problem
You will get stuck and then quit when the crash QtCreator open a project, such as an ordinary open .cpp or .h files properly in the editor, build normal, normal operation, but open ui file (QtCreator automatically invoked designer).
Solution
Under Linux
delete or rename the ~/.designer/gradients.xmlfile, restart QtCreator.
(Pro-test available)
under Windows
to delete or rename the C:\Users\Administrator\.designer\gradients.xmlfile, restart QtCreator.