Adding custom QWidget during runtime

I'm trying to implement a custom widget hierarchy: QMainWindow -> QFrame -> MyWidget -> QFrame -> MySubWidget

Here is how MyWidget class looks like:

    class MyWidget : public QWidget {
        Q_OBJECT
    public:
        MyWidget(QWidget *parent = 0, ...);
        ...
    public slots:
        void SlotFunction(int i);
        ...
    private:
        MySubWidget *sub_w;
        QFrame *sub_frame;
        ...
    }

If I try to create an MySubWidget during MyWidget constructor, then all MySubWidget elements are shown as intended:

    MyWidget::MyWidget (...) : QWidget(parent) {
        ...
        sub_frame = new QFrame(this);
        ...
        sub_w = new MySubWidget(sub_frame); // commented out on a runtime test
    }

But if I try to add subwidget during runtime, sub_frame remains blank. I.e. signal reaction:

    void MyWidget::SlotFunction(int i) {
        sub_w = new MySubWidget(sub_frame); // update, repaint, show and hide methods aren't helphul
    }