java - Java JTextPane + JScrollPane：取消/激活自动滚动

Question

我目前正在用 Java 编写一个简单的聊天，目前我被困在这个问题上：我希望我的输出 JTextPane 的行为就像你期望它从一个好的聊天中一样，即默认情况下，当新文本到达时文本会自动滚动（使用 outputfield.setCaretPosition(outputdocument.getLength()))，但是当用户向上滚动时，这应该被禁用，当然当用户再次滚动到底部时重新启用。

我试着玩弄 ScrollBars 和所有东西，但我似乎无法找到一种方法来检测 ScrollBar 是否在底部。

我只需创建一个 JTextPane、一个 JScrollPane 并将一个放入另一个中即可创建可滚动输出区域。

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()); }
}

编辑：感谢fireshadow52与另一个类似问题的链接，我终于让它完全按照我的意愿工作：

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();
}

再次感谢您的所有帮助！

score 2 · Accepted Answer

If you're only wanting to scroll when you're at the bottom then this should help.

Use this method to check and see if the scrollbar is at the end (or bottom), and if so, scroll down automatically using setCaretPosition(Component.getDocument().getLength());:

public boolean shouldScroll() {
    int minimumValue = scrollPane.getVerticalScrollBar().getValue() + scrollPane.getVerticalScrollBar().getVisibleAmount();
    int maximumValue = scrollPane.getVerticalScrollBar().getMaximum();
    return maximumValue == minimumValue;
}

I found similar results when using Google which led me to a method similar to this one which worked as requested.

Edit: Make sure that it is done within invokeLater() as it needs to be updated before scrolling is done.

A full example of what I use:

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;
    }

}

score 1 · Accepted Answer

JScrollBar 有 getValue() 方法。只需在 SwingUtilities.invokeLater() 中对其进行变形，以便在文本附加后调用。

score 1 · Accepted Answer

1

您可以使用AdjustmentListener条件滚动，如本示例所示。

于 2012-01-09T15:16:13.677 回答

java - Java JTextPane + JScrollPane：取消/激活自动滚动

3 回答 3

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