ASP.NET Excel export encoding problem

Question

I'm doing some Excel Exports on the ASP.NET Site. Everything works except of the Encoding. When I open it in Excel, it looks like this:

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This is my code:

Response.Clear();
Response.ContentType = "application/ms-excel";
Response.AddHeader("Content-Disposition", "inline;filename=NachkalkGeraete.xls;");
var writer = new HtmlTextWriter(Response.Output);

SomeControl.RenderControl(writer); /* FormView, Table, DataGrid... */

Response.End();

I've already tried explicitly set the Encoding.. but no change occured:

Response.Clear();
Response.ContentType = "application/vnd.ms-excel";
Response.AddHeader("Content-Disposition", "attachment; filename=NachkalkGeraete.xls");

Response.BufferOutput = true;
Response.ContentEncoding = System.Text.Encoding.UTF8;
Response.Charset = "UTF-8";
EnableViewState = false;

System.IO.StringWriter tw = new System.IO.StringWriter();
HtmlTextWriter hw = new HtmlTextWriter(tw);

SomeControl.RenderControl(hw);

Response.Write(tw.ToString());
Response.End();

What is wrong, please?

Answer 1

Well I found out that the problem could be in the header of the excel file, that it does not contain the BOM byte sequence (at the beginning of the file representing the encoding used).

So I made it this way and it works for me:

Response.Clear();
Response.AddHeader("content-disposition","attachment;filename=Test.xls");   
Response.ContentType = "application/ms-excel";
Response.ContentEncoding = System.Text.Encoding.Unicode;
Response.BinaryWrite(System.Text.Encoding.Unicode.GetPreamble());

System.IO.StringWriter sw = new System.IO.StringWriter();
System.Web.UI.HtmlTextWriter hw = new HtmlTextWriter(sw);

FormView1.RenderControl(hw);

Response.Write(sw.ToString());
Response.End();