我正在尝试模仿Adium和我见过的大多数其他聊天客户端的功能，其中当新邮件进入时滚动条会向前移动，但前提是你已经在那里。换句话说，如果您向上滚动了几行并正在阅读，当有新消息进入时它不会将您的位置跳到屏幕底部;这会很烦人。但如果您滚动到底部，程序会正确地假设您希望始终查看最新的消息，因此会相应地自动滚动。
我有一段时间试图模仿这个;该平台似乎不惜一切代价来对抗这种行为。我能做的最好的事情如下：
在构造函数中：
JTextArea chatArea = new JTextArea();
JScrollPane chatAreaScrollPane = new JScrollPane(chatArea);
// We will manually handle advancing chat window
DefaultCaret caret = (DefaultCaret) chatArea.getCaret();
caret.setUpdatePolicy(DefaultCaret.NEVER_UPDATE);
处理新文本的方法：
boolean atBottom = isViewAtBottom();
// Append the text using styles etc to the chatArea
if (atBottom) {
scrollViewportToBottom();
}
public boolean isAtBottom() {
// Is the last line of text the last line of text visible?
Adjustable sb = chatAreaScrollPane.getVerticalScrollBar();
int val = sb.getValue();
int lowest = val + sb.getVisibleAmount();
int maxVal = sb.getMaximum();
boolean atBottom = maxVal == lowest;
return atBottom;
}
private void scrollToBottom() {
chatArea.setCaretPosition(chatArea.getDocument().getLength());
}
现在，这种方法有效，但由于两个原因，它很笨拙而不理想。
在你问之前，是的，我已经在Text Area Scrolling上阅读了这篇博客文章，但默认滚动到最低行为不是我想要的。
其他相关（但在我看来，在这方面并不完全有用）问题： Setting scroll bar on a jscrollpane Making a JScrollPane automatically scroll all the way down.
非常感谢这方面的任何帮助。
编辑：
根据Devon_C_Miller的建议，我有一种改进的滚动方式，解决问题＃1。
private void scrollToBottom() {
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
try {
int endPosition = chatArea.getDocument().getLength();
Rectangle bottom = chatArea.modelToView(endPosition);
chatArea.scrollRectToVisible(bottom);
}
catch (BadLocationException e) {
System.err.println("Could not scroll to " + e);
}
}
});
}
我仍有问题＃2。
答案 0 :(得分：6)
查看scrollRectToVisible(Rectangle r)和modelToView(int pos)
这应该可以在不影响用户选择的情况下为您提供所需的信息。
对于滚动条，尝试强制滚动并在不同事件上发生追加。例如：
if (atBottom) {
// append new line & do scroll
SwingUtilities.invokerLater(new Runnable(){
public void run() {
// append text
}});
} else {
// append newline
// append text
}
答案 1 :(得分：3)
基于之前的答案和进一步的Google，我做了一个测试，其中一个Thread继续将字符串附加到JScrollPane中的JTextArea。我认为在这里使用invokeLater很重要，因为在滚动到该值之前，需要使用新的最大值更新JScrollBar。使用invokeLater，AWT Thread将处理这个问题。
private class AppendThread extends Thread {
public void run() {
while (true) {
String s = "random number = " + Math.random() + "\n";
boolean scrollDown = textAreaBottomIsVisible();
textArea.append(s);
if (scrollDown) {
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
JScrollBar bar = scrollPane.getVerticalScrollBar();
bar.setValue(bar.getMaximum());
}
}
);
}
try {
Thread.sleep(1000);
} catch (Exception e) {
System.err.println("exception = " + e);
}
}
}
private boolean textAreaBottomIsVisible() {
Adjustable sb = scrollPane.getVerticalScrollBar();
int val = sb.getValue();
int lowest = val + sb.getVisibleAmount();
int maxVal = sb.getMaximum();
boolean atBottom = maxVal == lowest;
return atBottom;
}
}
答案 2 :(得分：1)
答案 3 :(得分：1)
我花了最近几天尝试不同的方法解决这个问题。我发现的最佳解决方案是替换JScrollPane视口的布局管理器，并在那里实现所有需要的滚动行为。跳跃的滚动条旋钮消失了，而且速度非常快 - 它创造了另一种竞争条件我不得不解决。详细信息如下：http://www.java-forums.org/awt-swing/56808-scroll-bar-knob-jumpy-when-component-growing.html
答案 4 :(得分：1)
有点晚了，但我找到的是http://www.camick.com/java/source/SmartScroller.java
实质上，您可以使用以下代码：
JScrollPane scrollPane = new JScrollPane(myOversizedComponent);
// Injects smartscroll behaviour to your scrollpane
new SmartScroller(scrollPane);
这里是SmartScroller类：
import java.awt.Component;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.text.*;
/**
* 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.
*
* 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 final static int HORIZONTAL = 0;
public final static int VERTICAL = 1;
public final static int START = 0;
public final static 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(new Runnable()
{
public void run()
{
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 scrollBar = (JScrollBar)e.getSource();
BoundedRangeModel listModel = scrollBar.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.
scrollBar.removeAdjustmentListener( this );
value = maximum - extent;
scrollBar.setValue( value );
scrollBar.addAdjustmentListener( this );
}
if (adjustScrollBar && viewportPosition == START)
{
// Keep the viewport at the same relative viewportPosition
scrollBar.removeAdjustmentListener( this );
value = value + maximum - previousMaximum;
scrollBar.setValue( value );
scrollBar.addAdjustmentListener( this );
}
previousValue = value;
previousMaximum = maximum;
}
}
答案 5 :(得分：0)
public static void scrollToBottom(JComponent component)
{
Rectangle visibleRect = component.getVisibleRect();
visibleRect.y = component.getHeight() - visibleRect.height;
component.scrollRectToVisible(visibleRect);
}
您可以在此处找到完整的详细信息：How to make JTextPane autoscroll only when scroll bar is at bottom and scroll lock is off?
答案 6 :(得分：0)
DefaultCaret caret = (DefaultCaret)textArea.getCaret();
caret.setUpdatePolicy(DefaultCaret.ALWAYS_UPDATE);