asynchronous wcf call ?

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C#

ASP.NET

i am calling a wcf service asynchronously its returning a srting value and i want to bind this to my text box txtEmpName.My problem is that wcf service is returning correct value in asyncallback but its not getting binded to textbox ? What modification i have to do in asyncallback ?

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
using System.ServiceModel;
using System.Threading;


public partial class AsynchronousCall : System.Web.UI.Page
{
    string EmpName = null;
    
    protected void Page_Load(object sender, EventArgs e)
    {
         
       
    }
    protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
    {
        int EmpNo = Convert.ToInt32(DropDownList1.SelectedValue);
         makeAysnCall(EmpNo);  
       
    }


    public void makeAysnCall (int EmpNo)
    {
    
     ServiceReference1.EmpNameServiceClient client = new ServiceReference1.EmpNameServiceClient();
        EndpointAddress endpointAddress = client.Endpoint.Address;
        BasicHttpBinding basicHttpBinding = new BasicHttpBinding();

        ServiceReference1.IEmpNameService iEmpNameService
      = new ChannelFactory<servicereference1.iempnameservice>(basicHttpBinding,  endpointAddress).CreateChannel();
        AsyncCallback asynCallBack = delegate(IAsyncResult result)
        {
             EmpName = iEmpNameService.EndgetEmpName(result);
             txtEmpName.Text = EmpName;
                                  
        };
        
        iEmpNameService.BegingetEmpName(EmpNo, asynCallBack, iEmpNameService);       
      }
}</servicereference1.iempnameservice>