java - JScrollPane:重新验证后滚动位置

Question

我的问题与这个非常相似:

Set the vertical scroll to current position after revalidate

不同之处在于，我不想滚动回 0，而是滚动到更新子组件之前保存的位置，如下所示:

final int oldPos = scrollPanel.getVerticalScrollBar().getValue();
removeAll(); // Removes all components from the JPanel
add(mList()); // Adds a bunch of content
revalidate();
SwingUtilities.invokeLater(new Runnable()
{
    @Override
    public void run()
    {
        ml.getVerticalScrollBar().setValue(oldPos);
    }
});

此代码在另一个组件的鼠标运动监听器中触发，因此调用非常频繁。

即使最初 jscrollpane 滚动到顶部，有时 oldPos 也不为零，这会导致 Pane 向下滚动，尽管设置了该值。

即使我强制滚动到顶部并只记录 oldPos 值，它也不总是 0:

final int oldPos = scrollPanel.getVerticalScrollBar().getValue();
removeAll();
add(mList());
revalidate();
SwingUtilities.invokeLater(new Runnable()
{
    @Override
    public void run()
    {
        System.out.println(oldPos); // Sometimes this is > 2000
        ml.getVerticalScrollBar().setValue(0); // scroll to the top
    }
});

我猜如果 oldPos = ... 代码在调用前一个执行的 invokeLater block 之前执行，就会发生这种情况。我该如何解决这个问题？

更新:

我按照 @mKorbel 的建议创建了一个 sscce:

更新 2: 我更新了 sscce 以允许在 jTextArea/jLabel 之间切换，启用/禁用监听器的重新绑定(bind)，以及在 jTextArea 和继承自 jTextArea 的自定义类(覆盖了 scrollRectToVisible 方法)之间切换。

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.Rectangle;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionAdapter;

import javax.swing.Box;
import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JSplitPane;
import javax.swing.JTextArea;
import javax.swing.ScrollPaneConstants;
import javax.swing.SwingUtilities;

public class Main {
  static class MyTextArea extends JTextArea {
    @Override
    public void scrollRectToVisible(final Rectangle aRect) {
      // supress scrollToRect in textarea
    }
  }

  static final Box inner = Box.createVerticalBox();

  // if the jtextarea should contain text
  private static boolean textEnabled = true;
  private static boolean usejLabel = false;
  private static boolean useRebinding = false;
  private static boolean useLock = true;
  private static boolean customTextarea = false;

  private static boolean _locked = false;

  public static void main(final String[] args) {
    final JFrame frame = new JFrame();

    final JPanel insideScroll = insideScroll();
    final JScrollPane scrollpane = new JScrollPane(insideScroll);
    scrollpane.setAutoscrolls(false);
    scrollpane
        .setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);
    final JPanel rightPanel = new JPanel();
    rightPanel.setPreferredSize(new Dimension(300, 300));

    final MouseMotionAdapter listener = new MouseMotionAdapter() {

      @Override
      public void mouseDragged(final MouseEvent e) {
        super.mouseDragged(e);
        final boolean rebind = useRebinding;

        final MouseMotionAdapter self = this;
        if (rebind) {
          rightPanel.removeMouseMotionListener(self);
        }
        final int pos = scrollpane.getVerticalScrollBar().getValue();
        if (!useLock || !_locked) {
          if (useLock) {
            _locked = true;
          }
          update();
          SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
              if (rebind) {
                rightPanel.addMouseMotionListener(self);
              }
              if (useLock) {
                _locked = false;
              }
            }
          });
        }

      }
    };
    rightPanel.addMouseMotionListener(listener);

