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