basicdraggesturerecognizer.java

java jdk 1.4的源码

/*
 * @(#)BasicDragGestureRecognizer.java	1.5 03/01/23
 *
 * Copyright 2003 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */
package javax.swing.plaf.basic;

import java.awt.Toolkit;
import java.awt.event.*;
import javax.swing.*;
import sun.awt.dnd.SunDragSourceContextPeer;

/**
 * Default drag gesture recognition for drag operations performed by classses
 * that have a <code>dragEnabled</code> property.  The gesture for a drag in
 * this package is a mouse press over a selection followed by some movement
 * by enough pixels to keep it from being treated as a click.
 *
 * @author  Timothy Prinzing
 * @version 1.5 01/23/03
 */
class BasicDragGestureRecognizer implements MouseListener, MouseMotionListener {
    
    private MouseEvent dndArmedEvent = null;
    
    private static int motionThreshold;
    
    private static boolean checkedMotionThreshold = false;

    private static int getMotionThreshold() {
        if (checkedMotionThreshold) {
            return motionThreshold;
        } else {
            checkedMotionThreshold = true;
            try {
                motionThreshold = ((Integer)Toolkit.getDefaultToolkit().getDesktopProperty("DnD.gestureMotionThreshold")).intValue();
            } catch (Exception e) {
                motionThreshold = 5;
            }
        }
        return motionThreshold;
    }
    
    protected int mapDragOperationFromModifiers(MouseEvent e) {
        int mods = e.getModifiersEx();
        
        if ((mods & InputEvent.BUTTON1_DOWN_MASK) != InputEvent.BUTTON1_DOWN_MASK) {
            return TransferHandler.NONE;
        }

        JComponent c = getComponent(e);
        TransferHandler th = c.getTransferHandler();
        return SunDragSourceContextPeer.convertModifiersToDropAction(mods, th.getSourceActions(c)); 
    }
    
    public void mouseClicked(MouseEvent e) {
    }

    public void mousePressed(MouseEvent e) {
        dndArmedEvent = null;

	if (isDragPossible(e) && mapDragOperationFromModifiers(e) != TransferHandler.NONE) {
            dndArmedEvent = e;
	    e.consume();
	}
    }
    
    public void mouseReleased(MouseEvent e) {
        dndArmedEvent = null;
    }
    
    public void mouseEntered(MouseEvent e) {
        //dndArmedEvent = null;
    }
    
    public void mouseExited(MouseEvent e) {
        //if (dndArmedEvent != null && mapDragOperationFromModifiers(e) == TransferHandler.NONE) {
        //    dndArmedEvent = null;
        //}
    }

    public void mouseDragged(MouseEvent e) {
	if (dndArmedEvent != null) {
            e.consume();
            
            int action = mapDragOperationFromModifiers(e);
            
            if (action == TransferHandler.NONE) {
                return;
            }
            
	    int dx = Math.abs(e.getX() - dndArmedEvent.getX());
	    int dy = Math.abs(e.getY() - dndArmedEvent.getY());
            if ((dx > getMotionThreshold()) || (dy > getMotionThreshold())) {
		// start transfer... shouldn't be a click at this point
                JComponent c = getComponent(e);
		TransferHandler th = c.getTransferHandler();
		th.exportAsDrag(c, dndArmedEvent, action);
		dndArmedEvent = null;
	    }
	}
    }
    
    public void mouseMoved(MouseEvent e) {
    }
    
    private TransferHandler getTransferHandler(MouseEvent e) {
        JComponent c = getComponent(e);
        return c == null ? null : c.getTransferHandler();
    }
    
    /**
     * Determines if the following are true:
     * <ul>
     * <li>the press event is located over a selection
     * <li>the dragEnabled property is true
     * <li>A TranferHandler is installed
     * </ul>
     * <p>
     * This is implemented to check for a TransferHandler.
     * Subclasses should perform the remaining conditions.
     */
    protected boolean isDragPossible(MouseEvent e) {
        JComponent c = getComponent(e);
        return (c == null) ? true : (c.getTransferHandler() != null);
    }

    protected JComponent getComponent(MouseEvent e) {
	Object src = e.getSource();
	if (src instanceof JComponent) {
	    JComponent c = (JComponent) src;
	    return c;
	}
	return null;
    }

}