C-Sharp - Backgroundworker - Rückgabe - Verständnis

frm_WorkInProgress frmWIP = new frm_WorkInProgress(tblFilter, lstTables[2], lstTables[1]);
frmWIP.ShowDialog();

//  Loading Components
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

//  Namespace for the failed CI's form - Validator_Reloaded 
namespace Validator_Reloaded
{
    public partial class frm_WorkInProgress : Form
    {
        //  Define the tables that get importet
        DataTable tblCIs;
        DataTable tblCIService;
        DataTable tblServiceLists;

        //  Work in progress: Class
        public frm_WorkInProgress(DataTable tblCIs, DataTable tblCIService, DataTable tblServiceLists)
        {
            InitializeComponent();

            //  set the new createt tables to the same tables
            this.tblCIs = tblCIs;
            this.tblCIService = tblCIService;
            this.tblServiceLists = tblServiceLists;
        }

        //  define a new variable for the finished percent
        int percentFinished = 0;

        //  define datatables
        DataTable tblCont = new DataTable();
        DataTable tblServices = new DataTable();
        DataTable tblFailedCIs = new DataTable();

        //  Create Dataviews
        DataView dvFailedCIs = new DataView();
        DataView dvCIService;
        DataView dvServiceList;

        //  Create new Lists
        List<List<string>> lstCIs = new List<List<string>>();
        List<string> lstFailedCIs = new List<string>();
        List<string> lstCIServices = new List<string>();
        List<string> lstServices = new List<string>();
        List<string> lstContent = new List<string>();

        //  Create a new Array
        int arrColumnNr = { 0, 7, 9 };

        //  Load event
        private void _03_Validator_Progress_Load(object sender, EventArgs e)
        {
            // fill the the dataviews with the table CI's & tbl Service Lists 
            dvCIService = new DataView(tblCIs);
            dvServiceList = new DataView(tblServiceLists);

            //  foreach row in the CI table
            foreach (DataRow row in tblCIs.Rows)
            {
                //  set the lstContent as a new list
                lstContent = new List<string>();

                //  foreach integer in the Column Array
                foreach (int i in arrColumnNr)
                {
                    //  add a new row to the lstContent
                    lstContent.Add(row[i].ToString());
                }

                //  add the list to the CI - list
                lstCIs.Add(lstContent);
            }

            //  define the maximum from the pgbFortschritt - progressbar | as the lstCIs Count
            progressBar1.Maximum = lstCIs.Count;

            System.Windows.Forms.Application.DoEvents();

            //  Start the Backkground Worker
            worker.RunWorkerAsync(progressBar1.Value);
        }

        //  the Do Work event for the worker
        void worker_DoWork(object sender, DoWorkEventArgs e)
        {
            //  foreach list in list CIs
            foreach (List<string> list in lstCIs)
            {
                //  Search the table for the current CI
                dvCIService.RowFilter = "CI Like '" + list + "'";  

                //  add the Dataview to a table
                tblCont = dvCIService.ToTable();

                //  get a table with the Servicelist CIs
                dvServiceList.RowFilter = String.Format("convert(Customer, 'System.String') Like '" + list[1].ToString() + "' AND convert(Model, 'System.String') Like '" + list[2].ToString() + "'");  
                tblServices = dvServiceList.ToTable();

                //  Set the two lists as new string Lists
                lstCIServices = new List<string>();
                lstServices = new List<string>();

                //foreach row in in the table Content
                foreach (DataRow row in tblCont.Rows)
                {
                    //  add the first item in the current row to the list CIServices
                    lstCIServices.Add(row[1].ToString());
                }

                //  foreach row in the table Services
                foreach (DataRow row in tblServices.Rows)
                {
                    //  add the 3rd item in the row to the List
                    lstServices.Add(row[3].ToString());
                }

                //  If the lenght from the List CIServices not equal the Services List lenght
                if (lstCIServices.Count != lstServices.Count)
                {
                    //  Add the CI to the failed CI list
                    lstFailedCIs.Add(list);
                }
                else
                {
                    //  Check if the lists arent equal 
                    var a = lstCIServices.All(lstServices.Contains);

                    if (a == false)
                    {
                        //  if it isn't equal ad dit to the Failed CI list 
                        lstFailedCIs.Add(list);
                    }
                }

                //  Add another point to the progressbar
                percentFinished++;
                worker.ReportProgress(percentFinished);
            }

            //  Update the label with bonus information
            lblAnzeige.Text = "Fertig stellen...";  
            
            //  set the dvFailedCIs as New DataView
            dvFailedCIs = new DataView(tblCIs);

            //  Make Sure the string is empty
            string strCMD = "";  

            //  Check if the list with the failed CI's isn't 0 
            if (lstFailedCIs.Count >= 1)
            {
                //  Create a filter string for a Dataview rowfilter.
                strCMD = strCMD + "(CI IN ('" + lstFailedCIs + "' ";  

                //  add each item in the Failed CIs list into the strCMD
                foreach(string i in lstFailedCIs)
                {
                    strCMD = strCMD + ", '" + i + "'";  
                }
                strCMD = strCMD + "))";  
            }
            else
            {
                //  else add 2 Points to the progressbar
                percentFinished = percentFinished + 2;
            }

            //  generate a datatable with the wrong CI string
            dvFailedCIs.RowFilter = strCMD;
            tblFailedCIs = dvFailedCIs.ToTable();

            e.Result = tblFailedCIs;
        }

        //  Update event for the worker
        void worker_ProgressChanged(object sender, ProgressChangedEventArgs e)
        {
            progressBar1.Value = e.ProgressPercentage;
            lblAnzeige.Text = percentFinished.ToString() + " / " + lstCIs.Count.ToString();  
        }

        // Completet Event for Worker
        void worker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
            DataTable tblTest = (DataTable)e.Result;

            lblAnzeige.Text = "Completed!";  
            button1.Enabled = true;
        }
        //  Klick event for the button
        private void btn_Okay_Click(object sender, EventArgs e)
        {
            this.Close();
        }
    }