.. _events: ====== Events ====== Events are triggered in LVGL when something happens which might be interesting to the user, e.g. when an object: - is clicked - is scrolled - has its value changed - is redrawn, etc. Add events to the object ************************ The user can assign callback functions to an object to see its events. In practice, it looks like this: .. code:: c lv_obj_t * btn = lv_btn_create(lv_scr_act()); lv_obj_add_event(btn, my_event_cb, LV_EVENT_CLICKED, NULL); /*Assign an event callback*/ ... static void my_event_cb(lv_event_t * event) { printf("Clicked\n"); } In the example :cpp:enumerator:`LV_EVENT_CLICKED` means that only the click event will call ``my_event_cb``. See the `list of event codes <#event-codes>`__ for all the options. :cpp:enumerator:`LV_EVENT_ALL` can be used to receive all events. The last parameter of :cpp:func:`lv_obj_add_event` is a pointer to any custom data that will be available in the event. It will be described later in more detail. More events can be added to an object, like this: .. code:: c lv_obj_add_event(obj, my_event_cb_1, LV_EVENT_CLICKED, NULL); lv_obj_add_event(obj, my_event_cb_2, LV_EVENT_PRESSED, NULL); lv_obj_add_event(obj, my_event_cb_3, LV_EVENT_ALL, NULL); /*No filtering, receive all events*/ Even the same event callback can be used on an object with different ``user_data``. For example: .. code:: c lv_obj_add_event(obj, increment_on_click, LV_EVENT_CLICKED, &num1); lv_obj_add_event(obj, increment_on_click, LV_EVENT_CLICKED, &num2); The events will be called in the order as they were added. Other objects can use the same *event callback*. Remove event(s) from an object ****************************** Events can be removed from an object with the :cpp:expr:`lv_obj_remove_event(obj, event_cb)` function Event codes *********** The event codes can be grouped into these categories: - Input device events - Drawing events - Other events - Special events - Custom events All objects (such as Buttons/Labels/Sliders etc.) regardless their type receive the *Input device*, *Drawing* and *Other* events. However, the *Special events* are specific to a particular widget type. See the `widgets' documentation `__ to learn when they are sent, *Custom events* are added by the user and are never sent by LVGL. The following event codes exist: Input device events ------------------- - :cpp:enumerator:`LV_EVENT_PRESSED`: An object has been pressed - :cpp:enumerator:`LV_EVENT_PRESSING`: An object is being pressed (called continuously while pressing) - :cpp:enumerator:`LV_EVENT_PRESS_LOST`: An object is still being pressed but slid cursor/finger off of the object - :cpp:enumerator:`LV_EVENT_SHORT_CLICKED`: An object was pressed for a short period of time, then released. Not called if scrolled. - :cpp:enumerator:`LV_EVENT_LONG_PRESSED`: An object has been pressed for at least the ``long_press_time`` specified in the input device driver. Not called if scrolled. - :cpp:enumerator:`LV_EVENT_LONG_PRESSED_REPEAT`: Called after ``long_press_time`` in every ``long_press_repeat_time`` ms. Not called if scrolled. - :cpp:enumerator:`LV_EVENT_CLICKED`: Called on release if an object did not scroll (regardless of long press) - :cpp:enumerator:`LV_EVENT_RELEASED`: Called in every case when an object has been released - :cpp:enumerator:`LV_EVENT_SCROLL_BEGIN`: Scrolling begins. The event parameter is ``NULL`` or an :cpp:type:`lv_anim_t` ``*`` with a scroll animation descriptor that can be modified if required. - :cpp:enumerator:`LV_EVENT_SCROLL_THROW_BEGIN`: Sent once when the object is released while scrolling but the "momentum" still keeps the content scrolling. - :cpp:enumerator:`LV_EVENT_SCROLL_END`: Scrolling ends. - :cpp:enumerator:`LV_EVENT_SCROLL`: An object was scrolled - :cpp:enumerator:`LV_EVENT_GESTURE`: A gesture is detected. Get the gesture with :cpp:expr:`lv_indev_get_gesture_dir(lv_indev_get_act())` - :cpp:enumerator:`LV_EVENT_KEY`: A key is sent to an object. Get the key with :cpp:expr:`lv_indev_get_key(lv_indev_get_act())` - :cpp:enumerator:`LV_EVENT_FOCUSED`: An object is focused - :cpp:enumerator:`LV_EVENT_DEFOCUSED`: An object is unfocused - :cpp:enumerator:`LV_EVENT_LEAVE`: An object is unfocused but still selected - :cpp:enumerator:`LV_EVENT_HIT_TEST`: Perform advanced hit-testing. Use :cpp:struct:`lv_hit_test_info_t` ``* a =`` :cpp:expr:`lv_event_get_hit_test_info(e)` and check if ``a->point`` can click the object or not. If not set ``a->res = false`` Drawing events -------------- - :cpp:enumerator:`LV_EVENT_COVER_CHECK`: Check if an object fully covers an area. The event parameter is :cpp:struct:`lv_cover_check_info_t` ``*``. - :cpp:enumerator:`LV_EVENT_REFR_EXT_DRAW_SIZE`: Get the required extra draw area around an object (e.g. for a shadow). The event parameter is :cpp:type:`lv_coord_t` ``*`` to store the size. Only overwrite it with a larger value. - :cpp:enumerator:`LV_EVENT_DRAW_MAIN_BEGIN`: Starting the main drawing