JList - Nullpointer Exception

[Nizar1984]

Hallo,

Folgendes Szenario. In die JList "jlCast " mit dem DefaultListModel "dlm" wird der Array "coActorArray" übergeben:

  for(int i = 0; i<coActorArray.length; i++)
		    	dlmModel.addElement(coActorArray[i]);
		    jlCast = new JList(dlmModel);

Diese Liste enthält alle von einer Datenbank geholten Daten.

Über einen Action Listener werden Elemente aus der Liste aus der Datenbank entfernt, und die Liste macht automatisch ein Update, sodass bei jeder Lösch Operation die Liste auf den neusten Stand gebracht wird.

if(e.getActionCommand().equals("Remove Cast"))
{
			
    Actor coActor = (Actor) jlCast.getSelectedValue();

        if(coActor!=null)
            {
			
	         coActorManager.removeActorFromMovie(iMovieToEditID, coActor.getId());
			
	         try 
        	 {
		      coActorArray = coActorManager.getActorsByMovieID(iMovieToEditID);
	          } 
			    
	         catch (DBException e1) 
         	 {
                     e1.printStackTrace();
	          }
			
		    jlCast.setListData(coActorArray);
			        
						
	      }
}

Alles funktioniert wie geplant, nur beim löschen des letzten Elements bekomme mehrere Nullpointer Exceptions (unten). Die Zeile in meinem Code, die diese Exception auslöst ist, ist folgende, im oberen Code entspricht sie Zeile 22:

jlCast.setListData(coActorArray);

