如果单单的调用点击的方法，按钮被点击的效果是不会被看到的。

private void OnGUI()
{
    if (GUILayout.Button("Button Click")) {
        // ExecuteEvents.Execute<IPointerClickHandler>(button.gameObject, new PointerEventData(EventSystem.current), ExecuteEvents.pointerClickHandler);
        //会有按钮点击的效果出现
        ExecuteEvents.Execute<ISubmitHandler>(button.gameObject , 
        new PointerEventData(EventSystem.current), ExecuteEvents.submitHandler);
    }

    if (GUILayout.Button("Image Click")) {
        //单单就是触发点击事件，添加了EventTrigger的Image
        ExecuteEvents.Execute<IPointerClickHandler>(img.gameObject , 
        new PointerEventData(EventSystem.current), ExecuteEvents.pointerClickHandler);
    }
}

ExecuteEvents等类都是在UnityEngine.EventSystems命名空间中