Getter Setter between two Visualforce pages

Question

I am confused how to use to getter setter in the situation of two Visualforce pages having different extensions.

1 VF Page(Main Page): This page calls Opportunity as Standard Controller and having two Extensions = Ext1, Ext2. I have a inputTextArea field where it has a lookup. On the click of the Lookup page(Second VF Page - LookupPage) user search for Employee records(custom object having SF and Non SF user list) and select multiple employees through a checkbox. On the click of the OK button in the lookup page it does gets all the Employee Names through Ext2. Till this point I am fine but I am confused how to retain the EmployeeNames from Ext2 and populate in the InputTextArea field which is on the First Page?

Page 1

<apex:page standardController="Opportunity" extensions="Ext1,Ext2" tabStyle="Opportunity" >
<apex:form id="form_Upload">
 <apex:pageBlockSection title="Email Recipients" columns="2">
                <apex:inputHidden value="{!allSelectedEmpIds}" id="targetId" />
                <apex:pageBlockSectionItem >
                    <apex:outputLabel value="Email To List" for="ToList"/>
                    <apex:outputPanel >
                        <apex:inputTextarea id="empNames" value="{!empName}" onfocus="this.blur()" disabled="false"/><a href="#" onclick="openLookupPopup(); return false">Lookup</a>---This is place where I want to get the Employee Names--
                    </apex:outputPanel>
                </apex:pageBlockSectionItem>
 </apex:form>
</apex:page>

Extension

public class Ext1{

    public String emailToList {get;set;}
    public String emailCcList {get;set;}
    public String emailBccList {get;set;}
    private final Opportunity opp {get;set;} 


    public Ext1(ApexPages.StandardController standardController) {
         this.opp = (Opportunity)standardController.getRecord();    
    }}

    public with sharing class Ext2{   public List<employeeWrapper> employeeList {get;set;}
    public String allSelectedEmpIds{get;set;}
    public String empName{get;set;} // This is the one I want to return to Main Page
    public boolean canLookup {get;set;}
    public String searchString{get;set;}
    private final Opportunity opp;
public void processSelected(){
        //PageReference np;
        allSelectedEmpIds = '';
        empName = '';
        for (employeeWrapper eEmp: employeeList) {
            System.debug('checkbox selected'+ eEmp.isSelected);
            if(eEmp.isSelected){
                allSelectedEmpIds += ';'+eEmp.employee.Id;
                empName += ';'+eEmp.employee.FullName__c;
            }/*else{
                allSelectedEmpIds += ';'+eEmp.employee.Id;
            } */

        }
}

Page 2

<apex:page id="employeeLookupPage" controller="Ext2" showHeader="false">
<apex:form >
        <apex:pageBlock title="Employee List" id="employeblock">
        <apex:pageBlockSection id="Section" showheader="false" columns="1">
                <!--apex:pageblocksectionitem id="SectionItem" >
                    <apex:outputLabel value="First Name or Last Name Search" for="searchStringPanel" style="font-weight:Bold;padding-right:10px;" />
                    <apex:outputPanel id="searchStringPanel"-->
                        <apex:inputText id="srchString" value="{!searchString}"/>
                        <apex:commandButton title="Go!" value="Go!" reRender="employeePanel" action="{!search}"/>
                    <!--/apex:outputPanel>
                </apex:pageblocksectionitem-->
            </apex:pageBlockSection>
            <apex:outputPanel id="employeePanel">
                <apex:pageBlock id="employeeBlock">
                    <apex:inputHidden value="{!allSelectedEmpIds}" id="targetId" />
                    <apex:inputHidden value="{!empName}" id="namefield" />
                    <apex:pageBlockTable value="{!employeeList}" var="empNames">
                        <apex:column >
                            <apex:inputCheckbox value="{!e.isSelected}" id="selectedEmp"/>
                        </apex:column>
                        <apex:column id="fname" >
                            <apex:facet name="header">First Name</apex:facet>
                            <apex:outputText value="{!e.employee.First_Name__c}"/>
                        </apex:column>
                        <apex:column headerValue="Last Name">
                            <apex:outputText value="{!e.employee.Last_Name__c}"/>
                        </apex:column>
                        <apex:column headerValue="Email">
                            <apex:outputText value="{!e.employee.Email__c}"/>
                        </apex:column>
                    </apex:pageBlockTable>
                </apex:pageBlock>
            </apex:outputPanel>
            <apex:pageBlockButtons location="bottom">
                <div align="Right" draggable="false">
                    <apex:commandButton value="Ok" action="{!processSelected}" />
                    <apex:commandButton value="Cancel" onclick="window.top.close()" />
                </div>
            </apex:pageBlockButtons>
        </apex:pageBlock>
</apex:page>

Answer 1

To create an StandardController extension you need to define constructor with StanardController as an argument.

public Ext2(ApexPages.StandardController standardController) {
         this.opp = (Opportunity)standardController.getRecord();    
    }

2nd thing, after closing the popup window, I think you are not refreshing the calling page, that's why it is not taking empNames and you are preparing those concatenated values on server side.

So you need to rerender page with "form_Upload" to retrieve updated values.