C#

namespace XML_Dataset
{
    public partial class Form1 : Form
    {
        private searchTable testSearchTable = new searchTable();

        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            this.dataGridView1.DataSource = this.testSearchTable.Tables["search"];
        }

        private void getDataFromAS_Click(object sender, EventArgs e)
        {
            this.testSearchTable.Clear();
            this.testSearchTable.ReadXml(this.testXMLStringAddr.Text);
        }

        private void generateDatasetToFile_Click(object sender, EventArgs e)
        {
            System.IO.StreamWriter xmlSW = new System.IO.StreamWriter("testSearchTable.xml");
            this.testSearchTable.WriteXml(xmlSW, XmlWriteMode.WriteSchema);
            xmlSW.Close();
            MessageBox.Show("XML Schema was generatoted to the file: testSearchTable.xml");
        }
    }
}

using (FileStream fs = new FileStream("Log.txt", FileMode.Append, FileAccess.Write, FileShare.None) {
    StreamWriter sw = new StreamWriter(fs);
    sw.WriteLine(...);
    sw.Close();
}