When a focus window is closed, the entire region is not the focus window.

Close focus dock?then No dock is focus.

Well… yes. There is just no code to re-focus another Dockable. It’s no bug, just a feature that was never implemented.

Whether to consider the next version to achieve it?
or Is there any way I deal with it manually?

control.addFocusListener(new CFocusListener() {

            public void focusGained(CDockable dockable) {
                selView = dockable;

            public void focusLost(CDockable dockable) {
                if (selView == dockable) {
                    selView = null;

Unless control.getCDockableCount() ==0 ,Otherwise selView != null.
but now close focus dock,no dock focusGained,selView == null.