QVTKOpenGLWidget does not automatically update the screen initially

Use the QVTKOpenGLNativeWidget in your project to display the point cloud model.
Use

VTKRenderWindow->Render();

statement can realize the subsequent real-time update of the screen. However, in the software interface after the initial load, the screen does not automatically update, meaning that after the software is running, I have to drag the VTK window with the mouse to change the view so that the VTK window refreshes for the first time, and then the VTK window updates in real time as I do other work. But if I don't do it at the beginning, I don't drag the VTK window with the mouse, the VTK window doesn't refresh, and the rest of my work doesn't update in real time.
What is the situation and how can I ensure that VTK Windows are updated in real time?