TrackingAdjustmentListener


1   /*
2    * Copyright 1999-2005 The Apache Software Foundation.
3    * 
4    * Licensed under the Apache License, Version 2.0 (the "License");
5    * you may not use this file except in compliance with the License.
6    * You may obtain a copy of the License at
7    * 
8    *      http://www.apache.org/licenses/LICENSE-2.0
9    * 
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS,
12   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13   * See the License for the specific language governing permissions and
14   * limitations under the License.
15   */
16  package org.apache.log4j.lf5.viewer;
17  
18  import java.awt.*;
19  import java.awt.event.AdjustmentEvent  ;
20  import java.awt.event.AdjustmentListener  ;
21  
22  /**
23   * An AdjustmentListener which ensures that an Adjustable (e.g. a Scrollbar)
24   * will "track" when the Adjustable expands.
25   * For example, when a vertical scroll bar is at its bottom anchor,
26   * the scrollbar will remain at the bottom.  When the vertical scroll bar
27   * is at any other location, then no tracking will happen.
28   * An instance of this class should only listen to one Adjustable as
29   * it retains state information about the Adjustable it listens to.
30   *
31   * @author Richard Wan
32   */
33  
34  // Contributed by ThoughtWorks Inc.
35  
36  public class TrackingAdjustmentListener implements AdjustmentListener   {
37    //--------------------------------------------------------------------------
38    //   Constants:
39    //--------------------------------------------------------------------------
40  
41    //--------------------------------------------------------------------------
42    //   Protected Variables:
43    //--------------------------------------------------------------------------
44  
45    protected int _lastMaximum = -1;
46  
47    //--------------------------------------------------------------------------
48    //   Private Variables:
49    //--------------------------------------------------------------------------
50  
51    //--------------------------------------------------------------------------
52    //   Constructors:
53    //--------------------------------------------------------------------------
54  
55    //--------------------------------------------------------------------------
56    //   Public Methods:
57    //--------------------------------------------------------------------------
58  
59    public void adjustmentValueChanged(AdjustmentEvent   e) {
60      Adjustable bar = e.getAdjustable();
61      int currentMaximum = bar.getMaximum();
62      if (bar.getMaximum() == _lastMaximum) {
63        return; // nothing to do, the adjustable has not expanded
64      }
65      int bottom = bar.getValue() + bar.getVisibleAmount();
66  
67      if (bottom + bar.getUnitIncrement() >= _lastMaximum) {
68        bar.setValue(bar.getMaximum()); // use the most recent maximum
69      }
70      _lastMaximum = currentMaximum;
71    }
72  
73    //--------------------------------------------------------------------------
74    //   Protected Methods:
75    //--------------------------------------------------------------------------
76  
77    //--------------------------------------------------------------------------
78    //   Private Methods:
79    //--------------------------------------------------------------------------
80  
81    //--------------------------------------------------------------------------
82    //   Nested Top-Level Classes or Interfaces
83    //--------------------------------------------------------------------------
84  }
85  
86
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