gtk::entry and textview doesn't accept keyboard input?

[明覺 <shi minjue gmail com>]

I'm a newbie in gtkmm programming, I found that my gtk::entry doesn't
accept keyboard input, but it can accept mouse input, what's wrong
with it? I add the control in this way:

Gtk::TextView mathinput;
pack_start(mathinput, Gtk::PACK_SHRINK);

how could i make them accept keyboard input? thanks
-- 
不苦不樂正念正智
Gnu.Linux.(Debian|gNewSense).Gnome.(Mozilla|Gmail|Evolution|Scim|Flashplayer)
Microsoft.Windows.(Vista|XP).(QQ|Game|Notepad++) Gcc.Gtkmm.Opengl