I think that the top-most black bar is composed by two GtkLabels: titleItem (the left part) and titleLocation (the right part). So, I can make they responsive to click-event by adding two lines in lister.cpp:
Code:
g_signal_connect(G_OBJECT(g_lister.titleItem), "button_press_event",
G_CALLBACK(ls_titleItem_press_event), data);
Code:
g_signal_connect(G_OBJECT(g_lister.titleLocation), "button_press_event",
G_CALLBACK(ls_titleLocation_press_event), data);
and creating two functions: ls_titleItem_press_event() and ls_titleLocation_press_event() to control goto top-menu and go up one level.