Could you explain in more detail what exactly you need to perform as validation. I am asking this, because a lot of the setup depends on your needs:
- RadWindow closes because the postback disposes it. To avoid this you need to use AJAX: http://www.telerik.com/help/aspnet-ajax/window-ajaxifying.html.
- With file uploads, however, you need a full postback at some point so the files can travel to the destination folder, so using AJAX may not be an option.
- You can consider using the VisibleOnPageLoad property of theRadWindow and resetting it to false when needed: http://www.telerik.com/help/aspnet-ajax/window-troubleshooting-opening-from-server.html.
- You can also consider moving this upload functionality to a separate aspx page that you can load in the RadWindow. This is, perhaps, the simplest option, because at this point the content page has its own context and postbacks inside do not affect the parent or the RadWindow.
I also advise that you keep RadWindows whose ContentTemplate is used outside of a RadWindowManager.
I hope this information helps you choose the approach most suitable for your setup.
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