shared contextGL

Hi,
I code this below in main.cpp to have the shared with mywidget1 (mywidget1 designer from designer).

Code:

---

MainForm w;
// Instantiate the viewers.
MyWidget top (&w, "shared", w.myWidget1);

---

Can I sure that top is sharing context of widget1?
Previously I inserted a widget 'top' from designer; so I had also w.top without declare it in main.cpp. How can I do sharing using 'top' inserted from designer?
thanks