Question on populating a field based on 2 other fields

Question

Hi,
I am looking for a solution wherein I need to populate a field (say no of days) based on the other two fields selected by the user (say date from and date to). As soon as user selects the value on "date to" field, "no of days" field should be auto-populated as the value from "date to - date from". I have tried using setter and getter methods on all three field, set valuechangelistener on date to field, set auto submit to true and in the valuechangelistener event code, I am doing the calculations as mentioned in the below snippet.
public void onChangeDateTo(ValueChangeEvent evt){
this.dtDateTo= (java.util.Date)evt.getNewValue();
this.dtDateFrom = (java.util.Date)getDateFrom();//This is the getter method for date from field
System.out.println("onChangeDateTo "+ this.dtDateFrom+":"+this.dtDateTo);
if (evt.getNewValue() != null){
int intCalcNoOfDays = DateHelper.getBusinessDaysCount(this.getDateFrom(),this.getDateTo()) + 1;// my custom class which does the calculation
String strCalcNoOfDays = String.valueOf(intCalcNoOfDays);
System.out.println("strCalcNoOfDays "+strCalcNoOfDays);
this.setNoOfDays(strCalcNoOfDays);
I am getting NullPointerException while getting the value for date from (this.dtDateFrom). I have tried other approaches like attaching a binding to date from field, passing attributes etc but no luck. Can someone assist me in achieving this? Basically I need to populate one field automatically based on values entered on two other fields whenever tab event/user selects value on second field AND it shouldn't fire any other validations on the form (basically partial trigger).
Thanks very much for the help in advance.
Thanks
Shree

Answer 1

Thanks Lilly.
I don't have a backing bean associated with the page. I have managed bean instead. JSF source code snippet below
<?xml version='1.0' encoding='UTF-8'?>
<jsp:root xmlns:jsp="http://java.sun.com/JSP/Page" version="2.1" xmlns:f="http://java.sun.com/jsf/core"
xmlns:af="http://xmlns.oracle.com/adf/faces/rich" xmlns:h="http://java.sun.com/jsf/html">
<jsp:directive.page contentType="text/html;charset=UTF-8"/>
<f:view>
<af:document title="LMS" id="d1">
<af:messages id="m1"/>
<af:form id="f1">
<af:panelStretchLayout id="psl1" startWidth="160px">
<f:facet name="top">
<af:panelGroupLayout id="pgl1" layout="vertical" halign="center">
<af:panelFormLayout id="pfl1" rows="1" maxColumns="1">
<af:outputText value="LMS" id="ot1"
inlineStyle="color:Blue; font-family:'Times New Roman', 'Arial Black', times, Serif; font-size:175%; font-weight:bold; text-align:center;"/>
</af:panelFormLayout>
</af:panelGroupLayout>
</f:facet>
<f:facet name="bottom">
<af:panelGroupLayout id="pgl2"/>
</f:facet>
<f:facet name="center">
<af:panelGroupLayout layout="scroll" id="pgl4">
<af:outputText value="Dashboard" id="ot6"
inlineStyle="color:Green; font-size:150%; font-family:'Times New Roman', 'Arial Black', times, Serif; font-weight:bold; text-align:center;"
visible='#{clickActionHandlerBean.clickLink== "HOME"}'/>
<af:spacer width="10" height="10" id="s1"
visible='#{clickActionHandlerBean.clickLink== "HOME"}'/>
<af:spacer width="10" height="25" id="s5"
visible='#{clickActionHandlerBean.clickLink=="APPLY"}'/>
<af:panelFormLayout id="pfl2" rows="1" maxColumns="1"
visible='#{clickActionHandlerBean.clickLink=="APPLY"}'>
<af:selectOneChoice label="Type" id="soc1" showRequired="true"
immediate="true" value="#{bean1.type}">
<af:selectItem label="X1" value="X1" id="si1"/>
<af:selectItem label="X2" value="X2 id="si2"/>
<af:selectItem label="X3" value="X3" id="si3"/>
<af:selectItem label="X4 value="X4" id="si4"/>
</af:selectOneChoice>
</af:panelFormLayout>
<af:panelFormLayout id="pfl3" rows="1" maxColumns="3"
visible='#{clickActionHandlerBean.clickLink=="APPLY"}'>
<af:inputDate label=" Date From" id="id1"
rendered='true'
showRequired="true" inlineStyle="vertical-align:baseline;"
value="#{bean1.dateFrom}">
<af:convertDateTime pattern="dd-MMM-yyyy" secondaryPattern="MM/dd/yyyy"/>
</af:inputDate>
<af:inputDate label="Date To" id="id2"
rendered='true'
showRequired="true" value="#{bean1.dateTo}" partialTriggers="it1"
valueChangeListener="#{bean1.onChangeDateTo}"
autoSubmit="true">
<af:convertDateTime pattern="dd-MMM-yyyy" secondaryPattern="MM/dd/yyyy"/>
</af:inputDate>
<af:inputText label="No of Days" id="it1" columns="7" showRequired="true"
rendered="true" value="#{bean1.noOfDays}" maximumLength="2">
<af:validateRegExp pattern="[0-9]{1,10}"
messageDetailNoMatch="No of days can have only numbers"/>
</af:inputText>
</af:panelFormLayout>
<af:spacer width="10" height="50" id="s6"/>
<af:group id="g1">
<af:spacer width="250" height="10" id="s7"
visible='#{clickActionHandlerBean.clickLink=="APPLY"}'/>
<af:commandButton text="Save" id="cb1" partialSubmit="true" blocking="false"
immediate="false"
visible='#{clickActionHandlerBean.clickLink=="APPLY"}'
actionListener="#{bean1.ApplyButtonClicked}">
</af:commandButton>
<af:spacer width="20" height="10" id="s8"/>
<af:commandButton text="Cancel" id="cb2"
visible='#{clickActionHandlerBean.clickLink=="APPLY"}'/>
</af:group>
</af:panelGroupLayout>
</f:facet>
<f:facet name="start">
<af:panelGroupLayout id="pgl3" halign="left">
<p>
<af:outputText value="#{userinfo.userInfo.firstName}" id="otWel"
inlineStyle="color:Maroon;" rendered="false"/>
</p>
<af:spacer width="1" height="50" id="s2"/>
<p>
<af:commandLink text="Home" id="glHome" action="#{clickActionHandlerBean.showHomeRN}"/>
</p>
<p>
<af:commandLink text="Apply" id="glApply"
action="#{clickActionHandlerBean.showApplyRN}"/>
</p>
</af:panelGroupLayout>
</f:facet>
</af:panelStretchLayout>
</af:form>
</af:document>
</f:view>
</jsp:root>
Thanks
Shree