I started new clear Main Window project,
There are 4 Objects: MainWindow, centralWidget, menubar, and statusbar.
I need to set default layout inside the window, so probably for centralWidget.
But I didnt found way how to do it.
I can get LayoutWidget with some particular size into centralWidget.
But I want to set layout for the whole centralWidget.
Add some widgets to the central widget first.
Then select the central widget and use the "Layout in a Grid", "Layout Vertically", etc buttons on the toolbar to add a main layout.
The layouts in the "Widget Box" side-bar are used for adding child layouts to a main layout.
pyqt designer and layout for central widget