Linux Virtual Keyboard will not set to visible

[CptN3m0]

Hello every one,

Im trying to get a virtual keyboard from ubuntu (onboard), set hidden and visible in my application, but I have some issue.

1. When I start my application using full screen

QMainWindow::showFullScreen();

the virtual keyboard isnt visible on a second widget, which I open using a button from mainwindow.
If I start my application without full screen, every thing works fine.

for hiding my keyboard Im using

system("dbus-send --type=method_call --dest=org.onboard.Onboard /org/onboard/Onboard/Keyboard org.onboard.Onboard.Keyboard.Hide");

for show it

system("dbus-send --type=method_call --dest=org.onboard.Onboard /org/onboard/Onboard/Keyboard org.onboard.Onboard.Keyboard.ToggleVisible");
    system("dbus-send --type=method_call --dest=org.onboard.Onboard /org/onboard/Onboard/Keyboard org.onboard.Onboard.Keyboard.Show");

How can I fix this issue? Is there another option to get the full screen on ubuntu of an application?