Automatic Activity Resize

I have Android 5.1 device that has a custom function to show/hide navigation bar by broadcast sending.
The function does implement show and hide the bar, but the activity height doesn't change and after hiding there is black rectangle in place of bar. If you then restart the app the activity size is changed.
At the same application that was created by Android Studio the activity size is automatically changed after hide/show the bar.
I'd like to see the same behavior from B4A.

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