展开折叠展开与JTree延迟加载有关的问题

正如MadProgrammer解释的那样，这是一个小型演示示例，其中显示了一个JTree，它在树在节点上扩展时动态加载数据（并带有漂亮的加载栏作为奖励）：

import java.awt.BorderLayout;import java.awt.Dimension;import java.beans.PropertyChangeEvent;import java.beans.PropertyChangeListener;import java.beans.Transient;import java.util.ArrayList;import java.util.List;import javax.swing.Jframe;import javax.swing.JProgressBar;import javax.swing.JScrollPane;import javax.swing.JTree;import javax.swing.SwingUtilities;import javax.swing.SwingWorker;import javax.swing.UIManager;import javax.swing.UnsupportedLookAndFeelException;import javax.swing.event.TreeExpansionEvent;import javax.swing.event.TreeWillExpandListener;import javax.swing.tree.DefaultMutableTreeNode;import javax.swing.tree.DefaultTreeModel;import javax.swing.tree.ExpandVetoException;import javax.swing.tree.MutableTreeNode;import javax.swing.tree.TreePath;public class TestJTree {    public static class MyTreeNode extends DefaultMutableTreeNode {        private boolean loaded = false;        private int depth;        private final int index;        public MyTreeNode(int index, int depth) { this.index = index; this.depth = depth; add(new DefaultMutableTreeNode("Loading...", false)); setAllowsChildren(true); setUserObject("Child " + index + " at level " + depth);        }        private void setChildren(List<MyTreeNode> children) { removeAllChildren(); setAllowsChildren(children.size() > 0); for (MutableTreeNode node : children) {     add(node); } loaded = true;        }        @Override        public boolean isLeaf() { return false;        }        public void loadChildren(final DefaultTreeModel model, final PropertyChangeListener progressListener) { if (loaded) {     return; } SwingWorker<List<MyTreeNode>, Void> worker = new SwingWorker<List<MyTreeNode>, Void>() {     @Override     protected List<MyTreeNode> doInBackground() throws Exception {         // Here access database if needed         setProgress(0);         List<MyTreeNode> children = new ArrayList<TestJTree.MyTreeNode>();         if (depth < 5) {  for (int i = 0; i < 5; i++) {      // Simulate DB access time      Thread.sleep(300);      children.add(new MyTreeNode(i + 1, depth + 1));      setProgress((i + 1) * 20);  }         } else {  Thread.sleep(1000);         }         setProgress(0);         return children;     }     @Override     protected void done() {         try {  setChildren(get());  model.nodeStructureChanged(MyTreeNode.this);         } catch (Exception e) {  e.printStackTrace();  // Notify user of error.         }         super.done();     } }; if (progressListener != null) {     worker.getPropertyChangeSupport().addPropertyChangeListener("progress", progressListener); } worker.execute();        }    }    protected void initUI() {        Jframe frame = new Jframe(TestJTree.class.getSimpleName());        frame.setDefaultCloseOperation(Jframe.EXIT_ON_CLOSE);        MyTreeNode root = new MyTreeNode(1, 0);        final DefaultTreeModel model = new DefaultTreeModel(root);        final JProgressBar bar = new JProgressBar();        final PropertyChangeListener progressListener = new PropertyChangeListener() { @Override public void propertyChange(PropertyChangeEvent evt) {     bar.setValue((Integer) evt.getNewValue()); }        };        JTree tree = new JTree() { @Override @Transient public Dimension getPreferredSize() {     Dimension preferredSize = super.getPreferredSize();     preferredSize.width = Math.max(400, preferredSize.width);     preferredSize.height = Math.max(400, preferredSize.height);     return preferredSize; }        };        tree.setShowsRootHandles(true);        tree.addTreeWillExpandListener(new TreeWillExpandListener() { @Override public void treeWillExpand(TreeExpansionEvent event) throws ExpandVetoException {     TreePath path = event.getPath();     if (path.getLastPathComponent() instanceof MyTreeNode) {         MyTreeNode node = (MyTreeNode) path.getLastPathComponent();         node.loadChildren(model, progressListener);     } } @Override public void treeWillCollapse(TreeExpansionEvent event) throws ExpandVetoException { }        });        tree.setModel(model);        root.loadChildren(model, progressListener);        frame.add(new JScrollPane(tree));        frame.add(bar, BorderLayout.SOUTH);        frame.pack();        frame.setVisible(true);    }    public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException, UnsupportedLookAndFeelException {        UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());        SwingUtilities.invokeLater(new Runnable() { @Override public void run() {     new TestJTree().initUI(); }        });    }}