Before I uninstalled Qt, I forgot to delete the Qt version in qtvsaddin. As a result, there is an invalid Qt version in qtvsaddin. If I don't reinstall Qt, what should I do? Thanks.
VS add-in (aka Qt Visual Studio Tools) is independent of installed Qt versions, in the sense that the list is maintain separately. You can add and remove versions as you want (even duplicated with different names). When you remove a version in VS it should be removed from both the list view and the combo box, so if it was kept there it is probably due to a bug in the add-in.
You can check the list of versions in the Registry Editor at HKCU\Software\Digia\Versions
. You'll see there a key for each version as well as a value with the default one.
Close all instances of Visual Studio. Then remove your version from there and check that there is no value containing such version in HKCU\Software\Digia\Versions
. Modify at your risk ;) (do a backup of the key before starting).