Fcitx provides several abstraction of user interface element, in order to display them on different user interface implementation. Basically, there is a input window, with four text field.

There is also a user interface element called status, basically it defines a switch button. The icon name rule can be defined by user interface itself. (Defined in fcitx/ui.h)

    /**
     * @brief Fcitx Status icon to be displayed on the UI
     **/
    typedef struct _FcitxUIStatus {
        /**
         * @brief status name, will not displayed on the UI.
         **/
        char name[MAX_STATUS_NAME + 1];
        /**
         * @brief short desription for this status, can be displayed on the UI
         **/
        char shortDescription[MAX_STATUS_SDESC + 1];
        /**
         * @brief long description for this status, can be displayed on the UI
         **/
        char longDescription[MAX_STATUS_LDESC + 1];
        /**
         * @brief toogle function
         **/
        void (*toggleStatus)(void *arg);
        /**
         * @brief get current value function
         **/
        boolean (*getCurrentStatus)(void *arg);
        /**
         * @brief private data for the UI implementation
         **/
        void *priv;
        /**
         * @brief extra argument for tooglefunction
         **/
        void* arg;
    } FcitxUIStatus;
            

Short Description and Long Description is tend to be display on the user interface, the addon should have it translated before register the status.

Another user interface element is a menu, which currently only support by fcitx-classic-ui and fcitx-light-ui. Due to the limitation of kimpanel, it cannot support fcitx style menu currently. (Defined in fcitx/ui.h)

    /**
     * @brief a menu entry in a menu.
     **/
    typedef struct _MenuShell
    {
        /**
         * @brief The displayed string
         **/
        char tipstr[MAX_MENU_STRING_LENGTH + 1];
        /**
         * @brief Can be used by ui to mark it's selected or not.
         **/
        int  isselect;
        /**
         * @brief The type of menu shell
         **/
        MenuShellType type;
        /**
         * @brief the submenu to this entry
         **/
        struct _FcitxUIMenu *subMenu;
    } MenuShell;

    /**
     * @brief Fcitx Menu Component, a UI doesn't need to support it,
     *        This struct is used by other module to register a menu.
     **/
    typedef struct _FcitxUIMenu {
        /**
         * @brief shell entries for this menu
         **/
        UT_array shell;
        /**
         * @brief menu name, can be displayed on the ui
         **/
        char name[MAX_MENU_STRING_LENGTH + 1];
        /**
         * @brief you might want to bind the menu on a status icon, but this is only a hint,
         * depends on the ui implementation
         **/
        char candStatusBind[MAX_STATUS_NAME + 1];
        /**
         * @brief update the menu content
         **/
        UpdateMenuShellFunction UpdateMenuShell;
        /**
         * @brief function for process click on a menu entry
         **/
        MenuActionFunction MenuAction;
        /**
         * @brief private data for this menu
         **/
        void *priv;
        /**
         * @brief ui implementation private
         **/
        void *uipriv;
        /**
         * @brief this is sub menu or not
         **/
        boolean isSubMenu;
        /**
         * @brief mark of this menu
         **/
        int mark;
    } FcitxUIMenu;
            

Module who want to use menu or status icon should use RegisterStatus and RegisterMenu function. A User interface in order to support status icon or menu, should implement UpdateStatus, RegisterStatus, RegisterMenu callbacks.