phase. - :cpp:enumerator:`LV_EVENT_DRAW_MAIN`: Perform the main drawing - :cpp:enumerator:`LV_EVENT_DRAW_MAIN_END`: Finishing the main drawing phase - :cpp:enumerator:`LV_EVENT_DRAW_POST_BEGIN`: Starting the post draw phase (when all children are drawn) - :cpp:enumerator:`LV_EVENT_DRAW_POST`: Perform the post draw phase (when all children are drawn) - :cpp:enumerator:`LV_EVENT_DRAW_POST_END`: Finishing the post draw phase (when all children are drawn) - :cpp:enumerator:`LV_EVENT_DRAW_PART_BEGIN`: Starting to draw a part. The event parameter is :cpp:struct:`lv_obj_draw_dsc_t` ``*``. Learn more :ref:`drawing`. - :cpp:enumerator:`LV_EVENT_DRAW_PART_END`: Finishing to draw a part. The event parameter is :cpp:struct:`lv_obj_draw_dsc_t` ``*``. Learn more :ref:`drawing`. In ``LV_EVENT_DRAW_...`` events it's not allowed to adjust the widgets' properties. E.g. you can not call :cpp:func:`lv_obj_set_width`. In other words only ``get`` functions can be called. Other events ------------ - :cpp:enumerator:`LV_EVENT_DELETE`: Object is being deleted - :cpp:enumerator:`LV_EVENT_CHILD_CHANGED`: Child was removed/added - :cpp:enumerator:`LV_EVENT_CHILD_CREATED`: Child was created, always bubbles up to all parents - :cpp:enumerator:`LV_EVENT_CHILD_DELETED`: Child was deleted, always bubbles up to all parents - :cpp:enumerator:`LV_EVENT_SIZE_CHANGED`: Object coordinates/size have changed - :cpp:enumerator:`LV_EVENT_STYLE_CHANGED`: Object's style has changed - :cpp:enumerator:`LV_EVENT_BASE_DIR_CHANGED`: The base dir has changed - :cpp:enumerator:`LV_EVENT_GET_SELF_SIZE`: Get the internal size of a widget - :cpp:enumerator:`LV_EVENT_SCREEN_UNLOAD_START`: A screen unload started, fired immediately when lv_scr_load/lv_scr_load_anim is called - :cpp:enumerator:`LV_EVENT_SCREEN_LOAD_START`: A screen load started, fired when the screen change delay is expired - :cpp:enumerator:`LV_EVENT_SCREEN_LOADED`: A screen was loaded, called when all animations are finished - :cpp:enumerator:`LV_EVENT_SCREEN_UNLOADED`: A screen was unloaded, called when all animations are finished Special events -------------- - :cpp:enumerator:`LV_EVENT_VALUE_CHANGED`: The object's value has changed (i.e. slider moved) - :cpp:enumerator:`LV_EVENT_INSERT`: Text is being inserted into the object. The event data is ``char *`` being inserted. - :cpp:enumerator:`LV_EVENT_REFRESH`: Notify the object to refresh something on it (for the user) - :cpp:enumerator:`LV_EVENT_READY`: A process has finished - :cpp:enumerator:`LV_EVENT_CANCEL`: A process has been canceled Custom events ------------- Any custom event codes can be registered by ``uint32_t MY_EVENT_1 =`` :cpp:func:`lv_event_register_id` They can be sent to any object with :cpp:expr:`lv_event_send(obj, MY_EVENT_1, &some_data)` Sending events ************** To manually send events to an object, use :cpp:expr:`lv_event_send` ``(obj, &some_data)``. For example, this can be used to manually close a message box by simulating a button press (although there are simpler ways to do this): .. code:: c /*Simulate the press of the first button (indexes start from zero)*/ uint32_t btn_id = 0; lv_event_send(mbox, LV_EVENT_VALUE_CHANGED, &btn_id); Refresh event ------------- :cpp:enumerator:`LV_EVENT_REFRESH` is a special event because it's designed to let the user notify an object to refresh itself. Some examples: - notify a label to refresh its text according to one or more variables (e.g. current time) - refresh a label when the language changes - enable a button if some conditions are met (e.g. the correct PIN is entered) - add/remove styles to/from an object if a limit is exceeded, etc Fields of lv_event_t ******************** :cpp:type:`lv_event_t` is the only parameter passed to the event callback and it contains all data about the event. The following values can be gotten from it: - :cpp:expr:`lv_event_get_code(e)`: get the event code - :cpp:expr:`lv_event_get_current_target(e)`: get the object to which an event was sent. I.e. the object whose event handler is being called. - :cpp:expr:`lv_event_get_target(e)`: get the object that originally triggered the event (different from :cpp:func:`lv_event_get_target` if `event bubbling <#event-bubbling>`__ is enabled) - :cpp:expr:`lv_event_get_user_data(e)`: get the pointer passed as the last parameter of :cpp:func:`lv_obj_add_event`. - :cpp:expr:`lv_event_get_param(e)`: get the parameter passed as the last parameter of :cpp:func:`lv_event_send` Event bubbling ************** If :cpp:expr:`lv_obj_add_flag(obj, LV_OBJ_FLAG_EVENT_BUBBLE)` is enabled all events will be sent to an object's parent too. If the parent also has :cpp:enumerator:`LV_OBJ_FLAG_EVENT_BUBBLE` enabled the event will be sent to its parent and so on. The *target* parameter of the event is always the current target object, not the original object. To get the original target call :cpp:expr:`lv_event_get_target_obj(e)` in the event handler. Examples ******** .. include:: ../examples/event/index.rst API ***