expandevent.html
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<TITLE>Listening for Expansion and Collapse Events in a JTree Component
(Java Developers Almanac Example)
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<META CONTENT="Patrick Chan" NAME="AUTHOR">
<META CONTENT="Code Examples from The Java Developers Almanac 1.4" NAME="DESCRIPTION">
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<B><A HREF="../javax.swing.tree/pkg.html#Events">Events</A></B><font color="#666666" SIZE="-2">
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<h3>
e1031.
Listening for Expansion and Collapse Events in a JTree Component</h3>
The tree component allows you to get events before and after a node
has been expanded or collapsed. The events that are fired before a
node is expanded or collapsed can be vetoed, thereby preventing the
operation.
<pre>
// Create tree
JTree tree = new JTree();
// Add pre-expansion event listener
tree.addTreeWillExpandListener(new MyTreeWillExpandListener());
// Add post-expansion event listener
tree.addTreeExpansionListener(new MyTreeExpansionListener());
// Pre-expansion/collapse event listener
public class MyTreeWillExpandListener implements TreeWillExpandListener {
public void treeWillExpand(TreeExpansionEvent evt) throws ExpandVetoException {
JTree tree = (JTree)evt.getSource();
// Get the path that will be expanded
TreePath path = evt.getPath();
// Cancel the operation if desired
boolean veto = <font color="#0066ff"><i>false</i></font>;
if (veto) {
throw new ExpandVetoException(evt);
}
}
public void treeWillCollapse(TreeExpansionEvent evt) throws ExpandVetoException {
JTree tree = (JTree)evt.getSource();
// Get the path that will be collapsed
TreePath path = evt.getPath();
// Cancel the operation if desired
boolean veto = <font color="#0066ff"><i>false</i></font>;
if (veto) {
throw new ExpandVetoException(evt);
}
}
}
// Post-expansion/collapse event listener
public class MyTreeExpansionListener implements TreeExpansionListener {
public void treeExpanded(TreeExpansionEvent evt) {
JTree tree = (JTree)evt.getSource();
// Get the path that was expanded
TreePath path = evt.getPath();
}
public void treeCollapsed(TreeExpansionEvent evt) {
JTree tree = (JTree)evt.getSource();
// Get the path that was collapsed
TreePath path = evt.getPath();
}
}
</pre>
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Related Examples
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e1032. <a class="eglink" href="SelectTree.html?l=rel">
Listening for Selection Events in a JTree Component
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See also:
<a class="eglink" href="/egs/javax.swing.tree/pkg.html?l=rel#Layout">
Layout
</a>
<a class="eglink" href="/egs/javax.swing.tree/pkg.html?l=rel#Node%20Expansion">
Node Expansion
</a>
<a class="eglink" href="/egs/javax.swing.tree/pkg.html?l=rel#Nodes">
Nodes
</a>
<a class="eglink" href="/egs/javax.swing.tree/pkg.html?l=rel#Selections">
Selections
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