我目前正在用Java编写一个简单的聊天，目前我仍然坚持这个问题： 我希望我的输出JTextPane的行为与您期望的良好聊天一样，即默认情况下，文本在新文本到达时自动滚动（使用outputfield.setCaretPosition（outputdocument.getLength（））），但是当用户向上滚动时当用户再次滚动到底部时，应该禁用并且当然会重新启用。
我尝试使用ScrollBars和所有，但我似乎无法找到一种方法来检测ScrollBar是否在底部。
我只是通过创建一个JTextPane，一个JScrollPane并将一个放到另一个中来创建可滚动的输出区域。
JTextPane outputpane = new JTextPane
...
JScrollPane outputscroll = new JScrollPane(outputpane);
outputscroll.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
编辑：这是我用来创建组件和显示新消息的代码：
// lots of imports
public class RoomFrame extends JFrame implements ListSelectionListener, ActionListener, Comparable, Runnable
{
public static final String DEFAULT_FONT = "Courier";
public static final int DEFAULT_FONT_SIZE = 12;
private JTextPane mOutputField;
private JScrollPane mOutputScroll;
private StyledDocument mOutputDocument;
public RoomFrame(...)
{
super(...);
createGUI();
setOutputStyles();
setVisible(true);
new Thread(this).start();
}
// ========================================================
private void createGUI()
{
Color borderhighlightouter = new Color(220, 220, 220);
Color borderhighlightinner = new Color(170, 170, 170);
Color bordershadowouter = new Color(120, 120, 120);
Color bordershadowinner = new Color(170, 170, 170);
setLayout(new GridBagLayout());
setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
setSize(500, 400);
// -----------------------------
// Output
mOutputField = new JTextPane();
mOutputField.setEditable(false);
mOutputField.setBackground(new Color(245, 245, 245));
mOutputDocument = mOutputField.getStyledDocument();
mOutputScroll = new JScrollPane(mOutputField);
mOutputScroll.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
mOutputScroll.setPreferredSize(new Dimension(250, 250));
mOutputScroll.setMinimumSize(new Dimension(50, 50));
mOutputScroll.setOpaque(false);
mOutputScroll.setBorder(BorderFactory.createCompoundBorder(BorderFactory.createEmptyBorder(0, 0, 1, 0), BorderFactory.createBevelBorder(BevelBorder.LOWERED, borderhighlightouter, borderhighlightinner, bordershadowouter, bordershadowinner)));
getContentPane().add(mOutputScroll);
}
private void setOutputStyles()
{
Style def = StyleContext.getDefaultStyleContext().getStyle(StyleContext.DEFAULT_STYLE);
Style regular = mOutputDocument.addStyle("regular", def);
StyleConstants.setFontFamily(def, DEFAULT_FONT);
StyleConstants.setFontSize(def, DEFAULT_FONT_SIZE);
StyleConstants.setFirstLineIndent(def, 100.0f);
Style nickname = mOutputDocument.addStyle("username", def);
StyleConstants.setBold(nickname, true);
StyleConstants.setForeground(nickname, new Color(50, 50, 220));
Style highlight = mOutputDocument.addStyle("highlight", def);
StyleConstants.setBold(highlight, true);
StyleConstants.setBackground(highlight, new Color(150, 0, 0));
Style join = mOutputDocument.addStyle("join", def);
StyleConstants.setBold(join, true);
StyleConstants.setForeground(join, new Color(20, 100, 20));
Style leave = mOutputDocument.addStyle("leave", def);
StyleConstants.setBold(leave, true);
StyleConstants.setForeground(leave, new Color(100, 100, 20));
Style topic = mOutputDocument.addStyle("topic", def);
StyleConstants.setBold(topic, true);
StyleConstants.setUnderline(topic, true);
Style error = mOutputDocument.addStyle("error", def);
StyleConstants.setBold(error, true);
StyleConstants.setForeground(error, new Color(255, 0, 0));
Style kick = mOutputDocument.addStyle("kick", def);
StyleConstants.setBold(kick, true);
StyleConstants.setForeground(kick, new Color(150, 0, 0));
}
private final boolean shouldScroll()
{
int min = mOutputScroll.getVerticalScrollBar().getValue() + mOutputScroll.getVerticalScrollBar().getVisibleAmount();
int max = mOutputScroll.getVerticalScrollBar().getMaximum();
return min == max;
}
// ========================================================
