Example of saving XML to the Excel document file from a VSTO Excel Ribbon Addin

RibbonXMLPersistance.cs

public void AddCustomXmlPartToWorkbook()
{
    var workbook = Globals.ThisAddIn.Application.ActiveWorkbook;

    const string xmlString = "<?xml version=\"1.0\" encoding=\"utf-8\" ?>" +
                                "<employees xmlns=\"http://myapi.com\">" +
                                "<employee>" +
                                "<name>Karina Leal</name>" +
                                "<hireDate>1999-04-01</hireDate>" +
                                "<title>Manager</title>" +
                                "</employee>" +
                                "</employees>";

    Microsoft.Office.Core.CustomXMLPart employeeXMLPart = workbook.CustomXMLParts.Add(xmlString, System.Type.Missing);
}

public string RetrieveCustomXmlPartFromWorkbook()
{
    var workbook = Globals.ThisAddIn.Application.ActiveWorkbook;

    var retrievedXMLParts = workbook.CustomXMLParts.SelectByNamespace("http://myapi.com");

    var customXMLPart = retrievedXMLParts.Cast<CustomXMLPart>().FirstOrDefault() ;
    return customXMLPart != null ? customXMLPart.XML : String.Empty;
}

http://stackoverflow.com/questions/13567921/how-can-i-persist-data-for-an-excel-ribbon-addin-in-excel

http://stackoverflow.com/questions/13567921/how-can-i-persist-data-for-an-excel-ribbon-addin-in-excel