FocusManager is not currently implemented in NoesisGUI but you can obtain the focused element asking the Keyboard object:

UIElement anyTreeElement = ...;

UIElement focusedElement = anyTreeElement.GetKeyboard().GetFocused();

Will you need logical focus, apart from keyboard focus, to be implemented?

Thanks, I didn't know how to get the instance of Keyboard class. It works very well now.

I don't think we need logical focus (FocusManager) on C# side yet. Currently we need it only on Noesis.dll side - it should behave in the same way as in WPF:
"The idea is that WPF keeps track of one or more groups of controls, each of which makes up a focus scope. Within each focus scope, a single control can have logical focus. This allows WPF to remember the control that last had focus in a group of controls and give the keyboard focus back to the proper control when a group of controls becomes active again." (from http://wpf.2000things.com/2011/05/27/309-keyboard-focus-vs-logical-focus/ )

It seems to be not a problem anymore.
Please close this ticket.

I will leave it, as it is an unimplemented feature. If more people asks for this we might work on this.

Fixed in changeset 12682