public void displayMessage(String message)
{
displayMessage(message, "");
}
public void displayMessage(String message, String style)
{
displayMessage(message, style, true);
}
public void displayMessage(String message, String style, boolean addnewline)
{
String newline = (addnewline ? "\n" : "");
style = (style.equals("") ? "regular" : style);
message = message.replace("\n", " ");
// check for highlight
try
{
mOutputDocument.insertString(mOutputDocument.getLength(),
String.format("%s%s", message, newline),
mOutputDocument.getStyle(style));
}
catch (Exception e) {}
// if (shouldScroll())
// mOutputField.setCaretPosition(mOutputDocument.getLength());
}
public void run()
{
while (true)
{
if (shouldScroll())
{
SwingUtilities.invokeLater(
new Runnable()
{
public void run()
{
mOutputScroll.getVerticalScrollBar().setValue(mOutputScroll.getVerticalScrollBar().getMaximum());
}
});
}
try { Thread.sleep(500); }
catch (InterruptedException e) { break; }
}
}
public void valueChanged(ListSelectionEvent event)
{
}
public void actionPerformed(ActionEvent event)
{
}
public final int compareTo(Object o) { return this.toString().compareTo(o.toString()); }
}
修改：感谢fireshadow52与another similar question的链接，我终于让它按照我想要的方式工作了：
private boolean isViewAtBottom()
{
JScrollBar sb = mOutputScroll.getVerticalScrollBar();
int min = sb.getValue() + sb.getVisibleAmount();
int max = sb.getMaximum();
System.out.println(min + " " + max);
return min == max;
}
private void scrollToBottom()
{
SwingUtilities.invokeLater(
new Runnable()
{
public void run()
{
mOutputScroll.getVerticalScrollBar().setValue(mOutputScroll.getVerticalScrollBar().getMaximum());
}
});
}
public void displayMessage(String message, String style, boolean prependnewline)
{
String newline = (prependnewline ? "\n" : "");
boolean scroll = isViewAtBottom() && prependnewline;
style = (style.equals("") ? "regular" : style);
message = message.replace("\n", " ");
try
{
mOutputDocument.insertString(mOutputDocument.getLength(),
String.format("%s%s", newline, message),
mOutputDocument.getStyle(style));
}
catch (Exception e) {}
if (scroll)
scrollToBottom();
}
再次感谢您的帮助！
答案 0 :(得分：2)
如果你只是想在底部滚动，那么这个应该帮助。
使用此方法检查滚动条是否在末尾（或底部），如果是，则使用setCaretPosition(Component.getDocument().getLength());自动向下滚动：
public boolean shouldScroll() {
int minimumValue = scrollPane.getVerticalScrollBar().getValue() + scrollPane.getVerticalScrollBar().getVisibleAmount();
int maximumValue = scrollPane.getVerticalScrollBar().getMaximum();
return maximumValue == minimumValue;
}
我在使用Google时发现了类似的结果，这使我得到了一个类似于按照要求运行的方法。
编辑：确保它在invokeLater()内完成，因为在滚动完成之前需要更新它。
我使用的完整示例：
public class ScrollTest extends Thread {
private JFrame frame;
private JTextArea textArea;
private JScrollPane scrollPane;
public static void main(String[] arguments) {
new ScrollTest().run();
}
public ScrollTest() {
textArea = new JTextArea(20, 20);
scrollPane = new JScrollPane(textArea);
frame = new JFrame("Test");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(scrollPane);
frame.pack();
frame.setVisible(true);
}
public void run() {
while (true) {
textArea.append("" + Math.random() + "\n");
if (shouldScroll()) {
SwingUtilities.invokeLater(new Runnable() {
@Override
public void run() {
scrollPane.getVerticalScrollBar().setValue(scrollPane.getVerticalScrollBar().getMaximum());
}
});
}
try {
Thread.sleep(500);
} catch (Exception exception) {
exception.printStackTrace();
}
}
}
public boolean shouldScroll() {
int minimumValue = scrollPane.getVerticalScrollBar().getValue() + scrollPane.getVerticalScrollBar().getVisibleAmount();
int maximumValue = scrollPane.getVerticalScrollBar().getMaximum();
return maximumValue == minimumValue;
}
}
答案 1 :(得分：1)
JScrollBar有getValue（）方法。只需在SwingUtilities.invokeLater（）中将其扭曲，即可在文本追加后调用。
答案 2 :(得分：1)
您可以使用AdjustmentListener来调整滚动条件，如example所示。