As I said earlier, we didn’t test our solution to using the ModalPopupExtender in SharePoint in all situations. Today we made a start to do so. To indicate our successrate: we now use window.showModalDialog with some extra pages…
Getting the ModalPopupExtender from the Ajax Control Toolkit to work (decently) in SharePoint was not exactly a walk in the park. With a default SharePoint installation, the modal popup is partly positioned ‘outside’ of the page (you only see the bottom right part of the popup in the top left corner of the browser). Postbacks are not executed or executed poorly and the page gets garbled up. A possible solution for the positioning of the popup is to set the X and Y property of the ModalPopupExtender. Downside is you never know (for sure) if the popup is positioned inside the visible part of the browser because of things like non-maximized browser, different resolutions and so on.
Today we seem to have solved our issues with the ModalPopupExtender in SharePoint. We haven’t tested it in all scenario’s yet, but we’ll get to that. At this point everything looks the way it is supposed to. And it seems to work, too… ;).