问题
The SSCCE of the problem is as follows. I am dynamically populating JTree, but nothing is happening.
import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Vector;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTree;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.DefaultTreeModel;
import javax.swing.tree.TreePath;
public class DynamicTreeDemo extends JFrame
implements ActionListener {
private int newNodeSuffix = 1;
private static String ADD_COMMAND = "add";
private static String REMOVE_COMMAND = "remove";
private static String CLEAR_COMMAND = "clear";
private JTree jtrMainMenu;
DefaultMutableTreeNode rootNode = null;
DefaultTreeModel treeModel;
public DynamicTreeDemo() {
super(new BorderLayout());
//Create the components.
jtrMainMenu = new JTree();
populateTree();
JButton addButton = new JButton("Add");
addButton.setActionCommand(ADD_COMMAND);
addButton.addActionListener(this);
JButton removeButton = new JButton("Remove");
removeButton.setActionCommand(REMOVE_COMMAND);
removeButton.addActionListener(this);
JButton clearButton = new JButton("Clear");
clearButton.setActionCommand(CLEAR_COMMAND);
clearButton.addActionListener(this);
//Lay everything out.
jtrMainMenu.setPreferredSize(new Dimension(300, 150));
add(jtrMainMenu, BorderLayout.CENTER);
JPanel panel = new JPanel(new GridLayout(0,3));
panel.add(addButton);
panel.add(removeButton);
panel.add(clearButton);
add(panel, BorderLayout.SOUTH);
}
public void populateTree() {
Vector<Vector<String>> data =GetDataFromDB();
java.util.List<String> list =GetListFromDB();
int i=0;;
int size=list.size();
treeModel=(DefaultTreeModel)jtrMainMenu.getModel();
((DefaultMutableTreeNode) (treeModel.getRoot())).removeAllChildren();
treeModel.reload();
rootNode = new DefaultMutableTreeNode("JewelleryERPApplication");
treeModel=new DefaultTreeModel(rootNode);
DefaultMutableTreeNode p1=null, p2=null,p3=null,p4=null,p5=null;
while(i<size){
if(list.get(i).length()==2){
p1 = addObject(null, data.get(i).elementAt(1),true);
}else
if(list.get(i).length()==4){
p2 = addObject(p1, data.get(i).elementAt(1),true);
}else if
(list.get(i).length()==6){
p3 = addObject(p2, data.get(i).elementAt(1),true);
}
else if
(list.get(i).length()==8){
p4 = addObject(p3, data.get(i).elementAt(1),true);
}
else if
(list.get(i).length()==10){
p5 = addObject(p4, data.get(i).elementAt(1),true);
}
i++;
}
jtrMainMenu.setModel(treeModel);
((DefaultMutableTreeNode) (treeModel.getRoot())).getChildCount();
jtrMainMenu.revalidate();
jtrMainMenu.repaint();
}
public DefaultMutableTreeNode addObject(DefaultMutableTreeNode parent,
Object child,
boolean shouldBeVisible) {
DefaultMutableTreeNode childNode =
new DefaultMutableTreeNode(child);
if (parent == null) {
parent = rootNode;
}
//It is key to invoke this on the TreeModel, and NOT DefaultMutableTreeNode
treeModel.insertNodeInto(childNode, parent,
parent.getChildCount());
jtrMainMenu.setModel(treeModel);
//Make sure the user can see the lovely new node.
if (shouldBeVisible) {
jtrMainMenu.scrollPathToVisible(new TreePath(childNode.getPath()));
}
return childNode;
}
/**
* Create the GUI and show it. For thread safety,
* this method should be invoked from the
* event-dispatching thread.
*/
private static void createAndShowGUI() {
//Create and set up the window.
JFrame frame = new JFrame("DynamicTreeDemo");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//Create and set up the content pane.
DynamicTreeDemo newContentPane = new DynamicTreeDemo();
newContentPane.setOpaque(true); //content panes must be opaque
frame.setContentPane(newContentPane);
//Display the window.
frame.pack();
frame.setVisible(true);
}
public static void main(String[] args) {
//Schedule a job for the event-dispatching thread:
//creating and showing this application's GUI.
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGUI();
}
});
}
}
回答1:
There are a number of problems with you code, but...the major problem (I think) you're having is the fact that when you reload the model, the root node is collapsed by default.
If the root node is hidden and/or it's handle is hidden, it will appear as if nothing has been loaded.
Unhide these elements for testing.
You can also expand the root node once the model has been reloaded...
!! Warning !! Don't run this on your root directory !! It will scan all child directories and that could take more time then you're actually willing to wait for :P
import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.File;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTree;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.DefaultTreeModel;
import javax.swing.tree.TreePath;
public class FileTree {
public static void main(String[] args) {
new FileTree();
}
public FileTree() {
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
}
JFrame frame = new JFrame("Testing");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(new BorderLayout());
frame.add(new TestPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class TestPane extends JPanel {
private DefaultTreeModel model;
private JTree tree;
public TestPane() {
setLayout(new BorderLayout());
tree = new JTree();
File rootFile = new File(".");
DefaultMutableTreeNode root = new DefaultMutableTreeNode(rootFile);
model = new DefaultTreeModel(root);
tree.setModel(model);
tree.setRootVisible(true);
tree.setShowsRootHandles(true);
add(new JScrollPane(tree));
JButton load = new JButton("Load");
add(load, BorderLayout.SOUTH);
load.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
DefaultMutableTreeNode root = (DefaultMutableTreeNode) model.getRoot();
root.removeAllChildren();
model.reload();
File rootFile = (File) root.getUserObject();
addFiles(rootFile, model, root);
tree.expandPath(new TreePath(root));
}
});
}
@Override
public Dimension getPreferredSize() {
return new Dimension(200, 200);
}
protected void addFiles(File rootFile, DefaultTreeModel model, DefaultMutableTreeNode root) {
for (File file : rootFile.listFiles()) {
DefaultMutableTreeNode child = new DefaultMutableTreeNode(file);
model.insertNodeInto(child, root, root.getChildCount());
if (file.isDirectory()) {
addFiles(file, model, child);
}
}
}
}
}
Code Review
You should avoid extending directly from JFrame. From the looks of you example, you weren't, but hacked it in, but it's inadvisable anyway...
This...
jtrMainMenu.setPreferredSize(new Dimension(300, 150));
add(jtrMainMenu, BorderLayout.CENTER);
This is inadvisable. JTree should be added to JScrollPane.
This...
private static void createAndShowGUI() {
//Create and set up the window.
JFrame frame = new JFrame("DynamicTreeDemo");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//Create and set up the content pane.
BadTree newContentPane = new BadTree();
newContentPane.setOpaque(true); //content panes must be opaque
frame.setContentPane(newContentPane);
//Display the window.
frame.pack();
frame.setVisible(true);
}
Isn't going to work either (based on your example), as anything that extends from Window can not be added to any other container that extends Window
Unless your base component is extending from JComponent, must other components are opaque (JLabel is an obvious exception), so setting the newContentPane to opaque may be a mute point.
来源：https://stackoverflow.com/questions/15215578/how-to-build-a-jtree-dynamically