Control ownership

A window retains the controls passed to add_control(). Controls refer to their parent through weak_ptr. Application classes commonly retain their own shared references so they can update or reattach controls. remove_control() detaches a control; it survives if another shared owner remains.

A panel is a visual surface, not a child-control container. An embedded window can own its own controls. message and tray_icon are separate helper objects.

Avoid ownership cycles in callbacks. In particular, do not capture a control's own shared pointer in its callback:

auto check = std::make_shared<wui::button>("Remember", [] {}, wui::button_view::checkbox);
check->set_callback([weak = std::weak_ptr<wui::button>(check)] {
    if (auto control = weak.lock()) {
        bool checked = control->turned();
        // Apply checked to application state.
    }
});

Callbacks that capture this or references require the referenced objects to outlive the subscription. Unsubscribe, stop timers and join workers before releasing captured state. Retain dialogs until they are closed. See threading.