How to display picklist values based on Lookup value on VF page?

Question

I created a custom VF page to create custom object record. I have a Account lookup on page.

So whenever a user selects value from the lookup I would like to show dynamic picklist options on VF page by querying with LookupID for example I want to show names on dropdown, queried from selected lookup Id before saving the record.

Class:

public class createPriceRecord
{
    public Price__c price{get; set;}
    public Price__c priValue;
    public Id lookupId{get;set;}
    public Price__c ReqOpp;

    public createPriceRecord (ApexPages.StandardController controller) {
        price= (Price__c)controller.getRecord();
        stdCtrl=controller;
    }
    private ApexPages.StandardController stdCtrl;

    public void AccPopulated()
    {
        priValue= (Price__c)stdCtrl.getRecord();
    }

    public List<selectOption> getselectValues()
    {
        List<Prod__c> relatedprod = new List<Prod__c>();

        relatedprod = [Select Id,name from Prod__c where AccLookup__c.id =: priValue.Account__r.ID ]; // trying to get Account id from VF page

        List<SelectOption> Options = new List<SelectOption>();

        Options.add(new SelectOption('','-None-'));

        for(Prod__c prod:relatedprod)
        {
            Options.add(new SelectOption(prod.Id,prod.Name));
        }
        return Options;
    }

    public PageReference SaveRec(){

        price.Look_Up__c = lookupId;
        insert price;

        PageReference p=new PageReference('my.salesforce.com/'+price.Id);
        return p;

    }

}

Page :

<apex:page standardController="Price__c" extensions="createPriceRecord" tabStyle="Price__c">
 <apex:form >
    <apex:pageBlock title="Price Edit" mode="edit">
        <apex:pageBlockButtons>
            <apex:commandButton value="Save" action="{!SaveRec}"/>
        </apex:pageBlockButtons>

        <apex:pageBlockSection columns="2" title="Price Information">
            <apex:inputField value="{!price.AccountId}">
            <apex:actionSupport event="onchange" action="{!AccPopulated}" immediate="true" />
            </apex:inputfield>

            <apex:selectList value="{!lookupId}" title="Select" multiselect="false" size="1" >
            <apex:selectOptions value="{!selectValues}"/>
            </apex:selectList>

            <apex:inputField value="{!price.name}"/>
        </apex:PageBlockSection>
    </apex:pageBlock>
</apex:form >
</apex:page>

Answer 1

You have to use ActionSupport correctly to pass parameter to controller method and rerender the select list.

I have suggested following code.

1. Create a fieldValue variable which will store AccountId from UI
2. In AccPopulated() method capture fieldValue=price.AccountId;
3. In actionSupport reRender="selectListValues" which will refresh the list.

Visualforce

<apex:inputField id="accountId" value="{!price.AccountId}">
    <apex:actionSupport event="onchange" reRender="selectListValues" action="{!AccPopulated}"/>          
</apex:inputfield>

<apex:selectList value="{!lookupId}" title="Select" multiselect="false" size="1" id="selectListValues">
    <apex:selectOptions value="{!selectValues}"/>
</apex:selectList>

Controller

//fieldValue will be captured from UI
public String fieldValue {get; set;}
public createPriceRecord (ApexPages.StandardController controller) {
    price= (Price__c)controller.getRecord();
    fieldValue = priValue.Account__r.ID;
    stdCtrl=controller;
}

public void AccPopulated()   
{
      fieldValue = price.AccountId;        
      getselectValues();  
}

public List<selectOption> getselectValues()
{
    List<Prod__c> relatedprod = new List<Prod__c>();        
    relatedprod = [Select Id,name from Prod__c where AccLookup__c.id =:fieldValue ]; // trying to get Account id from VF page

    List<SelectOption> Options = new List<SelectOption>();
    Options.add(new SelectOption('','-None-'));
    for(Prod__c prod:relatedprod)
    {
        Options.add(new SelectOption(prod.Id,prod.Name));
    }
    return Options;
}