lvgl/examples/get_started/lv_example_get_started_1.c

#include "../../lvgl.h"
#if LV_BUILD_EXAMPLES

static void btn_event_cb(lv_obj_t * btn, lv_event_t event)
{
    if(event == LV_EVENT_CLICKED) {
        static uint8_t cnt = 0;
        cnt++;

        /*Get the first child of the button which is the label and change its text*/
        lv_obj_t * label = lv_obj_get_child(btn, 0);
        lv_label_set_text_fmt(label, "Button: %d", cnt);
        lv_obj_align(label, NULL, LV_ALIGN_CENTER, 0, 0);
    }
}

/**
 * Create a button with a label and react on click event.
 */
void lv_example_get_started_1(void)
{
    lv_obj_t * btn = lv_btn_create(lv_scr_act(), NULL);     /*Add a button the current screen*/
    lv_obj_set_pos(btn, 10, 10);                            /*Set its position*/
    lv_obj_set_size(btn, 120, 50);                          /*Set its size*/
    lv_obj_add_event_cb(btn, btn_event_cb, NULL);           /*Assign a callback to the button*/

    lv_obj_t * label = lv_label_create(btn, NULL);          /*Add a label to the button*/
    lv_label_set_text(label, "Button");                     /*Set the labels text*/
    lv_obj_align(label, NULL, LV_ALIGN_CENTER, 0, 0);
}

#endif