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/ 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 HYPERLINK "mailto:[email protected]";<[email protected]>; HYPERLINK "mailto:[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: HYPERLINK "mailto:[email protected]"[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: HYPERLINK "mailto:[email protected]"[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: HYPERLINK "http://cr.openjdk.java.net/%7Ekaddepalli/8187936/webrev00/"http://cr.openjdk.java.net/~kaddepalli/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
