Image button has no LV_STATE_FOCUS in this state?

Applications
1

I create an image button like this:

    lv_obj_t* btn = lv_imgbtn_create(dlg);
    lv_obj_add_state(btn, LV_STATE_FOCUS_KEY);//It doesn't work？
    lv_obj_get_style_bg_opa(btn, 0);
    lv_imgbtn_set_src(btn, LV_IMGBTN_STATE_RELEASED, 0, "E:\\image\\os_win.png", 0);
    lv_obj_add_event_cb(btn, win_close_click_event_cb, LV_EVENT_CLICKED, NULL);
    lv_obj_set_size(btn, 256, 256);
    lv_obj_set_pos(btn, 10, 10);

I want the image button has keyborad focus state like lv_btn,what should I do?