delete layout() / setLayout issue

[marcel]

You better use a QStackedWidget.

I think the problem is that you add widgets to both layouts, and you delete one of them. You should add the widgets to the second layout after the first one is deleted.
This code:

mainLayoutBigg  = new QGridLayout((QWidget*)this);
mainLayoutSmall = new QGridLayout((QWidget*)this);

mainLayoutBigg  = new QGridLayout((QWidget*)this);
mainLayoutSmall = new QGridLayout((QWidget*)this);

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Creating the layouts with parents causes them to be set just as using setLayout.