Reading the value of the cell, and with box

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Microsoft.Office.Tools.Ribbon;
//-----< using >-----------
using Microsoft.Office.Tools.Ribbon;
using Excel = Microsoft.Office.Interop.Excel;
using Office = Microsoft.Office.Core;
using Microsoft.Office.Tools.Excel;
//----</ using >------------

namespace ExcelAddIn5
{
    public partial class Ribbon1
    {
        private void Ribbon1_Load(object sender, RibbonUIEventArgs e)
        {

        }

        private void button1_Click(object sender, RibbonControlEventArgs e)
        {
            //< open Excel Worksheet >
            Excel.Worksheet activeWorksheet = Globals.ThisAddIn.Application.ActiveSheet;
            //< open Excel Worksheet >

            //< get Cell.Value >
            Excel.Range actCell = Globals.ThisAddIn.Application.ActiveCell;
            if (actCell.Value2 != null)
            {
                string sValue = actCell.Value2.ToString();
                string sText = actCell.Text;
                System.Windows.Forms.MessageBox.Show(sText);
            }
            //</ get Cell Value >
        }
    }
}