asp:upload postedfile lost during postback

I am using an asp:upload control to upload an image and am using the postedfile property to insert the path to the database. In my form I have a dropdown with autopostback=true where the user can select a topic to populate a checkbox list of categories. During that postback, the postedfile value is being lost and after a little research I have discovered that the pos开发者_JAVA技巧ted file value is not maintained in viewstate for security reasons. Has anybody else found out how to get around this?

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That's how it works. The value of a intput type="file" is never used on parsing an HTML page. That's a huge security risk, so no modern browser will allow them to 'retain' values. So in ASP.NET, every postback "loses" the value.

On any postback with a file in the input control, be sure to save the value somewhere you can get to it later.

Or don't design a form that uses a file upload to have multiple postbacks. Perhaps consider wrapping your drop down list and associated control in an UpdatePanel so the file upload doesn't get cleared.

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The value attribute of an input file element simply cannot be set by anything except user interaction. That's the way it works, and that will not change due to security concerns. That said, your solution is to eliminate the postback.

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I would try to load the checkbox list via JavaScript/AJAX, possibly saving the values of the checkbox list to a hidden field so I can retain the values on a postback.

This may not be ideal, but if you want to do this all with no postbacks, at some point your going to have to use JavaScript.

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You could try the AsynchFileUpload control in the AjaxControlToolkit, but there isn't a workaround for the standard fileupload unless you save the file to a temporary folder and load a file list from that temp folder.