import QtQuick 2.9
import QtQuick.Controls 2.3

ApplicationWindow {
    id: window
    visible: true

    Button {
        id: button
        focus: true
        // Works
//        Component.onCompleted: print(ApplicationWindow.window.activeFocusItem)
        // ".onActiveFocusItemChanged" is not available due to component versioning.
        ApplicationWindow.window.onActiveFocusItemChanged: print("activeFocusItem", activeFocusItem)
        // Works
//        ApplicationWindow.onActiveFocusControlChanged: print("activeFocusControl", activeFocusControl)
    }
}