QVTKOpenGLWidget works in constuctor but not responds to signals.

Hi, I have a QVTKOpenGLWidget in mainwindow, it’s promoted from QWidget.
I need to draw something(say cylinder, .ply) in the QVTKOpenGLWidget, and when I write code in constructor, everything is ok, but when I connect related code to a signal (an action in menu), nothing is painted when the action is triggered.
Thank you.

(For more details please see: https://stackoverflow.com/questions/55833867/qvtkopenglwidget-doesnt-respond-to-signal-while-other-widgets-in-the-same-ui)

Please see this example :