I have a series of threads retrieving RSS feeds at regular intervals and want to refresh a custom JTree 开发者_StackOverflow社区using PropertyChangeSupport. However it uses a custom class implementing TreeModel and I'm not sure how to trigger an automatic change. Is this possible or should I use another class?
You'll have to use a collection of listeners of your model, and when your refreshing thread remarks some changes, you'll have to fire events to them. I don't think PropertyChangeSupport
will help you here much, as the Tree model's data is not in the form of Java beans properties, and you don't want to fire PropertyChangeEvents.
In a TreeModel implementation I did lastly, I made these methods (with german comments :-p)
/**
* Benachrichtigt die Listener, dass die Struktur unterhalb
* eines bestimmten Knotens komplett geändert wurde.
*/
private void fireStructureChanged(TreePath path) {
TreeModelEvent event = new TreeModelEvent(this, path);
for(TreeModelListener lis : listeners) {
lis.treeStructureChanged(event);
}
}
/**
* Benachrichtigt die Listener, dass unterhalb eines Knotens
* einige Knoten entfernt wurden.
*/
private void fireNodesRemoved(TreePath parentPath,
int[] indices, Object[] nodes) {
TreeModelEvent event =
new TreeModelEvent(this, parentPath, indices, nodes);
for(TreeModelListener lis : listeners) {
lis.treeNodesRemoved(event);
}
}
/**
* Benachrichtigt die Listener, dass ein bestimmter Knoten
* entfernt wurde.
*/
private void fireNodeRemoved(TreePath path, int index, Object node) {
fireNodesRemoved(path, new int[]{index}, new Object[]{node});
}
/**
* Benachrichtigt die Listener, dass sich das Aussehen einiger
* Unterknoten eines Knotens geändert hat.
*/
private void fireNodesChanged(TreePath parentPath,
int[] indices, Object[] nodes) {
TreeModelEvent event =
new TreeModelEvent(this, parentPath, indices, nodes);
for(TreeModelListener lis : listeners) {
lis.treeNodesChanged(event);
}
}
/**
* Benachrichtigt die Listener, dass sich das Aussehen eines Knotens
* geändert hat.
*
* @param parentPath der Pfad des Elternknotens des relevanten Knotens.
* @param index der Index des Knotens unterhalb des Elternknotens.
* Falls < 0, werden die Listener nicht benachrichtigt.
* @param node der Subknoten.
*/
private void fireNodeChanged(TreePath parentPath,
int index, Object node) {
if(index >= 0) {
fireNodesChanged(parentPath, new int[]{index}, new Object[]{node});
}
}
/**
* Benachrichtigt die Listener, dass unterhalb eines Knotens einige
* Knoten eingefügt wurden.
*/
private void fireNodesInserted(TreePath parentPath,
int[] indices, Object[] subNodes) {
TreeModelEvent event =
new TreeModelEvent(this, parentPath, indices, subNodes);
for(TreeModelListener lis : listeners) {
lis.treeNodesInserted(event);
}
}
/**
* Benachrichtigt die Listener, dass ein Knoten eingefügt wurde.
*/
private void fireNodeInserted(TreePath parentPath,
int index, Object node) {
fireNodesInserted(parentPath, new int[]{index}, new Object[]{node});
}
Then from the other parts of the model the right methods were invoked whenever something changed.
If you want to make it simple, you could simple always fire a treeStructureChanged
event with the root node, which would cause the whole tree to reload. For finer events, you'll need to look what in fact changed, and fire this.
Not entirely sure, what you mean by "refresh a tree by using a PropertyChangeListener", but agree with Paul: a PropertyChangeListener is not helpful in notifying the treeModel listeners (which include the JTree).
It is an intrinsic responsibility of any implementation of a TreeModel to notify its listeners by means of appropriate TreeModelEvents. If it listens to changes of contained nodes (which might fire f.i. PropertyChangeEvents) then it must translate those to TreeModelEvents.
A pseudo-code snippet:
public class MyTreeModel implements TreeModel {
PropertyChangeListener nodeListener;
// custom method to insert a node
public void addNodeTo(MyBean child, MyBean parent) {
// ... internal logic to add the new node
fireChildAdded(getPathToRoot(parent), child)
// add a PropertyChangeListener to new node so the model
// can comply to its notification contract
child.addPropertyChangeListener(getPropertyChangeListener();
}
protected void nodePropertyChanged(MyBean bean) {
firePathChanged(getPathToRoot(bean));
}
protected TreePath getPathToRoot(MyBean bean) {
// construct and return a treePath to the root
}
protected PropertyChangeListener getPropertyChangeListener() {
if (nodeListener == null) {
nodeListener = new PropertyChangeChangeListener() {
public void propertyChanged(...) {
nodeChanged((MyBean) e.getSource();
}
);
}
}
Constructing the actual events be a bit confusing (and is poorly documented), that's why SwingX has a helper class TreeModelSupport to simplify that task.
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