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https://issues.apache.org/jira/browse/NETBEANS-4754?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17187979#comment-17187979
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Svatopluk Dedic commented on NETBEANS-4754:
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{quote}> it's a job of the ctx aware instance to monitor the data changes
Which instance are you referring to here? Which class?
{quote}
If a {{ContextAwareInstance}}.createInstance() is called with some Lookup, the
result object's job is to adapt to possible changes in that Lookup's contents –
if it looks for an item that CAN be changed, of course.
{quote} Is the delegate0 method expected to be called every time the context
changes, or only when the user invokes the action?
{quote}
IIRC, it is called by all {{isEnabled}}, {{isSelected}} (for on/off actions)
swing callbacks. Re. caching ... maybe it could be removed; and I'd opt for it,
if the (relatively) simple change outlined above is not sufficient.
{quote}when focus is shifted from the TopComponent that provides the context
object to, say, the "Files" sidebar tab. I'm not sure this would be fixed by
making changes in delegate0.
{quote}
Could be, since a different Lookup instance (the one from Files TC) will be
provided to delegate0 -> new instance should be created.
> Action gets called with wrong context until garbage collection
> --------------------------------------------------------------
>
> Key: NETBEANS-4754
> URL: https://issues.apache.org/jira/browse/NETBEANS-4754
> Project: NetBeans
> Issue Type: Bug
> Components: platform - Actions
> Affects Versions: 12.0
> Environment: NetBeans Platform application running on NetBeans
> Platform 12.0 on Windows 10 / Java 13.0.2.
> Reporter: Eirik Bakke
> Assignee: Svatopluk Dedic
> Priority: Major
>
> My NetBeans Platform application has an action declared as follows:
> {code:java}
> @ActionID(category = "Ultorg", id = "com.ultorg.actionids.FieldsAction")
> @ActionRegistration(displayName = "#CTL_FieldsAction")
> @Messages("CTL_FieldsAction=Fields & Joins...")
> public class FieldsAction implements ActionListener {
> private final ToolboxInvoker invoker;
> public FieldsAction(ToolboxInvoker invoker) {
> Preconditions.checkNotNull(invoker);
> this.invoker = invoker;
> }
> @Override
> public void actionPerformed(ActionEvent e) {
> invoker.invoke();
> }
> }
> {code}
> The ToolboxInvoker context is provided by the lookup of a custom TopComponent
> implementation. When I have multiple such TopComponent tabs open, switching
> between them, and invoking the action above with a keyboard shortcut, the
> wrong FieldsAction instance will occasionally be called (i.e. an instance
> with the wrong ToolboxInvoker context).
> After some debugging, the problem seems to be caused by
> https://github.com/apache/netbeans/pull/652 , specifically by
> ContextAction.delegate0 assuming that instDelegate can be used as a cached
> value without checking whether the lookup (data parameter) has changed. Or
> perhaps instDelegate was supposed to be cleared elsewhere whenever the lookup
> changes--but this is not happening properly.
> Because the instDelegate field holds only weak references, the buggy state
> only lasts until the next garbage collection.
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