RCP学习：GEF编辑器的鼠标的hover policy以及一个预览窗口效果

    /**
     * Creates the initial EditPolicies and/or reserves slots for dynamic ones.
     * Should be implemented to install the inital EditPolicies based on the
     * model's initial state. <code>null</code> can be used to reserve a "slot",
     * should there be some desire to guarantee the ordering of EditPolcies.
     * 
     * @see EditPart#installEditPolicy(Object, EditPolicy)
     */
    protected abstract void createEditPolicies();

/**
 * 
 * @author caiyu
 * 
 */
public abstract class CommonHoverEditPolicy extends GraphicalEditPolicy {
    public static final String ROLE = "CommonLineAssistantEditPolicy";

    protected IFigure handleLayer;
    /* the List of handles */
    protected List<Handle> handles;

    /* the Hover Listener */
    private MouseMotionListener hoverListener;

    /* listener for every handle */
    private MouseMotionListener handleListener;

    private LayoutListener removeListener;

    private Timer timer;

    private boolean hovering = false;

    protected int TIME_INTERVAL = 1000;

　　 public void activate() {
        super.activate();
        addHoverListener();
        addHandleListener();
    }

    private void addHandleListener() {
        handleListener = new MouseMotionListener() {

            public void mouseDragged(MouseEvent me) {
            }

            public void mouseEntered(MouseEvent me) {

            }

            public void mouseExited(MouseEvent me) {
                cancelTimer();
                startTimer();
            }

            public void mouseHover(MouseEvent me) {
            }

            public void mouseMoved(MouseEvent me) {

            }
        };
    }

    protected void addHoverListener() {
        final IFigure figure = getHostFigure();
        hoverListener = new MouseMotionListener() {
            public void mouseDragged(MouseEvent me) {
            }

            public void mouseEntered(MouseEvent me) {

            }

            public void mouseExited(MouseEvent me) {
                startTimer();
            }

            public void mouseHover(MouseEvent me) {
                cancelTimer();
                addHoverHandles();
                hovering = true;
            }

            public void mouseMoved(MouseEvent me) {
            }
        };
        /**
         * 被删除的时候清除监听
         */
        removeListener = new LayoutListener() {
            @Override
            public void invalidate(IFigure container) {
            }

            @Override
            public boolean layout(IFigure container) {
                return false;
            }

            @Override
            public void postLayout(IFigure container) {
            }

            @Override
            public void remove(IFigure child) {
                if (child == figure) {
                    clearHoverHandles();
                    cancelTimer();
                    figure.getParent().removeLayoutListener(removeListener);
                }
            }

            @Override
            public void setConstraint(IFigure child, Object constraint) {
            }
        };

        if (figure != null) {
            figure.addMouseMotionListener(hoverListener);
            if (figure.getParent() != null)
                figure.getParent().addLayoutListener(removeListener);
        }
    }

    /**
     * Adds the handles to the handle layer.
     */
    protected void addHoverHandles() {
        clearHoverHandles();
        handleLayer = getLayer(LayerConstants.HANDLE_LAYER);
        handles = createHoverHandles();
        for (int i = 0; i < handles.size(); i++) {
            IFigure handle = (IFigure) handles.get(i);
            handleLayer.add(handle);
            handle.addMouseMotionListener(handleListener);
        }
    }

    protected void clearHoverHandles() {
        if (handles == null)
            return;
        if (handleLayer == null)
            handleLayer = getLayer(LayerConstants.HANDLE_LAYER);
        for (int i = 0; i < handles.size(); i++) {
            IFigure handle = (IFigure) handles.get(i);
            try {
                handleLayer.remove(handle);
            } catch (Exception e) {
                e.printStackTrace();
            }
            if (handleListener != null)
                handle.removeMouseMotionListener(handleListener);
        }
        handles = null;
    }

    protected void cancelTimer() {
        if (timer != null) {
            timer.cancel();
        }
    }

    protected void startTimer() {
        if (!hovering)
            return;

        if (timer != null) {
            timer.cancel();
        }

        timer = new Timer(true);
        timer.schedule(new TimerTask() {
            public void run() {
                Display.getDefault().syncExec(new Runnable() {
                    public void run() {
                        clearHoverHandles();
                    }
                });
            }
        }, TIME_INTERVAL);
    }

    protected abstract List<Handle> createHoverHandles();
}