Window forms security warning while downloading/opening excel file

Question

0.00/5 (No votes)

See more:

In Window Form while downloading or opening an excel file, a warning is shown each time "The file format and extension of filenameName don't match. The file could be corrupted or unsafe. Unless you trust its source, don't open it. Do you want to open it anyway?"

How can I prevent this warning?

What I have tried:

The warning is appearing even after changing extension from .xls to .xlsx.

Code I am using:-

Response.Clear();
Response.ContentType = "application/x-msexcel"; 
Response.AddHeader("Content-Disposition", "attachment; filename=File.xls");
Response.ContentEncoding = Encoding.UTF8; 
StringWriter sw = new StringWriter();
HtmlTextWriter htw = new HtmlTextWriter(sw);
div1.RenderControl(htw);
Response.Write(sw.ToString());
Response.End();

Posted 30-Dec-18 23:20pm

TechieeGeek

Updated 31-Dec-18 5:27am

v2

Add a Solution

Comments

F-ES Sitecore 31-Dec-18 9:04am

You could try a different MIME type (ContentType), google "xlsx mime type". However the problem might be simply that you are sending html from "div1" and telling the browser that's an xlsx file, but it isn't, it's html.

Mehdi Gholam 31-Dec-18 9:07am

Html files are not XLS files hence the error, use "text/html"

TechieeGeek 2-Jan-19 5:45am

Changing the extension didn't solve any problem. Getting same message.

1 solution

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Dave Kreskowiak · Answer 1 · 2018-12-31T05:28:00

Solution 1

You're got a mime type of "application/x-msexcel", but the content of the file your writing is HTML, NOT A VALID EXCEL FILE.

Just putting something that looks like a sheet in Excel into a file does NOT make it an Excel file.

You're going to have to either change the mime type to something more appropriate for HTML content, like "text/html", or use a library, like OpenXML or ClosedXML, to generate actual Excel content. Which one of these things you do depends on what your app is expecting for content in the file.

Posted 31-Dec-18 5:28am

Dave Kreskowiak

Comments

TechieeGeek 2-Jan-19 4:55am

I tried changing the MIME type to HTML as suggested. Still I am getting the same error while opening the excel. So in such is using the external library the only solution.

Dave Kreskowiak 2-Jan-19 12:17pm

That's because an HTML file is NOT an Excel file. What you wrote to the file is not something Excel can understand. You have to use a library to write appropriate content to the file so Excel can read it.