鼠标滚轮事件onGenericMotionEvent(MotionEvent event)

1.在View或者Activity重写onGernericMotionEvent方法，能监听鼠标或者其它外接设备的事件，例如

    @Override
    public boolean onGenericMotionEvent(MotionEvent event) {
        if ((event.getSource() & InputDevice.SOURCE_CLASS_POINTER) != 0) {
            switch (event.getAction()) {
                case MotionEvent.ACTION_SCROLL: {
                    // Handle mouse (or ext. device) by shifting the page depending on the scroll
                    final float vscroll;
                    final float hscroll;
                    if ((event.getMetaState() & KeyEvent.META_SHIFT_ON) != 0) {
                        vscroll = 0;
                        hscroll = event.getAxisValue(MotionEvent.AXIS_VSCROLL);
                    } else {
                        vscroll = -event.getAxisValue(MotionEvent.AXIS_VSCROLL);
                        hscroll = event.getAxisValue(MotionEvent.AXIS_HSCROLL);
                    }
                    if (hscroll != 0 || vscroll != 0) {
                        boolean isForwardScroll = mIsRtl ? (hscroll < 0 || vscroll < 0)
                                                         : (hscroll > 0 || vscroll > 0);
                        if (isForwardScroll) {
                            scrollRight();
                        } else {
                            scrollLeft();
                        }
                        return true;
                    }
                }
            }
        }
        return super.onGenericMotionEvent(event);
    }