QOpenGLWidget in TabWidget

Hello everybody,
i am new to Qt and i hope you can help me with my problem.

In my application i have set a tabWidget as the centralwidget. The tabWidget has several tabs with QOpenGLWidgets.

With a pushButton i want to upload the data for the scene to GL.

The scenes are rendered as shown in this example: QOpenGLWidget Example

This works fine, but first i have to click on each tab to show it. Otherwise an error occurs.

So is there any way to upload my data without "shown" the QOpenGLWidget before?

Thanks!