C#

SmtpClient client = new SmtpClient("smtp.gmail.com");
client.Port = 587;
client.EnableSsl = true;
client.Credentials = new System.Net.NetworkCredential("username@gmail.com", "password");

MailMessage msg;
MailAddress from;
MailAddress to;

from = new MailAddress("From Email Address", "my name here", System.Text.Encoding.UTF8);
to = new MailAddress("To Email Address");

msg = new MailMessage(from, to);
msg.Body = txtBody.Text;
msg.Body += Environment.NewLine;
msg.BodyEncoding = System.Text.Encoding.UTF8;
msg.Subject = txtSubject.Text;
msg.SubjectEncoding = System.Text.Encoding.UTF8;
client.Send(msg);
msg.Dispose();

[Serializable]
public class _ModelBase
{
    public Guid Id { get; set; }
    public string Caption { get; set; }
    public string Description { get; set; }
    public bool IsActive { get; set; }
    public int Sequence { get; set; }
    public ImageSource Image { get; set; }
}

[Serializable]
public class FolderModel : _ModelBase
{
    public List<FolderModel> Folders { get; set; }
    public List<FileModel> Files { get; set; }
    public bool IsExpanded { get; set; }

    public FolderModel()
    {
        Folders = new List<FolderModel>();
        Files = new List<FileModel>();
    }
}

[Serializable]
public class FileModel : _ModelBase
{
    public string FileName { get; set; }
}

private void saveAppDataToFile()
{
    using (TextWriter textWriter = new StreamWriter(xmlDataFile))
    {
        XmlSerializer serializer = new XmlSerializer(typeof(FolderModel));
        serializer.Serialize(textWriter, Folders);
        textWriter.Close();
    }
}

"There was an error generating the XML document."

"Unable to cast object of type 'System.Collections.Generic.List`1[MyApp.Models.FolderModel]' to type 'MyApp.Models.FolderModel'"}