using pre & post images

using System.Collections.Generic;
//# CRM 2011: Using PRe & Post Images
using Microsoft.Xrm.Sdk;
using Microsoft.Xrm.Sdk.Query;
using System.ServiceModel;

namespace TestCompany.CRM.Plugin
{

    public class officeUpdate : IPlugin
    {
        public void Execute(IServiceProvider serviceProvider)
        {
            IPluginExecutionContext context;
            IOrganizationServiceFactory factory;
            IOrganizationService service;
            Entity PreImage;
            Entity PostImage;

            try
            {
                context = (IPluginExecutionContext)serviceProvider.GetService(typeof(IPluginExecutionContext));
                factory = (IOrganizationServiceFactory)serviceProvider.GetService(typeof(IOrganizationServiceFactory));
                service = factory.CreateOrganizationService(context.UserId);

                PreImage = (Entity)context.PreEntityImages["PreUpdateImage"];
                PostImage = (Entity)context.PostEntityImages["PostUpdateImage"];

                int _preOfficestatusVal = 0;
                int _postOfficestatusVal = 0;

                if (PreImage.Contains("new_officestatus"))
                {
                    _preOfficestatusVal = ((OptionSetValue)PreImage["new_officestatus"]).Value;
                }

                if (PostImage.Contains("new_officestatus"))
                {
                    _postOfficestatusVal = ((OptionSetValue)PostImage["new_officestatus"]).Value;
                }

                if ((_preOfficestatusVal == 100000002) && (_postOfficestatusVal == 100000001))
                {

                    // Logic for - Sub converted to Regional

                }

            }
            catch (FaultException e)
            {
                throw e;
            }
            finally
            {
                service = null;
                factory = null;
                context = null;
                PreImage = null;
                PostImage = null;
            }
        }
    }
}