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https://issues.apache.org/jira/browse/WICKET-2442?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12833760#action_12833760
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Juergen Donnerstag commented on WICKET-2442:
--------------------------------------------
Looking at the code
97: IChoiceRenderer<T> renderer = getPalette().getChoiceRenderer();
98: StringBuffer modelStringBuffer = new StringBuffer();
99: Iterator<T> selection = getPalette().getModelCollection().iterator();
<<<< NPE
getPalette() obviously return a non-null value since it works in line 97. Thus
the problem must be getModelCollection() not returning a not null value. The
NPE can't be inside getModelCollection() since NPE would tell you.
... getModelCollection()
{
return (Collection<T>)getDefaultModelObject();
}
Consequently your model object is null.
> Palette, NullPointer
> --------------------
>
> Key: WICKET-2442
> URL: https://issues.apache.org/jira/browse/WICKET-2442
> Project: Wicket
> Issue Type: Bug
> Components: wicket-extensions
> Affects Versions: 1.4.1
> Reporter: Ulrik Hagberg
>
> When I try to add a Palette to a Page, I get an NullPointerException.
> Stacktrace:
> WicketMessage: Error attaching this container for rendering: [MarkupContainer
> [Component id = palette]]
> Root cause:
> java.lang.NullPointerException
> at
> org.apache.wicket.extensions.markup.html.form.palette.component.Recorder.initIds(Recorder.java:99)
> at
> org.apache.wicket.extensions.markup.html.form.palette.component.Recorder.onBeforeRender(Recorder.java:86)
> at org.apache.wicket.Component.internalBeforeRender(Component.java:1061)
> at org.apache.wicket.Component.beforeRender(Component.java:1095)
> at
> org.apache.wicket.MarkupContainer.onBeforeRenderChildren(MarkupContainer.java:1751)
> at org.apache.wicket.Component.onBeforeRender(Component.java:3863)
> at
> org.apache.wicket.extensions.markup.html.form.palette.Palette.onBeforeRender(Palette.java:191)
> at org.apache.wicket.Component.internalBeforeRender(Component.java:1061)
> at org.apache.wicket.Component.beforeRender(Component.java:1095)
> at
> org.apache.wicket.MarkupContainer.onBeforeRenderChildren(MarkupContainer.java:1751)
> at org.apache.wicket.Component.onBeforeRender(Component.java:3863)
> at org.apache.wicket.Component.internalBeforeRender(Component.java:1061)
> at org.apache.wicket.Component.beforeRender(Component.java:1095)
> at
> org.apache.wicket.MarkupContainer.onBeforeRenderChildren(MarkupContainer.java:1751)
> at org.apache.wicket.Component.onBeforeRender(Component.java:3863)
> at org.apache.wicket.Page.onBeforeRender(Page.java:1501)
> at org.apache.wicket.Component.internalBeforeRender(Component.java:1061)
> at org.apache.wicket.Component.beforeRender(Component.java:1095)
> at org.apache.wicket.Component.prepareForRender(Component.java:2232)
> at org.apache.wicket.Component.prepareForRender(Component.java:2269)
> at org.apache.wicket.Page.renderPage(Page.java:893)
> at
> org.apache.wicket.request.target.component.BookmarkablePageRequestTarget.respond(BookmarkablePageRequestTarget.java:262)
> at
> org.apache.wicket.request.AbstractRequestCycleProcessor.respond(AbstractRequestCycleProcessor.java:105)
> at
> org.apache.wicket.RequestCycle.processEventsAndRespond(RequestCycle.java:1258)
> at org.apache.wicket.RequestCycle.step(RequestCycle.java:1329)
> at org.apache.wicket.RequestCycle.steps(RequestCycle.java:1428)
> at org.apache.wicket.RequestCycle.request(RequestCycle.java:545)
> at org.apache.wicket.protocol.http.WicketFilter.doGet(WicketFilter.java:456)
> at
> org.apache.wicket.protocol.http.WicketFilter.doFilter(WicketFilter.java:289)
> at
> org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
> at
> org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
> at
> org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
> at
> org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
> at
> org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
> at
> org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
> at
> org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
> at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
> at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:849)
> at
> org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
> at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:454)
> at java.lang.Thread.run(Thread.java:619)
> Code:
> public class HomePage extends WebPage {
> public HomePage() {
> Form _form = new Form("form");
> add(_form);
> List<ChoiceModelObject> _availableChoices = new
> ArrayList<ChoiceModelObject>();
> _availableChoices.add(new ChoiceModelObject(0, "a"));
> _availableChoices.add(new ChoiceModelObject(1, "b"));
> _availableChoices.add(new ChoiceModelObject(2, "c"));
> _availableChoices.add(new ChoiceModelObject(3, "d"));
> ChoiceRenderer<ChoiceModelObject> _choiceRenderer = new
> ChoiceRenderer<ChoiceModelObject>() {
> @Override
> public Object getDisplayValue(ChoiceModelObject
> choiceModelObject) {
> return choiceModelObject.getName();
> }
> @Override
> public String getIdValue(ChoiceModelObject modelObject, int i) {
> return String.valueOf(modelObject.getId());
> }
> };
> _form.add(new Palette("palette", new ListModel(), new
> CollectionModel(_availableChoices), _choiceRenderer, 10, true));
> }
> class ChoiceModelObject implements Serializable {
> private int id;
> private String name;
> public ChoiceModelObject() {
> }
> private ChoiceModelObject(int id, String name) {
> this.id = id;
> this.name = name;
> }
> public int getId() {
> return id;
> }
> public void setId(int id) {
> this.id = id;
> }
> public String getName() {
> return name;
> }
> public void setName(String name) {
> this.name = name;
> }
> }
> }
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