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Steps to reproduce 1) Open Java perspective 2) Detach outline view 3) Open Debug perspective 4) Detach outline view 5) Re-attach outline view Notice NPE. If you detach different views in the two perspectives the re-attach works fine. The problem only seems to happen when you detach the same view in each perspective. Here is the stack trace I see: !ENTRY org.eclipse.equinox.event 4 0 2011-09-30 08:51:08.026 !MESSAGE Exception while dispatching event org.osgi.service.event.Event [topic=org/eclipse/e4/ui/model/ui/ElementContainer/children/ADD] to handler org.eclipse.e4.ui.services.internal.events.UIEventHandler@5d7c5d7c !STACK 0 java.lang.NullPointerException at org.eclipse.e4.ui.internal.workbench.ModelServiceImpl.setStackVisibility(ModelServiceImpl.java:942) at org.eclipse.e4.ui.internal.workbench.ModelServiceImpl.setStackVisibility(ModelServiceImpl.java:951) at org.eclipse.e4.ui.internal.workbench.ModelServiceImpl.setStackVisibility(ModelServiceImpl.java:951) at org.eclipse.e4.ui.internal.workbench.ModelServiceImpl.hideLocalPlaceholders(ModelServiceImpl.java:931) at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$4.handleEvent(PartRenderingEngine.java:278) at org.eclipse.e4.ui.services.internal.events.UIEventHandler$1.run(UIEventHandler.java:41) at org.eclipse.swt.widgets.Synchronizer.syncExec(Synchronizer.java:180) at org.eclipse.ui.internal.UISynchronizer.syncExec(UISynchronizer.java:150) at org.eclipse.swt.widgets.Display.syncExec(Display.java:4683) at org.eclipse.e4.ui.internal.workbench.swt.E4Application$1.syncExec(E4Application.java:182) at org.eclipse.e4.ui.services.internal.events.UIEventHandler.handleEvent(UIEventHandler.java:38) at org.eclipse.equinox.internal.event.EventHandlerWrapper.handleEvent(EventHandlerWrapper.java:197) at org.eclipse.equinox.internal.event.EventHandlerTracker.dispatchEvent(EventHandlerTracker.java:197) at org.eclipse.equinox.internal.event.EventHandlerTracker.dispatchEvent(EventHandlerTracker.java:1) at org.eclipse.osgi.framework.eventmgr.EventManager.dispatchEvent(EventManager.java:230) at org.eclipse.osgi.framework.eventmgr.ListenerQueue.dispatchEventSynchronous(ListenerQueue.java:148) at org.eclipse.equinox.internal.event.EventAdminImpl.dispatchEvent(EventAdminImpl.java:135) at org.eclipse.equinox.internal.event.EventAdminImpl.sendEvent(EventAdminImpl.java:78) at org.eclipse.equinox.internal.event.EventComponent.sendEvent(EventComponent.java:39) at org.eclipse.e4.ui.services.internal.events.EventBroker.send(EventBroker.java:81) at org.eclipse.e4.ui.internal.workbench.UIEventPublisher.notifyChanged(UIEventPublisher.java:55) at org.eclipse.emf.common.notify.impl.BasicNotifierImpl.eNotify(BasicNotifierImpl.java:380) at org.eclipse.emf.ecore.util.EcoreEList.dispatchNotification(EcoreEList.java:255) at org.eclipse.emf.common.notify.impl.NotifyingListImpl.addUnique(NotifyingListImpl.java:362) at org.eclipse.emf.common.util.AbstractEList.add(AbstractEList.java:345) at org.eclipse.e4.ui.internal.workbench.ModelServiceImpl.combine(ModelServiceImpl.java:512) at org.eclipse.e4.ui.internal.workbench.ModelServiceImpl.insert(ModelServiceImpl.java:550) at org.eclipse.e4.ui.workbench.addons.dndaddon.SplitDropAgent.dock(SplitDropAgent.java:331) at org.eclipse.e4.ui.workbench.addons.dndaddon.SplitDropAgent.drop(SplitDropAgent.java:161) at org.eclipse.e4.ui.workbench.addons.dndaddon.DnDManager.finishDrag(DnDManager.java:222) at org.eclipse.e4.ui.workbench.addons.dndaddon.DnDManager.startDrag(DnDManager.java:200) at org.eclipse.e4.ui.workbench.addons.dndaddon.DnDManager$1$1.dragDetected(DnDManager.java:109) at org.eclipse.swt.widgets.TypedListener.handleEvent(TypedListener.java:127) at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84) at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1053) at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:4165) at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3754) at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$9.run(PartRenderingEngine.java:972) at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332) at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:888) at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:90) at org.eclipse.ui.internal.Workbench$3.run(Workbench.java:565) at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332) at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:520) at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:149) at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:123) at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196) at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:110) at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:79) at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:344) at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:179) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:79) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:618) at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:624) at org.eclipse.equinox.launcher.Main.basicRun(Main.java:579) at org.eclipse.equinox.launcher.Main.run(Main.java:1431) at org.eclipse.equinox.launcher.Main.main(Main.java:1407)
It looks like this might be some kind of parenting problem. Here are different steps that do not produce the NPE but cause the reattached view to be reattached in both perspectives ... which is bogus. If this problem has a different cause we should create a new defect, but I'm guessing the cause of the two behaviors is the same. 1) Open Java perspective 2) Detach outline view 3) Open Debug perspective 4) Detach outline view 5) Reattach outline view in Debug perspective 6) Switch to Java perspective Notice that the outline view is now showing up as attached in the Java perspective.
Actually detaching the view is not a requirement to see some bogus behaviour. Try this. 1) Open Java perspective 2) Open Debug perspective 3) Move the Outline view to somewhere new in the Debug perspective 4) Open the java perspective Notice the Outline view has moved. Also I can get even stranger behavoiur if I go back to the debug perspective and move the outline view again. I've even gotten the outline view to disappear from the Java perspective by manipulating it in the debug perspective. I'm not entirely sure this problem would have the same cause as the steps in comment 1 and 2. But new bugs can be created as needed I guess.
For comment #2, the problem only seems to happen if the drop area is the shared editor area.
Same is true for comment 1. The NPE only happens if you try to re-attach the the view in the shared MArea. Which makes sense. Is the solution simply that the MArea should not be a valid drop target for views?
(In reply to comment #4) > Is the solution simply that the MArea should not be a valid drop target for > views? This is one of the features we provide for Eclipse 4 so this would be a no-go.
I have confused this defect with some reports of problems that are designed behaviour. To clean things up I'm going to close it as invalid and open a new defect.
The new defect is https://bugs.eclipse.org/bugs/show_bug.cgi?id=359583
