ajax and p:picklist (PrimeFaces)

[massimo tarantelli]

Hello guys, here the issue:
I need to update the disable attribute of a commandButton based of the number of item in the picklist target, in particular if the target size is 0 the button must be disabled.
here my code (i'm using PrimeFaces 3.4):
Face:
<h:form id="skGruppo"> <p:pickList id="pickList" value="#{gruppo.grPick}" ... <f:ajax execute="pickSize" render="Button" event="transfer" /> </p:pickList> <h:inputHidden id="pickSize" value="#{gruppo.pickSize}" /> <p:commandButton ajax="true" id="button" disabled="#{gruppo.pickSize==0}" .../>

Bean:

public void setPickSize(int pickSize) {       
        this.pickSize = this.pick.getTarget().size(); //set the value of pickSize
    }

The idea was to use the setter method of the pickSize component in a non-ortodox way...
So, when an user transfer an item, the ajax will execute the hidden inputText trought its setter that in turn will set the size value in the pickSize, and finally it will change the value of the disabled attribute of the button.
...I have this is the track error:
any suggestion? thanks guys.

java.lang.NullPointerException
   at org.primefaces.component.picklist.PickList.populateModel(PickList.java:421)
   at org.primefaces.component.picklist.PickList.queueEvent(PickList.java:401)
   at com.sun.faces.renderkit.html_basic.AjaxBehaviorRenderer.decode(AjaxBehaviorRenderer.java:111)
   at javax.faces.component.behavior.ClientBehaviorBase.decode(ClientBehaviorBase.java:132)
   at org.primefaces.renderkit.CoreRenderer.decodeBehaviors(CoreRenderer.java:329)
   at org.primefaces.component.picklist.PickListRenderer.decode(PickListRenderer.java:50)
   at javax.faces.component.UIComponentBase.decode(UIComponentBase.java:787)
   at javax.faces.component.UIInput.decode(UIInput.java:757)
   at javax.faces.component.UIComponentBase.processDecodes(UIComponentBase.java:1181)
   at javax.faces.component.UIInput.processDecodes(UIInput.java:662)
   at com.sun.faces.context.PartialViewContextImpl$PhaseAwareVisitCallback.visit(PartialViewContextImpl.java:506)
   at com.sun.faces.component.visit.PartialVisitContext.invokeVisitCallback(PartialVisitContext.java:183)
   at javax.faces.component.UIComponent.visitTree(UIComponent.java:1590)
   at javax.faces.component.UIComponent.visitTree(UIComponent.java:1601)
   at javax.faces.component.UIComponent.visitTree(UIComponent.java:1601)
   at javax.faces.component.UIForm.visitTree(UIForm.java:344)
   at javax.faces.component.UIComponent.visitTree(UIComponent.java:1601)
   at javax.faces.component.UIComponent.visitTree(UIComponent.java:1601)
   at com.sun.faces.context.PartialViewContextImpl.processComponents(PartialViewContextImpl.java:376)
   at com.sun.faces.context.PartialViewContextImpl.processPartial(PartialViewContextImpl.java:252)
   at javax.faces.context.PartialViewContextWrapper.processPartial(PartialViewContextWrapper.java:183)
   at javax.faces.component.UIViewRoot.processDecodes(UIViewRoot.java:931)
   at com.sun.faces.lifecycle.ApplyRequestValuesPhase.execute(ApplyRequestValuesPhase.java:78)
   at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
   at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:118)
   at javax.faces.webapp.FacesServlet.service(FacesServlet.java:593)
   at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1542)
   at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:343)
   at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:217)
   at org.primefaces.webapp.filter.FileUploadFilter.doFilter(FileUploadFilter.java:79)
   at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:256)
   at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:217)
   at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:279)
   at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
   at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:655)
   at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:595)
   at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:161)
   at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:331)
   at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:231)
   at com.sun.enterprise.v3.services.impl.ContainerMapper$AdapterCallable.call(ContainerMapper.java:317)
   at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:195)
   at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:849)
   at com.sun.grizzly.http.ProcessorTask.doProcess(ProcessorTask.java:746)
   at com.sun.grizzly.http.ProcessorTask.process(ProcessorTask.java:1045)
   at com.sun.grizzly.http.DefaultProtocolFilter.execute(DefaultProtocolFilter.java:228)
   at com.sun.grizzly.DefaultProtocolChain.executeProtocolFilter(DefaultProtocolChain.java:137)
   at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:104)
   at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:90)
   at com.sun.grizzly.http.HttpProtocolChain.execute(HttpProtocolChain.java:79)
   at com.sun.grizzly.ProtocolChainContextTask.doCall(ProtocolChainContextTask.java:54)
   at com.sun.grizzly.SelectionKeyContextTask.call(SelectionKeyContextTask.java:59)
   at com.sun.grizzly.ContextTask.run(ContextTask.java:71)
   at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:532)
   at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:513)
   at java.lang.Thread.run(Thread.java:722)

[Tim Holloway]

You're doing this the hard way. The hidden control is not going to gain you anything.

You're also not defining the selectItems properly for the pickList. Unfortunately, you didn't include the definitions, and the stacktrace error messages for dropdown list-style controls are famously useless, so we'll need specific data.

[massimo tarantelli]

thanks for the answer, i have sorted out the problem in this way:
<p:pickList ...> <p:ajax event="transfer" listener="#{gruppo.onTransfer}" update="button" /> ... </p:pickList> <p:commandButton ajax="true" id="button" disabled="#{gruppo.pickSize==0}" .../>

public void onTransfer() {       
     pickSize = pick.getTarget().size();
}

ajax now works.
Anyway it evaluates the target size before the transfer, so it's always one click shifted...
how can I sort out it?