1:
2:
3:
4:
5:
6:
7:
8:
9:
10:
11:
12:
13:
14:
15:
16:
17:
18:
19:
20:
21:
22:
23:
24:
25:
26:
27:
28:
29:
30:
31:
32:

        DataSet DataSet { get; set; }

        const string _xmlPath = "data.xml";

        public MainForm()
        {
            DataSet = new DataSet();
            InitializeComponent();

            if (File.Exists(_xmlPath))
                DataSet.ReadXml(_xmlPath);
            else
                CreateTable();

            dataGridView1.DataSource = DataSet.Tables["data"];

        }

        private void CreateTable()
        {
            DataTable dataTable = new DataTable("data");
            dataTable.Columns.Add("url", typeof(Uri));
            dataTable.Columns.Add("username", typeof(string));
            dataTable.Columns.Add("password", typeof(string));

            DataSet.Tables.Add(dataTable);
        }

        private void MainFormClosing(object sender, FormClosingEventArgs e)
        {            
            DataSet.WriteXml(_xmlPath,XmlWriteMode.WriteSchema);
        }