\

<WindowsSdkPackageVersion>10.0.19041.38</WindowsSdkPackageVersion>

private void button1_Click(object sender, EventArgs e) {
    System.Xml.XmlWriter w = System.Xml.XmlWriter.Create(@"c:\\temp\\booklist.xml");
 
    w.WriteStartElement("booklist");
    w.WriteAttributeString("count", "5");
 
    for (int i = 1; i <= 5; i++) {
        w.WriteStartElement("book");
        w.WriteAttributeString("isbn", (i * 10).ToString());
        w.WriteElementString("title", "book name " + i.ToString());
        w.WriteStartElement("price");
        w.WriteAttributeString("unit", "NTD");
        w.WriteString((i+500).ToString());
        w.WriteEndElement();
        w.WriteEndElement();
    }
 
    w.WriteEndElement();
 
    w.Close();
}

        // using System.Xml;

        private void button2_Click(object sender, EventArgs e) {

            XmlDocument doc = new XmlDocument();

            doc.Load(@"c:\\temp\\booklist.xml");
 
 
            (sender as Button).Text = "OK";

        }
 

    private void button2_Click(object sender, EventArgs e)
    {
        XmlDocument doc = new XmlDocument();

        string x = textBox2.Text;

        doc.Load(@"c:\\\\temp\\\\booklist.xml");

        XmlNode title = doc.SelectSingleNode($"/booklist/book[{x}]/title");
        if (title == null)
        {
            (sender as Button).Text = "not found";
            return;
        }
        textBox1.Text += title.InnerText + "\\\\r\\\\n";

        (sender as Button).Text = "OK";
    }

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