ThisAddIn.cs

using System;

namespace Example.ExcelAddin
{
    public partial class ThisAddIn
    {
        [Microsoft.VisualStudio.Tools.Applications.Runtime.Cached()]
        public String MyCachedData;

        private void ThisAddIn_Startup(object sender, System.EventArgs e)
        {
            StartCaching("MyCachedData");

            if (string.IsNullOrEmpty(MyCachedData))
                MyCachedData = "hello cache";
        }

        private void ThisAddIn_Shutdown(object sender, System.EventArgs e)
        {
        }

        #region VSTO generated code

        /// <summary>
        /// Required method for Designer support - do not modify
        /// the contents of this method with the code editor.
        /// </summary>
        private void InternalStartup()
        {
            this.Startup += new System.EventHandler(ThisAddIn_Startup);
            this.Shutdown += new System.EventHandler(ThisAddIn_Shutdown);
        }
        
        #endregion
    }
}