QOpenGLWidget: Cannot make uninitialized widget current

[Make it GREAT again]

I tried embedding a qwt3d object into the UI of my project. The embedding seems fine after making attempts but there is still problem to deal with.

Debug mode gives output like this QOpenGLWidget: Cannot make uninitialized widget current

, and UI does not show labels of axes as given by the image attached.

TestGui::TestGui(QWidget *parent) : QMainWindow(parent),
ui(new Ui::TestGui)
{
ui->setupUi(this);

QGridLayout *grid = new QGridLayout(ui->frame);

oPlot = new DifPlot(ui->frame);
grid->addWidget( oPlot, 0, 0 );

// Setting labels and so on.

}
DifPlot is inheritted from Qwt3D::GridPlot and explicity calls constructor of its parent class.