Hi Phil
Thank you for your time in understanding the issue and rephrasing the
text. I have created a new webrev, with the text you mentioned, and
here it is: http://cr.openjdk.java.net/~kaddepalli/8187936/webrev01/
<http://cr.openjdk.java.net/%7Ekaddepalli/8187936/webrev01/>
Regards,
Krishna
*From:*Phil Race
*Sent:* Wednesday, December 6, 2017 10:17 PM
*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.
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]>
<mailto:[email protected]>; [email protected]
<mailto:[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
