lvgl按键抬起完成切屏显示例程

以下是一个基于LVGL的按键抬起完成切屏显示的例程：

#include <lvgl.h>

#define LV_EXAMPLE_KEYPAD_BTN_CNT (5)

lv_obj_t * screen1;
lv_obj_t * screen2;
lv_obj_t * keypad;
lv_obj_t * btns[LV_EXAMPLE_KEYPAD_BTN_CNT];

static void btn_event_cb(lv_obj_t * obj, lv_event_t event)
{
    if(event == LV_EVENT_RELEASED) {
        if(obj == btns[0]) {
            lv_scr_load(screen1);
        } else if(obj == btns[1]) {
            lv_scr_load(screen2);
        }
    }
}

void lv_example_keypad_1(void)
{
    /* Create screen1 */
    screen1 = lv_obj_create(NULL, NULL);
    lv_scr_load(screen1);

    /* Create a label on screen1 */
    lv_obj_t * label1 = lv_label_create(screen1, NULL);
    lv_label_set_text(label1, "Screen 1");

    /* Create screen2 */
    screen2 = lv_obj_create(NULL, NULL);

    /* Create a label on screen2 */
    lv_obj_t * label2 = lv_label_create(screen2, NULL);
    lv_label_set_text(label2, "Screen 2");

    /* Create a keypad */
    keypad = lv_obj_create(NULL, NULL);
    lv_obj_set_size(keypad, 200, 150);
    lv_obj_center(keypad);

    /* Create buttons on the keypad */
    btns[0] = lv_btn_create(keypad, NULL);
    lv_obj_set_size(btns[0], 60, 60);
    lv_btn_set_fit2(btns[0], LV_FIT_NONE, LV_FIT_TIGHT);
    lv_obj_align(btns[0], NULL, LV_ALIGN_IN_TOP_LEFT, 20, 20);
    lv_obj_t * label3 = lv_label_create(btns[0], NULL);
    lv_label_set_text(label3, "Screen 1");

    btns[1] = lv_btn_create(keypad, btns[0]);
    lv_obj_align(btns[1], btns[0], LV_ALIGN_OUT_RIGHT_MID, 20, 0);
    lv_obj_t * label4 = lv_label_create(btns[1], NULL);
    lv_label_set_text(label4, "Screen 2");

    /* Set button event callbacks */
    lv_obj_set_event_cb(btns[0], btn_event_cb);
    lv_obj_set_event_cb(btns[1], btn_event_cb);
}

该示例中创建了两个屏幕(screen1和screen2)，以及一个包含两个按钮的键盘(keypad)。按下按钮时，会切换到相应的屏幕。

要实现按键抬起完成切屏显示，需要在按钮的回调函数中判断事件类型是否为LV_EVENT_RELEASED，如果是则执行相应的屏幕加载操作。在该示例中，使用lv_scr_load()函数来加载屏幕。