<Swing Dev> Patch for NPE at javax.swing.plaf.basic.BasicTreeUI$Actions.page:4470

[Alexander Scherbatiy]

On 11/15/2012 7:58 PM, Jaroslav Tulach wrote:
> Dear Swing maintainers,
> my name is Jaroslav Tulach and I am maintaining NetBeans explorer - a
> component that is using JTree heavily.
>
> > From time to time I receive a user report with a NPE from Swing where little
> or even no NetBeans code involved. Just today I got
> http://netbeans.org/bugzilla/show_bug.cgi?id=222081
> We have about 35 other ones (which is not that much given the fact we have
> million of users), but still...
>
> According to
> http://statistics.netbeans.org/exceptions/exception.do?id=628832
> the report comes from jdk7u9-b05. The source code is here
> http://hg.openjdk.java.net/jdk7u/jdk7u/jdk/file/jdk7u9-
> b05/src/share/classes/javax/swing/plaf/basic/BasicTreeUI.java
> and thus it looks like the call on line 4468 to
>
> ui.getPathBounds(tree, newPath);
>
> can return null (under some rare and unknown circumstances).
>
> I can close the bug #222081 as "worksforme", but it is clear that such error
> happens from time to time and we don't want our users to face errors. A
> simple:
>
> 4469 if (newRect == null) return;
>
> would do the trick. One question remains: if I try to donate such patch, will
> you accept it?
     The ui.getPathBounds(tree, newPath) method definitely can return 
null so it needs to have this check.
     However, such fix can mask the real issue, for example, in the 
treeState.getBounds() method where the  treeState can be instance of 
FixedHeightLayoutCache or VariableHeightLayoutCache class.

     If it is possible, could you send a code snippet that shows how 
NetBeans uses JTree? May be it can give a hint what can be wrong in this 
case.

     Thanks,
     Alexandr.


> -jt
>
>