Set user permissions to SPList

Sometimes I need to set permissions for special SPUser to special SPList.
Therefore , I developed winform solution, which helps me.

First of all, I use BackgroundWorker just to execute the operation on a separated thread.
Second, I aggregate fields from the form, which help me to bring a relevant data:
SiteURL - www.contoso.com
List - myList
ItemField - SPField("Display Name") For example item["ModifiedBy"]
ItemField Text - For example item["ModifiedBy"] = "Victor"
User - I use SPWeb.EnsureUser

 using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using Microsoft.SharePoint;

namespace GivenPermissions
{
    public partial class Form1 : Form
    {

        BackgroundWorker bg2 = new BackgroundWorker();

        public Form1()
        {
            InitializeComponent();
        }

        private void btnRun_Click(object sender, EventArgs e)
        {
            bg2.DoWork += new DoWorkEventHandler(bg2_DoWork);
            bg2.ProgressChanged += new ProgressChangedEventHandler(bg2_ProgressChanged);
            bg2.RunWorkerAsync();
        }

        private void bg2_ProgressChanged(object sender,
          ProgressChangedEventArgs e)
        {

        }

        
      

        void bg2_DoWork(object sender, DoWorkEventArgs e)
        {
            try
            {
                using (SPSite site = new SPSite(txtSiteUrl.Text))
                {
                    using (SPWeb web = site.OpenWeb())
                    {

                        SPList list = web.Lists[txtList.Text];

                        SPQuery query = new SPQuery();
                        query.ViewAttributes = "Scope=\"Recursive\"";


                        SPListItemCollection col = list.GetItems(query);

                        foreach (SPListItem item in col)
                        {
                            if (item[txtItemField.Text] != null && string.Compare(item[txtItemField.Text].ToString(), txtItemFielText.Text) == 0)
                            {
                                

                                    SPUser user = web.EnsureUser(txtUser.Text); 
                                    SPRoleType roleType = SPRoleType.Contributor;


                                    SPRoleAssignment roleAssignment = new SPRoleAssignment((SPPrincipal)user);
                                    SPRoleDefinition roleDefinition = item.Web.RoleDefinitions.GetByType(roleType);

                                    roleAssignment.RoleDefinitionBindings.Add(roleDefinition);
                                    item.RoleAssignments.Add(roleAssignment);

                                    item.Update();
                                
                            }
                        }


                    }
                }




                if (txtMessage.InvokeRequired)
                {
                    txtMessage.Invoke(new MethodInvoker(delegate
                    {


                        txtMessage.AppendText("DONE ! ! !");



                    }));
                }
            }
            catch (Exception ex)
            {
                if (txtMessage.InvokeRequired)
                {
                    txtMessage.Invoke(new MethodInvoker(delegate
                    {

                        txtMessage.AppendText(ex.Message + "\n" + ex.StackTrace);

                    }));
                }
            }



        }
    }
}