U3D 精灵的点击监听

    void OnMouseDown() {
        print("鼠标按下了");
    }

OnMouseDown    OnMouseDown is called when the user has pressed the mouse button while over the GUIElement or Collider.
OnMouseDrag    OnMouseDrag is called when the user has clicked on a GUIElement or Collider and is still holding down the mouse.
OnMouseEnter    Called when the mouse enters the GUIElement or Collider.
OnMouseExit    Called when the mouse is not any longer over the GUIElement or Collider.
OnMouseOver    Called every frame while the mouse is over the GUIElement or Collider.
OnMouseUp    OnMouseUp is called when the user has released the mouse button.
OnMouseUpAsButton