[SalesForce] Lookup Filter Based on Selected Picklist Value Using Apex and Visualforce

I have changed the below controller. I initially didn't see that you're not calling any method from the apex:actionSupport tag. I have changed the below code (Apex / VF) and added some comments.

public with sharing class DynamicCasesExtension {

    public Case c { get; set; }
    public String objectName { get; set; }
    public List<String> objectFields { get; set; }
    public List<Case> SObjectListToShow { get; set; }

    public DynamicCasesExtension(){
        objectName = 'Case';
        //set the status to the value you need. In your case I assume it is coming in as a parameter. This is to be set only for the first load. 
        c.Status = ApexPages.currentPage().getParameters().get('c.Status');
        //SObjectListToShow = getSObjectList();
        generateList();
    }

    // a new method which will be called everytime the value in the picklist is changed
    public void generateList() {
        SObjectListToShow = caseSObjectList();
    }

    // Getting field list for the sObject. Changed the name of the method.
    public List<Case> caseSObjectList(){
        .
        .
        .
        //Change it to c.Status so that it gets set to the value selected from the page.
        String caseStatus = c.Status;
        .
        .
        .
    }

}

VF Page:

<apex:actionSupport event="onchange" rerender="result" action="{!generateList}"/>

Let me answer my question. It is possible using meta data describe pagelayout method.

<apex:outputPanel id="zoneFilter" layout="none">                          
    <h2 class="zoneLabel">Zone </h2> 
    <select title="Choose a Zone" style="width:22%;"  onchange="$('#zoneHidden input:first-child').val(this.value); changeDependentList(this.options[this.selectedIndex].innerHTML);">
            <option value="{!strZoneId}">{!strZoneName}</option>
                <apex:repeat id="repZone" value="{!lstZone}" var="objZone"  >                  
                    <apex:outputPanel id="optionZone" rendered="{!LOWER(objZone['label']) != LOWER(strZoneName)}" layout="none">
                        <option value="{!objZone['value']}">{!objZone['label']}</option>
                    </apex:outputPanel>
                </apex:repeat>
            </option>
    </select> 
    <span id="zoneHidden"><apex:inputHidden value="{!strZoneId}" /></span>         
</apex:outputPanel>

<apex:outputPanel id="categoryFilter" layout="none">  
    <h2>Category </h2>
    <select title="Choose a Categories" id="category" style="width:22%;"  onchange="$('#categoryHidden input:first-child').val(this.value);">

    </select>  
    <span id="categoryHidden"><apex:inputHidden value="{!strCategoryName}" /></span>  
</apex:outputPanel>              

<apex:outputPanel id="statusFilter" layout="none">           
    <h2 class="statusLabel">Status </h2>      
    <select title="Choose a Status"  id="status" style="width:22%;" onchange="$('#statusHidden input:first-child').val(this.value);"  >

    </select>  
    <span id="statusHidden"><apex:inputHidden value="{!strStatusName}" /></span>
</apex:outputPanel>  

<script>

    recordTypeMap = new Array();
    var recordTypeToStatus = [];
    var recordTypeToCategory = [];
    onloadPage();           

    function onloadPage()
    {
        sforce.connection.sessionId = '{!$Api.Session_ID}';
        // here in array we can send Record type Ids but it was giving some time wrong result , so blank array give result for all available //RecordType detail
        //result =  sforce.connection.describeLayout('Idea', new Array('099394343400034'));
        result =  sforce.connection.describeLayout('Idea', new Array());

        recordTypeName = new Array();
        recordTypeMap = result.recordTypeMappings;

        recordTypeMap.forEach(function(obj){
            recordTypeName.push(obj.name.substring(0,obj.name.indexOf(':')).toUpperCase());
        });

        recordTypeName.pop();
        recordTypeName.push('ALL');

        for(i=0;i<recordTypeMap.length;i++)
            recordTypeToStatus.push({'name':recordTypeName[i],'status': getName(recordTypeMap[i].picklistsForRecordType[1])});

        for(i=0;i<recordTypeMap.length;i++)
            recordTypeToCategory.push({'name':recordTypeName[i],'categories': getName(recordTypeMap[i].picklistsForRecordType[0])});

        changeDependentList('{!strZoneName}');

    }

    function getName(MainList)
    {
        var modiflist = new Array();
        if(MainList.picklistValues.length == undefined)
            modiflist.push(MainList.picklistValues.label);
        else
        {
            MainList.picklistValues.forEach(function(obj){
                modiflist.push(obj.label);
            });
        }
        return modiflist;
    }

    function changeDependentList(zoneName)
    {
        console.log(recordTypeName);
        console.log(zoneName.toUpperCase());

        indexToChange = recordTypeName.indexOf(zoneName.toUpperCase());

        if(indexToChange != -1){

            var statusList = recordTypeToStatus[indexToChange];

            console.log($('#statusHidden input:first-child').val());
            var currentStatus = $('#statusHidden input:first-child').val();
            console.log(statusList.status);

            $('#status').empty(); //removing old childs
            var $ele1 = $('#status');



            if(statusList.status.indexOf(currentStatus) == -1)  
            {
                $ele1.append($('<option value="All">All</option>'));
            }
            else
                $ele1.append($('<option value='+currentStatus+'>'+currentStatus+'</option>'));


            statusList.status.forEach(function(statusToAdd){

                $ele1                          
                   .append($("<option></option>")
                    .attr("value", statusToAdd)
                    .text(statusToAdd)
                   );
            });


            var categoryList = recordTypeToCategory[indexToChange];

            $('#category{!id}').empty(); //removing old childs
            var $ele2 = $('#category');
            $ele2.append($('<option value="All">All</option>'));

            categoryList.categories.forEach(function(statusToAdd){
                $ele2                          
                   .append($("<option></option>")
                    .attr("value", statusToAdd)
                    .text(statusToAdd)
                   );
            });
        }

    }


</script>