Android : Using ActivityView class in Android Lollipop

I am developing an app allowing to launch another app in a sub window includes in the first app (sorry for the repetition of the word "app"). For this I am using the ActivityView class (only available in Android 5.0).

I managed to launch the second app in the sub window but my problem is the keyboard is not visible. Indeed in this app (the second one launched in the sub window), I have an button allowing to show the keyboard (function toogleSoftInput() in InputManager.class). So when I launch this app in the sub window and click on the button, it catches the onClick event but the keyboard doesn't appear.

Would anybody know how could I display the keyboard in the second app launched in the the sub window included in my main app?

I am currently using AOSP

Thanks in advance