I added a new method at usb-device-manager then call it at usb-device-widget , but when I compile the project , a problem was appeared ....... Please help me check this LINK problem , thank you it looks like cannot find libspice-client-gtk-3.0.la ?CCLD libspice-client-glib-2.0.la CC spice-gtk-session.lo CC spice-widget.lo CC vncdisplaykeymap.lo CC spice-grabsequence.lo CC desktop-integration.lo CC usb-device-widget.lo usb-device-widget.c: In function 'device_added_cb': usb-device-widget.c:507:11: warning: unused variable 'state' [-Wunused-variable] guint state = spice_reget_usb_state(device); ^ CC spice-widget-cairo.lo CC spice-widget-enums.lo CCLD libspice-client-gtk-3.0.la .libs/usb-device-widget.o: In function `device_added_cb': /root/.netbeans/remote/172.26.80.71/xhx-20150710tvd-Windows-x86/F/1111/spice-gtk-0.28/gtk/usb-device-widget.c:507: undefined reference to `spice_reget_usb_state' collect2: error: ld returned 1 exit status Makefile:1201: recipe for target 'libspice-client-gtk-3.0.la' failed make[4]: *** [libspice-client-gtk-3.0.la] Error 1 make[4]: Leaving directory '/root/.netbeans/remote/172.26.80.71/xhx-20150710tvd-Windows-x86/F/1111/spice-gtk-0.28/gtk' Makefile:1636: recipe for target 'all-recursive' failed make[3]: *** [all-recursive] Error 1 make[3]: Leaving directory '/root/.netbeans/remote/172.26.80.71/xhx-20150710tvd-Windows-x86/F/1111/spice-gtk-0.28/gtk' Makefile:1084: recipe for target 'all' failed make[2]: *** [all] Error 2 make[2]: Leaving directory '/root/.netbeans/remote/172.26.80.71/xhx-20150710tvd-Windows-x86/F/1111/spice-gtk-0.28/gtk' Makefile:655: recipe for target 'all-recursive' failed make[1]: *** [all-recursive] Error 1 make[1]: Leaving directory '/root/.netbeans/remote/172.26.80.71/xhx-20150710tvd-Windows-x86/F/1111/spice-gtk-0.28' Makefile:557: recipe for target 'all' failed make: *** [all] Error 2