asp.net响应双重内容类型

Question

i am sending a large amount of excel content data to the browser using Page.Response.Write("") in a for loop.

before starting the loop i am changing the conetnt type of the reponse.context property to "ms-excel".

if i have an exception during that for loop , i try to popup an error message to the browser by registering an HTML startup script block and Write it to the browser. before the write i change back the content type to be text/html. but i get an error that say that is not possible to change the content type after sending the HTTP Headers.

How to notify the browser about an error that occured during that for loop? Is it possible to have more that one respone to the same browser tab? by the way,right now i don't want to use ASP.NET AJAX.

Answer 1

Did you try Response.ClearHeaders(); before changing the context type?

If that doesn't work because your Response.Write is causing problems, you might think about going the route of building a string before deciding your content type and then setting the headers.

• Loop trough the content and add to a StringBuilder
• If no error, set contenttype to ms-excel and write out SB
• If there is an error, leave contenttype as it is write out your error message as needed.

Answer 2

Page.Response.Write("") will send data to the browser. When you do that the browser needs to know the type of content it gets in order to render it correct. If you already told the browser what kind of content you have(and even if you don't, you are already sening data with Response.Write, it will use the default value which I think is text/html) then you can't take it back. Whatever you are saying to the client is said and you can't take it back. The way to solve your problem is to cache the reply as suggested by Doozer.

/Tibi