C# : Database monitoring system using XML file

[STAThread]
        static void Main()
        {
             Application.Run(new EmployeeDatabase());
        }







//Load the XML file into Text box on Form loading event
         private void Form1_Load(object sender, EventArgs e)
        {
            if (e == null) throw new ArgumentNullException("e");
            try
            {
                DataSet ds = new DataSet();
                 ds.ReadXml(@"..\..\company.xml");
                dataGrid1.DataSource = ds.Tables[0];
                XmlDataDocument xd = new XmlDataDocument(ds);               
                 if (xd.InnerXml != null) TextBox1.Text = xd.InnerXml;
             }
             catch (XmlException ex)
             {
                 MessageBox.Show(ex.Message);
             }
         }


//Save the modified XML file when user sclicks Save button
         private void button2_Click(object sender, EventArgs e)
        {
            if (e == null) throw new ArgumentNullException("e");
            try
            {
                XmlTextReader xr = new XmlTextReader(
                     new StringReader(TextBox1.Text));
                DataSet ds = new DataSet();
                ds.ReadXml(xr);
                XmlDataDocument xd = new XmlDataDocument(ds);
                 ds.WriteXml(@"..\..\company.xml");
                dataGrid1.DataSource = xd.DataSet.Tables[0];
             }
             catch (XmlException ex)
             {
                 MessageBox.Show(ex.Message);
             }
         }



//Allow only one radio button to be selected for searching based on Emp_ID
//or Emp_Name
        private void radioButton1_CheckedChanged(object sender, EventArgs e)
        {
            if (e == null) throw new ArgumentNullException("e");
            TextBox2.ReadOnly = false;
            TextBox3.ReadOnly = true;
            TextBox2.Focus();
        }

         private void radioButton2_CheckedChanged(object sender, EventArgs e)
        {
            if (e == null) throw new ArgumentNullException("e");
            TextBox2.ReadOnly = true;
            TextBox3.ReadOnly = false;
            TextBox3.Focus();
        }

         // When user select any of radio button and clicks search button then search the
//XML file for required data and display
        private void button1_Click(object sender, EventArgs e)
        {
            DataSet ds = new DataSet();
             ds.ReadXml(@"..\..\company.xml");
            dataGrid1.DataSource = ds.Tables[0];
            XmlDataDocument xd = new XmlDataDocument(ds);
             
             if(button1.Text.Equals("Search"))
            {
                 if (radioButton1.Checked)
                {
                    XPathNavigator xn = xd.CreateNavigator();
                    XPathExpression expr = null;
                     try
                     {
                          if (xn != null)
                            expr = xn.Compile(
                                  "descendant::employees[id="+
                                TextBox2.Text + "]");
                         if (xn != null)
                        {
                            XPathNodeIterator iterator = xn.Select(expr);
                              if(xn.Select(expr).Count == 0)
                              {
                                   MessageBox.Show("Enter a valid employee Id number");
                                TextBox2.Text ="";
                                TextBox3.Text ="";
                                  TextBox4.Text="";
                                button1.Text ="Search";
                                groupBox1.Text = "Enter Search";
                                  TextBox2.Focus();
                                   return;
                            }
                            iterator.MoveNext();
                            XPathNavigator nav2 = iterator.Current.Clone();
                            nav2.MoveToFirstChild();
                            TextBox2.Text = nav2.Value;
                            nav2.MoveToNext();
                            TextBox3.Text = nav2.Value;
                            nav2.MoveToNext();
                            TextBox4.Text = nav2.Value;
                          }
                     }                      
                     catch (Exception ex)
                     {
                          MessageBox.Show(ex.Message);
                     }
                 }
                  else if (radioButton2.Checked)
                {
                    XPathNavigator xn = xd.CreateNavigator();
                    XPathExpression expr = null;
                     try
                     {
                          if (xn != null)
                            expr = xn.Compile(
                                  "descendant::employees[name='" +
                                TextBox3.Text + "']");
                        XPathNodeIterator iterator = null;
                         if (xn != null)
                        {
                            iterator = xn.Select(expr);
                              if(xn.Select(expr).Count == 0)
                              {
                                   MessageBox.Show("Enter a valid employee name(case sensitive).");
                                TextBox2.Text ="";
                                TextBox3.Text ="";
                                  TextBox4.Text="";
                                button1.Text ="Search";
                                groupBox1.Text = "Searching String:";
                                  TextBox3.Focus();
                                   return;
                              }
                          }
                          if (iterator != null)
                        {
                            iterator.MoveNext();
                            XPathNavigator nav2 = iterator.Current.Clone();
                            nav2.MoveToFirstChild();
                            TextBox2.Text = nav2.Value;
                            nav2.MoveToNext();
                            TextBox3.Text = nav2.Value;
                            nav2.MoveToNext();
                            TextBox4.Text = nav2.Value;
                          }

                     }
                      catch (XPathException exp)
                     {
                          MessageBox.Show(exp.Message);
                     }
                      catch (Exception ex)
                    {
                        MessageBox.Show(ex.Message);
                    }
                }    
                button1.Text = "Complete";
                groupBox1.Text = "Done";
            }         
             else
            {
                TextBox2.Text ="";
                TextBox3.Text ="";
                 TextBox4.Text="";
                button1.Text ="Search";
                groupBox1.Text = "Search String:";
            }
        }



//When user modifies the textbos XML content then synchronize the changed XML in
//DataGrid
        private void dataGrid1_CurrentCellChanged(object sender, EventArgs e)
        {
            if (e == null) throw new ArgumentNullException("e");
            //This function syncronize the data in datagrid and XML
            DataSet ds = new DataSet();
             ds.ReadXml(@"..\..\company.xml");
            dataGrid1.DataSource = ds.Tables[0];
            XmlDataDocument xd = new XmlDataDocument(ds);
            TextBox1.Text = xd.InnerXml;
        }

        private void button3_Click(object sender, EventArgs e)
        {
            Application.Exit();
        }
    }