Salesforce: Attempt to de-reference a null object - salesforce

Question

I've searched and found several articles about this error, but I'm new to APEX and Visualforce and so I can't figure out how to apply the solutions to what I'm working on. Any help would be appreciated. What I'm trying to do in the code below is create a visualforce page embedded on Opportunity records that displays 2 multi-select picklists, one being dependent on the choice(s) picked in the first.
public class WatermelonOppController {
//added an instance varaible for the standard controller
private ApexPages.StandardController controller {get; set;}
// the actual opportunity
private Opportunity o;
public String[] parentPicklistVal {public get; public set;}
public String[] childMultiPicklistVal {public get; public set;}
public String childSinglePicklistVal {public get; public set;}
// maps to hold your dependencies between picklists
private Map<String, List<String>> parentDepMap;
private Map<String, List<String>> childDepMap;
private String[] parentOpts = new String[] { 'parent option 1', 'parent option 2' };
private String[] childMultiOpts = new String[] { 'child multi 1', 'child multi 2', 'child multi 3' };
//private String[] childSingleOpts = new String[] { 'child single 1', 'child single 2', 'child single 3' };
public WatermelonOppController(ApexPages.StandardController controller) {
//initialize the stanrdard controller
this.controller = controller;
//this.o = (Opportunity)controller.getRecord();
}
public WatermelonOppController() {
// init dependency maps
parentDepMap = new Map<String, List<String>>();
// childDepMap = new Map<String, List<String>>();
// pick which child options to display for which parent value
parentDepMap.put(parentOpts[0], (new String[]{childMultiOpts[0], childMultiOpts[1]}));
parentDepMap.put(parentOpts[1], (new String[]{childMultiOpts[1], childMultiOpts[2]}));
// pick which single-select options to display for which child value
//childDepMap.put(childMultiOpts[0], (new String[]{childSingleOpts[0], childSingleOpts[2]}));
//childDepMap.put(childMultiOpts[1], (new String[]{childSingleOpts[1], childSingleOpts[2]}));
//childDepMap.put(childMultiOpts[2], childSingleOpts); // or if you want to show them all?
}
public List<SelectOption> getParentPicklistOptions() {
List<SelectOption> selectOpts = new List<SelectOption>();
for ( String s : parentOpts )
selectOpts.add(new SelectOption(s, s));
return selectOpts;
}
public List<SelectOption> getChildMultiPicklistOptions() {
List<SelectOption> selectOpts = new List<SelectOption>();
if ( parentPicklistVal != null && parentPicklistVal.size() > 0 ) {
// build a set of values to avoid dupes, since there may be overlapping dependencies
Set<String> possibleOpts = new Set<String>();
for ( String val : parentPicklistVal )
possibleOpts.addAll(parentDepMap.get(val));
for ( String s : possibleOpts )
selectOpts.add(new SelectOption(s, s));
}
return selectOpts;
}
/*
public List<SelectOption> getChildSinglePicklistOptions() {
List<SelectOption> selectOpts = new List<SelectOption>();
if ( childMultiPicklistVal != null && childMultiPicklistVal.size() > 0 ) {
// build a set of values to avoid dupes, since there may be overlapping dependencies
Set<String> possibleOpts = new Set<String>();
for ( String val : childMultiPicklistVal )
possibleOpts.addAll(childDepMap.get(val));
for ( String s : possibleOpts )
selectOpts.add(new SelectOption(s, s));
}
return selectOpts;
}
*/
public PageReference actionUpdatePicklistVals() {
// this doesn't really need to do anything, since the picklists should be updated when their getters call after returning
return null;
}
}
And the Visualforce page:
<apex:page standardController="Opportunity" extensions="WatermelonOppController">
<apex:form >
<apex:outputPanel id="panel1">
<apex:selectList value="{!parentPicklistVal}" multiselect="true" size="3">
<apex:selectOptions value="{!parentPicklistOptions}" />
<apex:actionSupport event="onchange" action="{!actionUpdatePicklistVals}" rerender="panel1" />
</apex:selectList>
<apex:selectList value="{!childMultiPicklistVal}" multiselect="true" size="3">
<apex:selectOptions value="{!childMultiPicklistOptions}" />
<apex:actionSupport event="onchange" action="{!actionUpdatePicklistVals}" rerender="panel1" />
</apex:selectList>
</apex:outputPanel>
</apex:form>

Answer 1

You should move all your logic from default contructor to the parameterized constructor. Since the class is an extension, it's parameterized contructor with Standard Controller is being called.