0,1024);
if(readCnt==0) 
break;      
fStream.Write(arrByte,0,readCnt);
completedByteCount += readCnt;
}              
stream.Close();
fStream.Close();///不过现在有一个小问题时，在弹出SaveFileDialog的时候，我不知如何初始化"保存文件的名字"