1/*
2 * Copyright (c) 2005, 2008, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.  Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25package javax.swing.plaf.basic;
26
27import java.awt.Toolkit;
28import java.awt.event.*;
29import java.awt.dnd.DragSource;
30import javax.swing.*;
31import sun.awt.dnd.SunDragSourceContextPeer;
32import sun.awt.AppContext;
33
34/**
35 * Drag gesture recognition support for classes that have a
36 * <code>TransferHandler</code>. The gesture for a drag in this class is a mouse
37 * press followed by movement by <code>DragSource.getDragThreshold()</code>
38 * pixels. An instance of this class is maintained per AppContext, and the
39 * public static methods call into the appropriate instance.
40 *
41 * @author Shannon Hickey
42 */
43class DragRecognitionSupport {
44    private int motionThreshold;
45    private MouseEvent dndArmedEvent;
46    private JComponent component;
47
48    /**
49     * This interface allows us to pass in a handler to mouseDragged,
50     * so that we can be notified immediately before a drag begins.
51     */
52    public static interface BeforeDrag {
53        public void dragStarting(MouseEvent me);
54    }
55
56    /**
57     * Returns the DragRecognitionSupport for the caller's AppContext.
58     */
59    private static DragRecognitionSupport getDragRecognitionSupport() {
60        DragRecognitionSupport support =
61            (DragRecognitionSupport)AppContext.getAppContext().
62                get(DragRecognitionSupport.class);
63
64        if (support == null) {
65            support = new DragRecognitionSupport();
66            AppContext.getAppContext().put(DragRecognitionSupport.class, support);
67        }
68
69        return support;
70    }
71
72    /**
73     * Returns whether or not the event is potentially part of a drag sequence.
74     */
75    public static boolean mousePressed(MouseEvent me) {
76        return getDragRecognitionSupport().mousePressedImpl(me);
77    }
78
79    /**
80     * If a dnd recognition has been going on, return the MouseEvent
81     * that started the recognition. Otherwise, return null.
82     */
83    public static MouseEvent mouseReleased(MouseEvent me) {
84        return getDragRecognitionSupport().mouseReleasedImpl(me);
85    }
86
87    /**
88     * Returns whether or not a drag gesture recognition is ongoing.
89     */
90    public static boolean mouseDragged(MouseEvent me, BeforeDrag bd) {
91        return getDragRecognitionSupport().mouseDraggedImpl(me, bd);
92    }
93
94    private void clearState() {
95        dndArmedEvent = null;
96        component = null;
97    }
98
99    private int mapDragOperationFromModifiers(MouseEvent me,
100                                              TransferHandler th) {
101
102        if (th == null || !SwingUtilities.isLeftMouseButton(me)) {
103            return TransferHandler.NONE;
104        }
105
106        return SunDragSourceContextPeer.
107            convertModifiersToDropAction(me.getModifiersEx(),
108                                         th.getSourceActions(component));
109    }
110
111    /**
112     * Returns whether or not the event is potentially part of a drag sequence.
113     */
114    private boolean mousePressedImpl(MouseEvent me) {
115        component = (JComponent)me.getSource();
116
117        if (mapDragOperationFromModifiers(me, component.getTransferHandler())
118                != TransferHandler.NONE) {
119
120            motionThreshold = DragSource.getDragThreshold();
121            dndArmedEvent = me;
122            return true;
123        }
124
125        clearState();
126        return false;
127    }
128
129    /**
130     * If a dnd recognition has been going on, return the MouseEvent
131     * that started the recognition. Otherwise, return null.
132     */
133    private MouseEvent mouseReleasedImpl(MouseEvent me) {
134        /* no recognition has been going on */
135        if (dndArmedEvent == null) {
136            return null;
137        }
138
139        MouseEvent retEvent = null;
140
141        if (me.getSource() == component) {
142            retEvent = dndArmedEvent;
143        } // else component has changed unexpectedly, so return null
144
145        clearState();
146        return retEvent;
147    }
148
149    /**
150     * Returns whether or not a drag gesture recognition is ongoing.
151     */
152    private boolean mouseDraggedImpl(MouseEvent me, BeforeDrag bd) {
153        /* no recognition is in progress */
154        if (dndArmedEvent == null) {
155            return false;
156        }
157
158        /* component has changed unexpectedly, so bail */
159        if (me.getSource() != component) {
160            clearState();
161            return false;
162        }
163
164        int dx = Math.abs(me.getX() - dndArmedEvent.getX());
165        int dy = Math.abs(me.getY() - dndArmedEvent.getY());
166        if ((dx > motionThreshold) || (dy > motionThreshold)) {
167            TransferHandler th = component.getTransferHandler();
168            int action = mapDragOperationFromModifiers(me, th);
169            if (action != TransferHandler.NONE) {
170                /* notify the BeforeDrag instance */
171                if (bd != null) {
172                    bd.dragStarting(dndArmedEvent);
173                }
174                th.exportAsDrag(component, dndArmedEvent, action);
175                clearState();
176            }
177        }
178
179        return true;
180    }
181}
182