Events

Widget events and user input handling.

Widgets emit events such as LV_EVENT_CLICKED, LV_EVENT_VALUE_CHANGED, LV_EVENT_DRAW_MAIN, and LV_EVENT_KEY. You register a callback with lv_obj_add_event_cb() and receive an lv_event_t pointer from which you read the code, target, and user data. The examples cover basic wiring, bubbling, custom event codes, and reading input device state inside a handler.

Event bubbling to a parent

Handle clicks on child buttons from a single container callback.

A 290x200 container uses LV_FLEX_FLOW_ROW_WRAP and holds 30 small buttons, each flagged with LV_OBJ_FLAG_EVENT_BUBBLE. One LV_EVENT_CLICKED callback on the container reads lv_event_get_target_obj to identify which button was clicked and paints its background red; clicks on the container itself are ignored.

Handle multiple button events

Report the most recent button event on a second label.

A centered button with a Click me! label is paired with an info label on the active screen. A single callback subscribed with LV_EVENT_ALL switches on lv_event_get_code and writes the name of the latest event (LV_EVENT_PRESSED, LV_EVENT_CLICKED, LV_EVENT_LONG_PRESSED, LV_EVENT_LONG_PRESSED_REPEAT) into the info label.

Click event on a button

Update a button's label with an incrementing counter on each click.

A button with a child label is placed on the active screen. An LV_EVENT_CLICKED callback retrieves the button, updates its label with a static incrementing counter, and logs Clicked.

Custom drawing on draw task events

Draw a pulsing red circle on top of a container with a draw task callback.

A 200x200 container is centered and flagged with LV_OBJ_FLAG_SEND_DRAW_TASK_EVENTS. An LV_EVENT_DRAW_TASK_ADDED callback inspects the draw task and, when base_dsc->part is LV_PART_MAIN, calls lv_draw_rect to paint a pink circle with a red border and outline. A 30 ms lv_timer_t bounces a size counter between 0 and 50 and invalidates the container each tick to animate the circle.

Click streaks (single, double, triple)

React to single, double, and triple click events plus the short-click streak count.

A button is registered with four event callbacks: LV_EVENT_SHORT_CLICKED reads lv_indev_get_short_click_streak() and writes the count to a separate label; LV_EVENT_SINGLE_CLICKED, LV_EVENT_DOUBLE_CLICKED, and LV_EVENT_TRIPLE_CLICKED each set the button's label to a matching string.

Event trickle to children

Forward pressed state from a flex container down to its children.

A 290x200 container with LV_FLEX_FLOW_ROW_WRAP holds nine small sub-containers, each with a numbered label. The container is flagged with LV_OBJ_FLAG_EVENT_TRICKLE so its input events reach the children; a single white-on-black style is added to the container for LV_STATE_PRESSED and to each sub-container for LV_STATE_FOCUSED, so pressing the container flips the whole group to the dark style.