    // Add labels describing the problem
    rightPanel.setLayout(new BoxLayout(rightPanel, BoxLayout.PAGE_AXIS));
    final JButton toggleButton = new JButton("Toggle text");
    final JButton toggleButtonLabel = new JButton("Toggle JLable/JTextArea");
    final JButton toggleButtonRebind = new JButton("Turn rebinding on");
    final JButton toggleButtonCustomTextArea = new JButton(
        "Toggle Custom Textarea");
    rightPanel.add(toggleButton);
    rightPanel.add(toggleButtonLabel);
    rightPanel.add(toggleButtonRebind);
    rightPanel.add(toggleButtonCustomTextArea);
    rightPanel
        .add(new JLabel(
            "<html>If the text is disabled, you can press/drag<br> your mouse on on right side of the<br> window and the scrollbar will<br> stay in its position."));

    rightPanel
        .add(new JLabel(
            "<html><br/>If the text is enabled, the scrollbar<br> will jump around when dragging<br> on the right side."));

    rightPanel
        .add(new JLabel(
            "<html><br/>The problem does not occur when using JLabels instead of JTextArea"));

    // enable/disable the text when the button is clicked.
    toggleButton.addActionListener(new ActionListener() {
      @Override
      public void actionPerformed(final ActionEvent e) {
        textEnabled = !textEnabled;
        update();
      }
    });

    toggleButtonLabel.addActionListener(new ActionListener() {
      @Override
      public void actionPerformed(final ActionEvent e) {
        usejLabel = !usejLabel;
        update();
      }
    });
    toggleButtonRebind.addActionListener(new ActionListener() {
      @Override
      public void actionPerformed(final ActionEvent e) {
        useRebinding = !useRebinding;
        toggleButtonRebind.setText(useRebinding ? "Turn rebinding off"
            : "Turn rebinding on");
        update();
      }
    });
    toggleButtonCustomTextArea.addActionListener(new ActionListener() {
      @Override
      public void actionPerformed(final ActionEvent e) {
        customTextarea = !customTextarea;
        update();
      }
    });

    final JSplitPane split = new JSplitPane(JSplitPane.HORIZONTAL_SPLIT,
        scrollpane, rightPanel);

    frame.add(split);

    // initialize the scrollpane content
    update();

    frame.pack();
    frame.setVisible(true);

    frame.setLocationRelativeTo(null);

  }

  // initializes the components inside the scrollpane
  private static JPanel insideScroll() {
    final JPanel panel = new JPanel();
    panel.setLayout(new BorderLayout());
    panel.add(inner, BorderLayout.NORTH);

    return panel;
  }

  // replaces all components inside the scrollpane
  private static void update() {
    inner.removeAll();

    for (int i = 0; i < 30; i++) {
      inner.add(buildRow(i));
    }

    inner.revalidate();
  }

  // build a single component to be inserted into the scrollpane
  private static JPanel buildRow(final int i) {
    final JPanel row = new JPanel();

    final Color bg = i % 2 == 0 ? Color.DARK_GRAY : Color.LIGHT_GRAY;

    row.setBackground(bg);
    row.setPreferredSize(new Dimension(300, 80));
    row.setLayout(new BorderLayout());

    row.add(textarea(bg), BorderLayout.CENTER);

    return row;
  }

  // build the textarea to be inserted into the cells in the scroll pane
  private static Component textarea(final Color bg) {
    final String text = String.format("%d", (int) (1000 * Math.random()))
        + " Lorem ipsum dolor si amet. Lorem ipsum dolor si amet. Lorem ipsum dolor si amet";
    if (usejLabel) {
      final JLabel textarea = new JLabel();

      textarea.setBackground(bg);
      if (textEnabled) {
        textarea.setText(text);
      }

      return textarea;
    } else {
      final JTextArea textarea;
      if (customTextarea) {
        textarea = new MyTextArea();
        textarea.setDisabledTextColor(Color.cyan);

      } else {
        textarea = new JTextArea();
        textarea.setDisabledTextColor(Color.black);

      }

      textarea.setEnabled(false);
      textarea.setLineWrap(true);
      textarea.setBackground(bg);
      textarea.setEditable(false);
      if (textEnabled) {
        textarea.setText(text);
      }

      return textarea;
    }

  }
}

通过这样做，我意识到只有当 jscroll 包含将其文本设置为字符串的 jTextarea 元素时才会出现问题。在我的实际应用程序中，我需要自动换行的文本区域，但即使禁用换行也会出现问题。

