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