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private async void btn4_Start_Click_2(object sender, RoutedEventArgs e)
        {
            XmlDocument doc = new XmlDocument();
            doc.Load("K:\\MAM\\DevExpress\\cs proj datei.v16.2.xml");

            Console.WriteLine("Nodes");
            foreach (XmlNode node in doc.DocumentElement.ChildNodes)
            {
                string text = node.Name; //or loop through its children as well
                Console.WriteLine("ItemGroup:" + text);
                foreach (XmlNode unterknoten in node)
                {
                    string text1 = unterknoten.Name; //or loop through its children as well
                    Console.WriteLine("Refernence:" + text1);

                    XmlAttribute idAttribute = aNode.Attributes[".v15.1."]; //ID Wert

                        if (idAttribute != null)
                        {

                            string currentValue = idAttribute.Value;


                            if (string.IsNullOrEmpty(currentValue))
                            {
                                idAttribute.Value = ".v15.4"; // ersetzen des neuen Wertes. 
                            }
                    
                }					

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XmlAttribute idAttribute = aNode.Attributes[".v15.1."]; //ID Wert