selectiontool.java

来自「开源（Open Source）项目JHotDraw的文档和源程序」· Java 代码 · 共 110 行

/*
 * @(#)SelectionTool.java 5.2
 *
 */

package CH.ifa.draw.standard;

import java.awt.*;
import java.awt.event.MouseEvent;
import java.util.Vector;
import CH.ifa.draw.framework.*;

/**
 * Tool to select and manipulate figures.
 * A selection tool is in one of three states, e.g., background
 * selection, figure selection, handle manipulation. The different
 * states are handled by different child tools.
 * <hr>
 * <b>Design Patterns</b><P>
 * <img src="images/red-ball-small.gif" width=6 height=6 alt=" o ">
 * <b><a href=../pattlets/sld032.htm>State</a></b><br>
 * SelectionTool is the StateContext and child is the State.
 * The SelectionTool delegates state specific
 * behavior to its current child tool.
 * <hr>
 */

public class SelectionTool extends AbstractTool {

    private Tool fChild = null;

    public SelectionTool(DrawingView view) {
        super(view);
    }

    /**
     * Handles mouse down events and starts the corresponding tracker.
     */
    public void mouseDown(MouseEvent e, int x, int y)
    {
        // on MS-Windows NT: AWT generates additional mouse down events
        // when the left button is down && right button is clicked.
        // To avoid dead locks we ignore such events
        if (fChild != null)
            return;

        view().freezeView();

        Handle handle = view().findHandle(e.getX(), e.getY());
        if (handle != null) {
            fChild = createHandleTracker(view(), handle);
        }
        else {
            Figure figure = drawing().findFigure(e.getX(), e.getY());
            if (figure != null) {
                fChild = createDragTracker(view(), figure);
            }
            else {
                if (!e.isShiftDown()) {
                    view().clearSelection();
                }
                fChild = createAreaTracker(view());
            }
        }
        fChild.mouseDown(e, x, y);
    }

    /**
     * Handles mouse drag events. The events are forwarded to the
     * current tracker.
     */
    public void mouseDrag(MouseEvent e, int x, int y) {
        if (fChild != null) // JDK1.1 doesn't guarantee mouseDown, mouseDrag, mouseUp
            fChild.mouseDrag(e, x, y);
    }

    /**
     * Handles mouse up events. The events are forwarded to the
     * current tracker.
     */
    public void mouseUp(MouseEvent e, int x, int y) {
        view().unfreezeView();
        if (fChild != null) // JDK1.1 doesn't guarantee mouseDown, mouseDrag, mouseUp
            fChild.mouseUp(e, x, y);
        fChild = null;
    }

    /**
     * Factory method to create a Handle tracker. It is used to track a handle.
     */
    protected Tool createHandleTracker(DrawingView view, Handle handle) {
        return new HandleTracker(view, handle);
    }

    /**
     * Factory method to create a Drag tracker. It is used to drag a figure.
     */
    protected Tool createDragTracker(DrawingView view, Figure f) {
        return new DragTracker(view, f);
    }

    /**
     * Factory method to create an area tracker. It is used to select an
     * area.
     */
    protected Tool createAreaTracker(DrawingView view) {
        return new SelectAreaTracker(view);
    }
}