swing:滚动到jscrollpane的底部,条件是当前的视区位置

看看 scrollRectToVisible(Rectangle r) 和 modelToView(int pos)

这样你就能在不影响用户选择的情况下找到你想要的东西。

对于滚动条,尝试在不同的事件上强制执行滚动和附加到。例如:

if (atBottom) {
    // append new line & do scroll
    SwingUtilities.invokerLater(new Runnable(){
        public void run() {
            // append text
        }});
} else {
    // append newline
    // append text
}

基于前面的答案和进一步的google搜索,我做了一个测试,在这个测试中,一个线程连续地将字符串附加到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,jscrollbar需要用新的最大值进行更新。使用invokelater,awt线程将处理这个问题。

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;
    }
}

看看这个 example .

不过,我将更改代码以使用以下更有效的代码:

caret.setDot(textArea.getDocument().getLength());

过去几天我一直在尝试不同的方法来解决这个问题。我找到的最佳解决方案是替换jscrollpane的viewport的布局管理器,并在那里实现所有所需的滚动行为。跳跃的滚动条旋钮不见了,它燃烧的很快——如此之快,以至于它创造了另一个我不得不努力的比赛条件。详情如下: http://www.java-forums.org/awt-swing/56808-scroll-bar-knob-jumpy-when-component-growing.html

有点晚了,但我发现: http://www.camick.com/java/source/SmartScroller.java

实际上,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;
    }
}

public static void scrollToBottom(JComponent component) 
{
    Rectangle visibleRect = component.getVisibleRect();
    visibleRect.y = component.getHeight() - visibleRect.height;
    component.scrollRectToVisible(visibleRect);
}

你可以在这里找到全部细节: How to make JTextPane autoscroll only when scroll bar is at bottom and scroll lock is off?

DefaultCaret caret = (DefaultCaret)textArea.getCaret();  
caret.setUpdatePolicy(DefaultCaret.ALWAYS_UPDATE);