LVGL V8之Button

在当前活动界面创建一个Button

• lv_scr_act()获取当前活动界面，作为parent窗口参数传入lv_btn_create，返回一个创建好的Button指针

 lv_obj_t* btn = lv_btn_create(lv_scr_act());

• 设置窗口位置，将Button位置设置在当前界面的x为100，y为30处

 lv_obj_set_pos(btn, 100, 30);

• 将Button宽度设置为220，高度设置为50

lv_obj_set_size(btn, 220, 50);

• 在Button上创建个Label

 lv_obj_t* label = lv_label_create(btn);

• 设置Label名称为Button

 lv_label_set_text(label, "Button");

• 使用 lv_obj_center函数使Button字居中显示

  lv_obj_center(label);

Button事件回调处理

• 回调函数中获取到点击目标的事件类型lv_event_code_t

static void btn_event_cb(lv_event_t* e)
{
    lv_event_code_t code = (lv_event_code_t)lv_event_get_code(e); 
}

• 获取被点击的目标对象

lv_obj_t* btn = lv_event_get_target(e);

• 仅对LV_EVENT_CLICKED事件进行处理

 if (code == LV_EVENT_CLICKED) {
 }

• 获取被点击对象的第一个子对象

 lv_obj_t* label = lv_obj_get_child(btn, 0);

• 修改第一个子对象的内容

  static uint8_t cnt = 0;
  cnt++;
  lv_label_set_text_fmt(label, "Button: %d", cnt);

完整实例代码，仅供参考

static void btn_event_cb(lv_event_t* e)
{
    lv_event_code_t code = (lv_event_code_t)lv_event_get_code(e);
    lv_obj_t* btn = lv_event_get_target(e);
    if (code == 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);
    }
}

static void lv_example_get_started_1(void)
{
    lv_obj_t* btn = lv_btn_create(lv_scr_act());
    lv_obj_set_pos(btn, 100, 30);
    lv_obj_set_size(btn, 220, 50);
    lv_obj_add_event_cb(btn, btn_event_cb, LV_EVENT_ALL, NULL);

    lv_obj_t* label = lv_label_create(btn);
    lv_label_set_text(label, "Button");
    lv_obj_center(label);
}

调用lv_example_get_started_1后的操作效果

仅注册LV_EVENT_CLICKED

 lv_obj_add_event_cb(btn, btn_event_cb, LV_EVENT_CLICKED, NULL);

 - 则处理函数中可以不需要if判断事件

static void btn_event_cb(lv_event_t* e)
{
    lv_obj_t* btn = lv_event_get_target(e);
        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);  
}

使用LV_USE_USER_DATA方式传递label对象

 lv_obj_add_event_cb(btn, btn_event_cb, LV_EVENT_CLICKED, label);

• 点击事件中使用lv_event_get_user_data函数获取label对象

static void btn_event_cb(lv_event_t* e)
{
        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_t*)lv_event_get_user_data(e);
        lv_label_set_text_fmt(label, "Button: %d", cnt);   
}