Java Tutorial/Swing Event/TreeWillExpandListener

TreeExpansionListener, TreeWillExpandListener

   <source lang="java">

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/*

* TreeExpandEventDemo2.java requires no other files.
*/

import java.awt.Dimension; import java.awt.GridBagConstraints; import java.awt.GridBagLayout; import java.awt.Insets; import javax.swing.BorderFactory; import javax.swing.JComponent; import javax.swing.JFrame; import javax.swing.JOptionPane; import javax.swing.JPanel; import javax.swing.JScrollPane; import javax.swing.JTextArea; import javax.swing.JTree; import javax.swing.event.TreeExpansionEvent; import javax.swing.event.TreeExpansionListener; import javax.swing.event.TreeWillExpandListener; import javax.swing.tree.DefaultMutableTreeNode; import javax.swing.tree.ExpandVetoException; import javax.swing.tree.TreeNode; public class TreeExpandEventDemo2 extends JPanel {

 DemoArea demoArea;
 JTextArea textArea;
 final static String newline = "\n";
 public TreeExpandEventDemo2() {
   super(new GridBagLayout());
   GridBagLayout gridbag = (GridBagLayout) getLayout();
   GridBagConstraints c = new GridBagConstraints();
   c.fill = GridBagConstraints.BOTH;
   c.gridwidth = GridBagConstraints.REMAINDER;
   c.weightx = 1.0;
   c.weighty = 1.0;
   c.insets = new Insets(1, 1, 1, 1);
   demoArea = new DemoArea();
   gridbag.setConstraints(demoArea, c);
   add(demoArea);
   c.insets = new Insets(0, 0, 0, 0);
   textArea = new JTextArea();
   textArea.setEditable(false);
   JScrollPane scrollPane = new JScrollPane(textArea);
   scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
   scrollPane.setPreferredSize(new Dimension(200, 75));
   gridbag.setConstraints(scrollPane, c);
   add(scrollPane);
   setPreferredSize(new Dimension(450, 450));
   setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));
 }
 void saySomething(String eventDescription, TreeExpansionEvent e) {
   textArea
       .append(eventDescription + "; " + "path = " + e.getPath() + newline);
 }
 class DemoArea extends JScrollPane implements TreeExpansionListener,
     TreeWillExpandListener {
   Dimension minSize = new Dimension(100, 100);
   JTree tree;
   Object[] willExpandOptions = { "Cancel Expansion", "Expand" };
   String willExpandText = "A branch node is about to be expanded.\n"
       + "Click \"Cancel Expansion\" to prevent it.";
   String willExpandTitle = "Tree Will Expand";
   public DemoArea() {
     TreeNode rootNode = createNodes();
     tree = new JTree(rootNode);
     tree.addTreeExpansionListener(this);
     tree.addTreeWillExpandListener(this);
     setViewportView(tree);
   }
   private TreeNode createNodes() {
     DefaultMutableTreeNode root;
     DefaultMutableTreeNode grandparent;
     DefaultMutableTreeNode parent;
     DefaultMutableTreeNode child;
     root = new DefaultMutableTreeNode("San Francisco");
     grandparent = new DefaultMutableTreeNode("Potrero Hill");
     root.add(grandparent);
     //
     parent = new DefaultMutableTreeNode("Restaurants");
     grandparent.add(parent);
     child = new DefaultMutableTreeNode("Thai Barbeque");
     parent.add(child);
     child = new DefaultMutableTreeNode("Goat Hill Pizza");
     parent.add(child);
     //
     parent = new DefaultMutableTreeNode("Grocery Stores");
     grandparent.add(parent);
     child = new DefaultMutableTreeNode("Good Life Grocery");
     parent.add(child);
     child = new DefaultMutableTreeNode("Safeway");
     parent.add(child);
     grandparent = new DefaultMutableTreeNode("Noe Valley");
     root.add(grandparent);
     //
     parent = new DefaultMutableTreeNode("Restaurants");
     grandparent.add(parent);
     child = new DefaultMutableTreeNode("Hamano Sushi");
     parent.add(child);
     child = new DefaultMutableTreeNode("Hahn"s Hibachi");
     parent.add(child);
     //
     parent = new DefaultMutableTreeNode("Grocery Stores");
     grandparent.add(parent);
     child = new DefaultMutableTreeNode("Real Foods");
     parent.add(child);
     child = new DefaultMutableTreeNode("Bell Market");
     parent.add(child);
     return root;
   }
   public Dimension getMinimumSize() {
     return minSize;
   }
   public Dimension getPreferredSize() {
     return minSize;
   }
   // Required by TreeWillExpandListener interface.
   public void treeWillExpand(TreeExpansionEvent e) throws ExpandVetoException {
     saySomething("Tree-will-expand event detected", e);
     int n = JOptionPane.showOptionDialog(this, willExpandText,
         willExpandTitle, JOptionPane.YES_NO_OPTION,
         JOptionPane.QUESTION_MESSAGE, null, willExpandOptions,
         willExpandOptions[1]);
     if (n == 0) {
       // User said cancel expansion.
       saySomething("Tree expansion cancelled", e);
       throw new ExpandVetoException(e);
     }
   }
   // Required by TreeWillExpandListener interface.
   public void treeWillCollapse(TreeExpansionEvent e) {
     saySomething("Tree-will-collapse event detected", e);
   }
   // Required by TreeExpansionListener interface.
   public void treeExpanded(TreeExpansionEvent e) {
     saySomething("Tree-expanded event detected", e);
   }
   // Required by TreeExpansionListener interface.
   public void treeCollapsed(TreeExpansionEvent e) {
     saySomething("Tree-collapsed event detected", e);
   }
 }
 /**
  * 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("TreeExpandEventDemo2");
   frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
   // Create and set up the content pane.
   JComponent newContentPane = new TreeExpandEventDemo2();
   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();
     }
   });
 }

}</source>

Tree Will Expand Listener

   <source lang="java">

public interface TreeWillExpandListener implements EventListener {

 public void treeWillCollapse(TreeExpansionEvent treeExpansionEvent)  throws ExpandVetoException;
 public void treeWillExpand(TreeExpansionEvent treeExpansionEvent)    throws ExpandVetoException;

}</source>