Add These line of code in your button click event in last:
if (File.Exists(filename))
{
DataSet flatDataSet = new DataSet();
flatDataSet.ReadXml(filename);
DataTable table = flatDataSet.Tables[0];
dataGridKunden.DataSource = table;
}
However, your version of XmlTextWriter will overwrite the xml file. Thus, when you click on button you will see only the latest added row. Instead you can use below code in your button click event:
private void btnAddKunde_Click(object sender, EventArgs e)
{
if (!Directory.Exists(folder))
{
Directory.CreateDirectory(folder);
}
if (!File.Exists(filename))
{
using (File.Create(filename))
{}
}
XElement xmlNode = new XElement("Kundenverwaltung",
new XElement("KundenNr", txtKundenNr.Text),
new XElement("Nachname", txtKundeNachname.Text),
new XElement("Vorname", txtKundeVorname.Text),
new XElement("Adresse", txtKundeAdresse.Text),
new XElement("Ort", txtKundeOrt.Text),
new XElement("Telefon", txtKundeTel.Text),
new XElement("Mail", txtKundeMail.Text)
);
XElement xmlFile;
try
{
xmlFile = XElement.Load(filename);
xmlFile.Add(xmlNode);
}
catch (XmlException)
{
xmlFile = new XElement("Customers", xmlNode);
}
xmlFile.Save(filename);
DataSet flatDataSet = new DataSet();
flatDataSet.ReadXml(filename);
DataTable table = flatDataSet.Tables[0];
dataGridKunden.DataSource = table;
}