Answer 1

我找到了解决方案。整个问题不在于 JScrollPane 本身，而在于如果文本不适合，则 JTextArea 调用自身的scrollRectToVisible。此调用通过 View 层次结构传播到 JScrollPane，导致它滚动到文本区域。

在我的例子中，我有 30 多个 JTextarea 且文本不断变化，这种情况经常发生。

我的解决方案是创建一个继承自 JTextArea 的自定义类，并使用空实现重写 scrollRectToVisible 方法。

这是工作示例:

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.Rectangle;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionAdapter;

import javax.swing.Box;
import javax.swing.BoxLayout;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JSplitPane;
import javax.swing.JTextArea;
import javax.swing.ScrollPaneConstants;

public class Main {
  // custom Textarea class
  static class MyTextArea extends JTextArea {
    @Override
    public void scrollRectToVisible(final Rectangle aRect) {
      // supress scrollToRect in textarea
    }
  }

  static final Box inner = Box.createVerticalBox();

  public static void main(final String[] args) {
    final JFrame frame = new JFrame();

    final JPanel insideScroll = insideScroll();
    final JScrollPane scrollpane = new JScrollPane(insideScroll);
    scrollpane.setAutoscrolls(false);
    scrollpane
    .setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);
    final JPanel rightPanel = new JPanel();
    rightPanel.setPreferredSize(new Dimension(300, 300));

    final MouseMotionAdapter listener = new MouseMotionAdapter() {

      @Override
      public void mouseDragged(final MouseEvent e) {
        super.mouseDragged(e);

        update();
      }
    };
    rightPanel.addMouseMotionListener(listener);

    // Add labels describing the problem
    rightPanel.setLayout(new BoxLayout(rightPanel, BoxLayout.PAGE_AXIS));

    final JSplitPane split = new JSplitPane(JSplitPane.HORIZONTAL_SPLIT,
        scrollpane, rightPanel);

    frame.add(split);

    // initialize the scrollpane content
    update();

    frame.pack();
    frame.setVisible(true);

    frame.setLocationRelativeTo(null);

  }

  // initializes the components inside the scrollpane
  private static JPanel insideScroll() {
    final JPanel panel = new JPanel();
    panel.setLayout(new BorderLayout());
    panel.add(inner, BorderLayout.NORTH);

    return panel;
  }

  // replaces all components inside the scrollpane
  private static void update() {
    inner.removeAll();

    for (int i = 0; i < 30; i++) {
      inner.add(buildRow(i));
    }

    inner.revalidate();
  }

  // build a single component to be inserted into the scrollpane
  private static JPanel buildRow(final int i) {
    final JPanel row = new JPanel();

    final Color bg = i % 2 == 0 ? Color.DARK_GRAY : Color.LIGHT_GRAY;

    row.setBackground(bg);
    row.setPreferredSize(new Dimension(300, 80));
    row.setLayout(new BorderLayout());

    row.add(textarea(bg), BorderLayout.CENTER);

    return row;
  }

  // build the textarea to be inserted into the cells in the scroll pane
  private static Component textarea(final Color bg) {
    final String text = String.format("%d", (int) (1000 * Math.random()))
        + " Lorem ipsum dolor si amet. Lorem ipsum dolor si amet. Lorem ipsum dolor si amet";

    final JTextArea textarea = new MyTextArea();
    textarea.setDisabledTextColor(Color.cyan);

    textarea.setEnabled(false);
    textarea.setLineWrap(true);
    textarea.setBackground(bg);
    textarea.setEditable(false);
    textarea.setText(text);

    return textarea;
  }

}

更新:我刚刚遇到了另一个线程，它提供了一个更好的解决方案来禁用 JTextArea 的自动滚动 - 无需子类化:

Java / Swing : JTextArea in a JScrollPane, how to prevent auto-scroll?