Adding layout on groupBox

[kode]

Hi all,

I am testing some things in the QtCreator. I made simple formular with groupBox. I added grid layout to the groupBox to position all the containing objects in grid.

I am trying to do the same in cpp file (programmatically), but the layout didn't get set. I use

QGridLayout *layout = new QGridLayout;
ui->groupBox_main->setLayout(layout);

QGridLayout *layout = new QGridLayout;
ui->groupBox_main->setLayout(layout);

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where groupBox_main is the groupBox I want to set to grid. Can anyone help a little?