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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 posted file value is not maintained in viewstate for security reasons. Has anybody else found out how to get around this?
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.