com.tascape.reactor.ui.SmartScroller Maven / Gradle / Ivy
/*
* Copyright 2015- 2016 Nebula Bay.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.tascape.reactor.ui;
import java.awt.Component;
import java.awt.event.AdjustmentEvent;
import java.awt.event.AdjustmentListener;
import javax.swing.BoundedRangeModel;
import javax.swing.JScrollBar;
import javax.swing.JScrollPane;
import javax.swing.SwingUtilities;
import javax.swing.text.DefaultCaret;
import javax.swing.text.JTextComponent;
/**
* The SmartScroller will attempt to keep the viewport positioned based on
* the users interaction with the scrollbar. The normal behaviour is to keep
* the viewport positioned to see new data as it is dynamically added.
* https://tips4java.wordpress.com/2013/03/03/smart-scrolling/
*
* Assuming vertical scrolling and data is added to the bottom:
*
* - when the viewport is at the bottom and new data is added,
* then automatically scroll the viewport to the bottom
* - when the viewport is not at the bottom and new data is added,
* then do nothing with the viewport
*
* Assuming vertical scrolling and data is added to the top:
*
* - when the viewport is at the top and new data is added,
* then do nothing with the viewport
* - when the viewport is not at the top and new data is added, then adjust
* the viewport to the relative position it was at before the data was added
*
* Similiar logic would apply for horizontal scrolling.
*/
public class SmartScroller implements AdjustmentListener {
public static final int HORIZONTAL = 0;
public static final int VERTICAL = 1;
public static final int START = 0;
public static final int END = 1;
private int viewportPosition;
private JScrollBar scrollBar;
private boolean adjustScrollBar = true;
private int previousValue = -1;
private int previousMaximum = -1;
/**
* Convenience constructor.
* Scroll direction is VERTICAL and viewport position is at the END.
*
* @param scrollPane the scroll pane to monitor
*/
public SmartScroller(JScrollPane scrollPane) {
this(scrollPane, VERTICAL, END);
}
/**
* Convenience constructor.
* Scroll direction is VERTICAL.
*
* @param scrollPane the scroll pane to monitor
* @param viewportPosition valid values are START and END
*/
public SmartScroller(JScrollPane scrollPane, int viewportPosition) {
this(scrollPane, VERTICAL, viewportPosition);
}
/**
* Specify how the SmartScroller will function.
*
* @param scrollPane the scroll pane to monitor
* @param scrollDirection indicates which JScrollBar to monitor.
* Valid values are HORIZONTAL and VERTICAL.
* @param viewportPosition indicates where the viewport will normally be
* positioned as data is added.
* Valid values are START and END
*/
public SmartScroller(JScrollPane scrollPane, int scrollDirection, int viewportPosition) {
if (scrollDirection != HORIZONTAL && scrollDirection != VERTICAL) {
throw new IllegalArgumentException("invalid scroll direction specified");
}
if (viewportPosition != START && viewportPosition != END) {
throw new IllegalArgumentException("invalid viewport position specified");
}
this.viewportPosition = viewportPosition;
if (scrollDirection == HORIZONTAL) {
scrollBar = scrollPane.getHorizontalScrollBar();
} else {
scrollBar = scrollPane.getVerticalScrollBar();
}
scrollBar.addAdjustmentListener(this);
// Turn off automatic scrolling for text components
Component view = scrollPane.getViewport().getView();
if (view instanceof JTextComponent) {
JTextComponent textComponent = (JTextComponent) view;
DefaultCaret caret = (DefaultCaret) textComponent.getCaret();
caret.setUpdatePolicy(DefaultCaret.NEVER_UPDATE);
}
}
@Override
public void adjustmentValueChanged(final AdjustmentEvent e) {
SwingUtilities.invokeLater(() -> {
checkScrollBar(e);
});
}
/*
* Analyze every adjustment event to determine when the viewport
* needs to be repositioned.
*/
private void checkScrollBar(AdjustmentEvent e) {
// The scroll bar listModel contains information needed to determine
// whether the viewport should be repositioned or not.
JScrollBar jsb = (JScrollBar) e.getSource();
BoundedRangeModel listModel = jsb.getModel();
int value = listModel.getValue();
int extent = listModel.getExtent();
int maximum = listModel.getMaximum();
boolean valueChanged = previousValue != value;
boolean maximumChanged = previousMaximum != maximum;
// Check if the user has manually repositioned the scrollbar
if (valueChanged && !maximumChanged) {
if (viewportPosition == START) {
adjustScrollBar = value != 0;
} else {
adjustScrollBar = value + extent >= maximum;
}
}
// Reset the "value" so we can reposition the viewport and
// distinguish between a user scroll and a program scroll.
// (ie. valueChanged will be false on a program scroll)
if (adjustScrollBar && viewportPosition == END) {
// Scroll the viewport to the end.
jsb.removeAdjustmentListener(this);
value = maximum - extent;
jsb.setValue(value);
jsb.addAdjustmentListener(this);
}
if (adjustScrollBar && viewportPosition == START) {
// Keep the viewport at the same relative viewportPosition
jsb.removeAdjustmentListener(this);
value = value + maximum - previousMaximum;
jsb.setValue(value);
jsb.addAdjustmentListener(this);
}
previousValue = value;
previousMaximum = maximum;
}
}