use QFrame as addStretch():

[jpn]

I'm not 100% sure if I understood the problem but I guess you could set an "expanding" size policy:

vDivider1->setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);

vDivider1->setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);

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PS. Wouldn't it be easier to use Qt Designer to handle all this?