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
	at javax.swing.JList$4.getSize(JList.java:1666)
	at javax.swing.plaf.basic.BasicListUI.updateLayoutState(BasicListUI.java:1330)
	at javax.swing.plaf.basic.BasicListUI.maybeUpdateLayoutState(BasicListUI.java:1299)
	at javax.swing.plaf.basic.BasicListUI$Handler.valueChanged(BasicListUI.java:2612)
	at javax.swing.DefaultListSelectionModel.fireValueChanged(DefaultListSelectionModel.java:167)
	at javax.swing.DefaultListSelectionModel.fireValueChanged(DefaultListSelectionModel.java:147)
	at javax.swing.DefaultListSelectionModel.fireValueChanged(DefaultListSelectionModel.java:194)
	at javax.swing.DefaultListSelectionModel.changeSelection(DefaultListSelectionModel.java:388)
	at javax.swing.DefaultListSelectionModel.changeSelection(DefaultListSelectionModel.java:398)
	at javax.swing.DefaultListSelectionModel.removeSelectionIntervalImpl(DefaultListSelectionModel.java:559)
	at javax.swing.DefaultListSelectionModel.clearSelection(DefaultListSelectionModel.java:403)
	at javax.swing.JList.clearSelection(JList.java:2013)
	at javax.swing.JList.setModel(JList.java:1646)
	at javax.swing.JList.setListData(JList.java:1664)
	at pmdbproject.Controls.EditMovieWindow.actionPerformed(EditMovieWindow.java:583)
	at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
	at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
	at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
	at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
	at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
	at java.awt.Component.processMouseEvent(Component.java:6134)
	at javax.swing.JComponent.processMouseEvent(JComponent.java:3265)
	at java.awt.Component.processEvent(Component.java:5899)
	at java.awt.Container.processEvent(Container.java:2023)
	at java.awt.Component.dispatchEventImpl(Component.java:4501)
	at java.awt.Container.dispatchEventImpl(Container.java:2081)
	at java.awt.Component.dispatchEvent(Component.java:4331)
	at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4301)
	at java.awt.LightweightDispatcher.processMouseEvent(Container.java:3965)
	at java.awt.LightweightDispatcher.dispatchEvent(Container.java:3895)
	at java.awt.Container.dispatchEventImpl(Container.java:2067)
	at java.awt.Window.dispatchEventImpl(Window.java:2458)
	at java.awt.Component.dispatchEvent(Component.java:4331)
	at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
	at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
	at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
	at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
	at javax.swing.JList$4.getSize(JList.java:1666)
	at javax.swing.plaf.basic.BasicListUI.updateLayoutState(BasicListUI.java:1330)
	at javax.swing.plaf.basic.BasicListUI.maybeUpdateLayoutState(BasicListUI.java:1299)
	at javax.swing.plaf.basic.BasicListUI.getPreferredSize(BasicListUI.java:566)
	at javax.swing.JComponent.getPreferredSize(JComponent.java:1632)
	at javax.swing.ScrollPaneLayout.layoutContainer(ScrollPaneLayout.java:769)
	at java.awt.Container.layout(Container.java:1398)
	at java.awt.Container.doLayout(Container.java:1387)
	at java.awt.Container.validateTree(Container.java:1485)
	at java.awt.Container.validate(Container.java:1457)
	at javax.swing.RepaintManager.validateInvalidComponents(RepaintManager.java:670)
	at javax.swing.SystemEventQueueUtilities$ComponentWorkRequest.run(SystemEventQueueUtilities.java:127)
	at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
	at java.awt.EventQueue.dispatchEvent(EventQueue.java:597)
	at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
	at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
	at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
	at javax.swing.JList$4.getSize(JList.java:1666)
	at javax.swing.plaf.basic.BasicListUI.updateLayoutState(BasicListUI.java:1330)
	at javax.swing.plaf.basic.BasicListUI.maybeUpdateLayoutState(BasicListUI.java:1299)
	at javax.swing.plaf.basic.BasicListUI.paintImpl(BasicListUI.java:251)
	at javax.swing.plaf.basic.BasicListUI.paint(BasicListUI.java:227)
	at javax.swing.plaf.ComponentUI.update(ComponentUI.java:143)
	at javax.swing.JComponent.paintComponent(JComponent.java:763)
	at javax.swing.JComponent.paint(JComponent.java:1027)
	at javax.swing.JComponent.paintToOffscreen(JComponent.java:5122)
	at javax.swing.BufferStrategyPaintManager.paint(BufferStrategyPaintManager.java:277)
	at javax.swing.RepaintManager.paint(RepaintManager.java:1217)
	at javax.swing.JComponent._paintImmediately(JComponent.java:5070)
	at javax.swing.JComponent.paintImmediately(JComponent.java:4880)
	at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:803)
	at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:714)
	at javax.swing.RepaintManager.seqPaintDirtyRegions(RepaintManager.java:694)
	at javax.swing.SystemEventQueueUtilities$ComponentWorkRequest.run(SystemEventQueueUtilities.java:128)
	at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
	at java.awt.EventQueue.dispatchEvent(EventQueue.java:597)
	at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
	at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
	at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

Kann mir jemand weiterhelfen?

 

[Marco13]

Vielleicht ist der array 'null' ?

 

[Nizar1984]

Vielleicht ist der array 'null' ?

Hi,

Der Array coActorArray wird beim Löschen des letzten Listenelements tatsächlich null, und dies löst vermutlich die Exception aus.

Das problem ist, ich könnte das ja mittels einer if bedingung verhindern, dass der null array weiter verarbeitet werden kann. aber wie kann ich dann die JList so updaten, dass nach dem löschen des letzten eintrags nichts mehr in der liste ist, ohne dann den zuletzt leeren array zu übergeben?

 

[Marco13]

Ich weiß grad nicht, ob eine JList es "verträgt", wenn man ihr (nicht null sondern) einen leeren Array gibt ... müßte aber gehen

if (coActorArray==null)
{
    jlCast.setListData(new Actor[0]); 
}
else
{
    jlCast.setListData(coActorArray); 
}

Vielleicht noch etwas ... hübscher... je nach Geschmack:

if (coActorArray==null)
{
    jlCast.setListData(new String[]{"(none)"}); 
    jlCast.setEnabled(false);
}
else
{
    jlCast.setListData(coActorArray); 
    jlCast.setEnabled(true);
}

 

[Nizar1984]

Vielen Dank, so funkionierts!!