So you seem to be saying that the listeners installed by the UI
component itself
can process events directly on the EDT thread, but application code must
use invokeLater ?
This is particularly important for events which cause structural updates
to the model and the UI.
May I then suggest the following version of text on the package description:
--
Although it is generally safe to make updates to the UI immediately,
when executing on the event dispatch thread, there is an exception :
if a model listener tries to further change the UI before the UI has
been updated to
reflect a pending change then the UI may render incorrectly.
This can happen if an application installed listener needs to update the
UI in response
to an event which will cause a change in the model structure. It is
important to first allow
component installed listeners to process this change, since there is no
guarantee of the order
in which listeners may be called.
The solution is for the application listener to make the change using
{@link SwingUtilities.invokeLater}
so that any changes to UI rendering will be done post processing all the
model listeners
installed by the component.
---
-phil.
On 11/17/2017 06:11 PM, Krishna Addepalli wrote:
Hi Phil,
I have attached the code for your reference. However, the problem is
specifically in this function:
@Override
public void treeNodesInserted(final TreeModelEvent event) {
SwingUtilities./invokeLater/(() -> {
final TreePath pathToLastInsertedChild =
event.getTreePath().pathByAddingChild(event.getChildren()[event.getChildren().length
- 1]);
tree.setSelectionPath(pathToLastInsertedChild);
});
// final TreePath pathToLastInsertedChild =
//
event.getTreePath().pathByAddingChild(event.getChildren()[event.getChildren().length
- 1]);
// tree.setSelectionPath(pathToLastInsertedChild);
}
This is part of the TreeModelListener class, which receives callbacks
for any changes to the underlying model of the tree – like insertion,
deletion, structural changes etc. Now, the catch is even JTree has its
own ModelListener which listens to changes so that it can adapt its GUI.
In this case, the listeners seem to be called from last to first –
meaning the application registered listener will be called first and
then the components own ModelListener.
In the above function, the application (commented out code) tries to
highlight the path to the newly inserted node, which JTree has not yet
seen since its listener is not called yet. This leads to inconsistent
UI rendering, since it would be trying to show some node which is not
present.
For such cases, it is recommended to use “SwingUtilities.invokeLater”,
so that, the new UI event will be processed after JTree has had a
chance to update itself to the changes in the model.
Here is the code that is calling the listeners (in DefaultTreeModel.java):
protected void fireTreeNodesInserted(Object source, Object[] path,
int[] childIndices, Object[]
children) { // Guaranteed to return a non-null array Object[]
listeners = listenerList.getListenerList(); TreeModelEvent e = null;
// Process the listeners last to first, notifying // those that
are interested in this event for (int i = listeners.length-2; i>=0;
i-=2) { if (listeners[i]==TreeModelListener.class) { // Lazily create
the event: if (e == null) e = new
TreeModelEvent(source, path, childIndices, children);
((TreeModelListener)listeners[i+1]).treeNodesInserted(e); } } }
Thanks,
Krishna
*From:*Phil Race
*Sent:* Saturday, November 18, 2017 3:29 AM
*To:* Krishna Addepalli <[email protected]>;
[email protected]
*Subject:* Re: <Swing Dev> [10][JDK-8187936] Automatically selecting a
new JTree node in a model listener can cause unusual behavior.
Hi,
Whilst I could perhaps provide some very minor tweaks to the wording you
are adding, I would first like to understand the details of why the
rendering
becomes broken here since there doesn't seem to be anything intrinsically
wrong - only the model is being updated.
I've found that commenting out one of the other listener methods
BasicTreeUI.Handler.treeNodesInserted - "cures" it.
So what we seem to be saying here, is that when you get notification
of a change in the model, you must not make further changes in the model
until any UI listener has processed the first change .. and throwing this
on the queue via invokeLater is the obvious way to do that.
But I've run out of time to look at quite where the rendering breaks
and I'm not sure if this is as general a problem as the new comment
would imply.
So can you say something about why we miss rendering some nodes
and quite why BasicTreeUI.Handler.treeNodesInserted is breaking it.
-phil.
On 11/12/2017 11:07 PM, Krishna Addepalli wrote:
Hi Sergey,
Gentle reminder. Could you review?
Thanks,
Krishna
*From:* Krishna Addepalli
*Sent:* Wednesday, November 8, 2017 8:22 PM
*To:* [email protected] <mailto:[email protected]>
*Subject:* RE: [10][JDK-8187936] Automatically selecting a new
JTree node in a model listener can cause unusual behavior.
Hi Sergey,
Could you review this and let me know your feedback?
Thanks,
Krishna
*From:* Krishna Addepalli
*Sent:* Friday, October 27, 2017 4:43 PM
*To:* [email protected] <mailto:[email protected]>
*Subject:* [10][JDK-8187936] Automatically selecting a new JTree
node in a model listener can cause unusual behavior.
Hi All,
Please review the help text that is updated for this bug:
Bug: JDK-8187936: https://bugs.openjdk.java.net/browse/JDK-8187936
Webrev: http://cr.openjdk.java.net/~kaddepalli/8187936/webrev00/
<http://cr.openjdk.java.net/%7Ekaddepalli/8187936/webrev00/>
Summary:
As the bug title mentions, this is an unrecommended way of using
the model listeners. The code posted in the bug tries to update
the JTree path in the model listener callback, and since the JTree
is yet to change itself to the underlying model, it results in
weird UI behavior.
Attached code in the bug is corrected and re-uploaded.
This typically happens since listeners are called in a particular
order (either last to first or first to last in the order of
registration), and if the model listener tries to change the GUI
before the GUI has had a chance to react itself to the changes in
the underlying model. For example, highlighting a selection path
for a node added in the JTree, in the TreeModelListener callback
could lead to an extra node being added or existing nodes not
being shown, since JTree would not have yet updated its state
based on the model changes.
In such cases it is recommended to wrap the callback function
contents into a lambda, and invoke it through
“SwingUtilities.invokeLater”. This ensures that all the UI
elements have had a chance to react to the model changes, and any
UI actions will be guaranteed to operate on the updated widgets.
Similar update has been done in package-info.java for Swing, so
that it acts as a reference.
Thanks,
Krishna
