001/* 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017package org.apache.log4j.lf5.viewer; 018 019import java.awt.Adjustable; 020import java.awt.event.AdjustmentEvent; 021import java.awt.event.AdjustmentListener; 022 023/** 024 * An AdjustmentListener which ensures that an Adjustable (e.g. a Scrollbar) 025 * will "track" when the Adjustable expands. 026 * For example, when a vertical scroll bar is at its bottom anchor, 027 * the scrollbar will remain at the bottom. When the vertical scroll bar 028 * is at any other location, then no tracking will happen. 029 * An instance of this class should only listen to one Adjustable as 030 * it retains state information about the Adjustable it listens to. 031 * 032 * @author Richard Wan 033 */ 034 035// Contributed by ThoughtWorks Inc. 036 037public class TrackingAdjustmentListener implements AdjustmentListener { 038 //-------------------------------------------------------------------------- 039 // Constants: 040 //-------------------------------------------------------------------------- 041 042 //-------------------------------------------------------------------------- 043 // Protected Variables: 044 //-------------------------------------------------------------------------- 045 046 protected int _lastMaximum = -1; 047 048 //-------------------------------------------------------------------------- 049 // Private Variables: 050 //-------------------------------------------------------------------------- 051 052 //-------------------------------------------------------------------------- 053 // Constructors: 054 //-------------------------------------------------------------------------- 055 056 //-------------------------------------------------------------------------- 057 // Public Methods: 058 //-------------------------------------------------------------------------- 059 060 public void adjustmentValueChanged(AdjustmentEvent e) { 061 Adjustable bar = e.getAdjustable(); 062 int currentMaximum = bar.getMaximum(); 063 if (bar.getMaximum() == _lastMaximum) { 064 return; // nothing to do, the adjustable has not expanded 065 } 066 int bottom = bar.getValue() + bar.getVisibleAmount(); 067 068 if (bottom + bar.getUnitIncrement() >= _lastMaximum) { 069 bar.setValue(bar.getMaximum()); // use the most recent maximum 070 } 071 _lastMaximum = currentMaximum; 072 } 073 074 //-------------------------------------------------------------------------- 075 // Protected Methods: 076 //-------------------------------------------------------------------------- 077 078 //-------------------------------------------------------------------------- 079 // Private Methods: 080 //-------------------------------------------------------------------------- 081 082 //-------------------------------------------------------------------------- 083 // Nested Top-Level Classes or Interfaces 084 //-------------------------------------------------------------------------- 085} 086