// Adds event listener

    /** Adds a event listener for a specified event with the priority of scene graph.

     *  @param listener The listener of a specified event.

     *  @param node The priority of the listener is based on the draw order of this node.

     *  @note  The priority of scene graph will be fixed value 0. So the order of listener item

     *          in the vector will be ‘ <0, scene graph (0 priority), >0‘.

     */

    void addEventListenerWithSceneGraphPriority(EventListener* listener, Node* node);

    /** Adds a event listener for a specified event with the fixed priority.

     *  @param listener The listener of a specified event.

     *  @param fixedPriority The fixed priority of the listener.

     *  @note A lower priority will be called before the ones that have a higher value.

     *        0 priority is forbidden for fixed priority since it‘s used for scene graph based priority.

     */

    void addEventListenerWithFixedPriority(EventListener* listener, int fixedPriority);