当我的JScrollPane中有超过50个组件时，每次用户决定转到下一页时，JScrollPane中的前10个组件都会被清除。
此功能工作正常并且是可取的，但是当删除组件时，视口/滚动会发生变化。每次清除组件时，滚动窗格的视图都会跳回。
我想要的是将视口保持在完全相同的位置，同时从JScrollPane中删除第一个组件。
目前我有一个解决方法，但它并不优雅，虽然它找到了用户的最后位置，但它不稳定，并跳转看起来不正确的滚动窗格：
if (middlePanel.getComponents().length > 50)
{
Component currentScroll = scrollPane.getViewport().getView();
for (int counter = 0; counter < memeAnchors.size(); counter++)
{
middlePanel.remove(counter);
}
scrollPane.setViewportView(currentScroll);
scrollPane.getVerticalScrollBar().setValue(scrollPane.getVerticalScrollBar().getValue() - 800);
}
我想做什么甚至可能？
先谢谢大家，
答案 0 :(得分：1)
好的，我撒谎没有回应。
执行此操作的一种方法如下所述SSCCE。注意使用Scrollable。解释在评论中：
import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.LayoutManager;
import java.awt.Rectangle;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;
@SuppressWarnings("serial")
public class Sscce extends JPanel {
private static final int INITIAL_ROW_COUNT = 100;
public static final int INCREMENTAL_ADD_ROW_COUNT = 10;
private static final int MIN_VERT_PERCENT = 4;
private static final int TIMER_DELAY = 250;
private ViewportViewPanel viewportViewPanel = new ViewportViewPanel(
new GridLayout(0, 1));
private JScrollPane scrollPane = new JScrollPane(viewportViewPanel);
private BoundedRangeModel vertModel;
private Timer vertChangeTimer;
private int viewportViewPanelIndex = 0;
public Component firstViewedComp;
public Sscce() {
setLayout(new BorderLayout());
add(scrollPane);
for (viewportViewPanelIndex = 0; viewportViewPanelIndex < INITIAL_ROW_COUNT; viewportViewPanelIndex++) {
viewportViewPanel.add(new ViewablePanel(viewportViewPanelIndex));
}
vertModel = scrollPane.getVerticalScrollBar().getModel();
vertModel.addChangeListener(new VertModelChangeListener());
}
private class VertModelChangeListener implements ChangeListener {
@Override
public void stateChanged(ChangeEvent cEvt) {
// if timer is running, get out of here
if (vertChangeTimer != null && vertChangeTimer.isRunning()) {
return;
}
// if haven't set firstViewedComp back to null (done in Timer) get out of here
if (firstViewedComp != null) {
return;
}
// check to see if near bottom
int diff = vertModel.getMaximum() - vertModel.getValue()
- vertModel.getExtent();
int normalizedDiff = (100 * diff) / vertModel.getMaximum();
// if not near bottom, get out of here
if (normalizedDiff >= MIN_VERT_PERCENT) {
return;
}
// create and start timer
vertChangeTimer = new Timer(TIMER_DELAY, new VertChangeTimerListener());
vertChangeTimer.setRepeats(false);
vertChangeTimer.start();
// get viewport and its rectangle
JViewport viewport = scrollPane.getViewport();
Rectangle viewRect = viewport.getViewRect();
// find first component that is inside of viewport's rectangle
Component[] components = viewportViewPanel.getComponents();
for (Component component : components) {
if (viewRect.contains(component.getBounds())) {
if (firstViewedComp == null) {
firstViewedComp = component; // first component found
break;
}
}
}
// delete 10 components at start
// add 10 components add end
for (int i = 0; i < INCREMENTAL_ADD_ROW_COUNT; i++) {
viewportViewPanel.remove(components[i]);
viewportViewPanel.add(new ViewablePanel(viewportViewPanelIndex));
viewportViewPanelIndex++;
}
// redo laying out components and repainting the container
viewportViewPanel.revalidate();
viewportViewPanel.repaint();
// scroll back to first viewed component, but give a little delay to allow
// layout out above to complete. So queue it on the event queue via invokeLater
SwingUtilities.invokeLater(new Runnable() {
public void run() {
viewportViewPanel.scrollRectToVisible(firstViewedComp
.getBounds());
}
});
}
}
// the timer listener. it just nulls out the first viewed component
private class VertChangeTimerListener implements ActionListener {
@Override
public void actionPerformed(ActionEvent e) {
firstViewedComp = null;
}
}
private static void createAndShowGui() {
Sscce mainPanel = new Sscce();
JFrame frame = new JFrame("Sscce");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(mainPanel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}
// JPanel that is held by the JScrollPane's JViewport and that holds the smaller
// JPanels. Note that it implements Scrollable
@SuppressWarnings("serial")
class ViewportViewPanel extends JPanel implements Scrollable {
private static final int BLOCK = 8;
public ViewportViewPanel(LayoutManager layout) {
super(layout);
}
@Override
public Dimension getPreferredScrollableViewportSize() {
int scrollWidth = ViewablePanel.PREF_W;
int scrollHeight = ViewablePanel.PREF_H * BLOCK;
return new Dimension(scrollWidth, scrollHeight);
}
@Override
public int getScrollableBlockIncrement(Rectangle visibleRectangle,
int orientation, int direction) {
if (orientation == SwingConstants.VERTICAL) {
return ViewablePanel.PREF_H * (3 * BLOCK) / 4;
}
return 0;
}
@Override
public boolean getScrollableTracksViewportHeight() {
return false;
}
@Override
public boolean getScrollableTracksViewportWidth() {
return true;
}
@Override
public int getScrollableUnitIncrement(Rectangle visibleRect,
int orientation, int direction) {
if (orientation == SwingConstants.VERTICAL) {
return ViewablePanel.PREF_H;
}
return 1;
}
}
// small JPanel. Many of these are held in a single GridLayout column
// by the JPanel above.
@SuppressWarnings("serial")
class ViewablePanel extends JPanel {
public static final int PREF_W = 400;
public static final int PREF_H = 50;
private int index;
public ViewablePanel(int index) {
this.setIndex(index);
String title = "index " + index;
setBorder(BorderFactory.createTitledBorder(title));
}
@Override
public Dimension getPreferredSize() {
return new Dimension(PREF_W, PREF_H);
}
public int getIndex() {
return index;
}
public void setIndex(int index) {
this.index = index;
}
}