Java Tutorial/Swing Event/TreeWillExpandListener

TreeExpansionListener, TreeWillExpandListener

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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();
      }
    });
  }
}

Tree Will Expand Listener

public interface TreeWillExpandListener implements EventListener {
  public void treeWillCollapse(TreeExpansionEvent treeExpansionEvent)  throws ExpandVetoException;
  public void treeWillExpand(TreeExpansionEvent treeExpansionEvent)    throws ExpandVetoException;
}