How to sort the xml in datatable?

Instead of sorting the rows in the DGV itself, what I'd suggest you do is to create a DataView from your DataTable, sort the DataView by the ID column in descending order and then bind your DGV to that.

You can then convert the sorted DataView back to a new DataTable and call its WriteXml method to save it back to the file.

The code to do all this will be something like this:

   Private DV As DataView = Nothing

   Private Sub frmTesting_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

        Dim DS As New DataSet

        DS.ReadXml(Application.StartupPath & "\user.xml")

     

        If DS.Tables(0).Rows.Count = 0 Then

            MsgBox("nothing")

        Else

            DV As DataView = DS.Tables(0).DefaultView

            DV.Sort = "ID DESC"

            dtgUser.DataSource = DV         

        End If 

  

   End Sub

   Private Sub btnAdd_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAdd.Click

           

       If DV IsNot Nothing Then
           DV.ToTable().WriteXml(Application.StartupPath & "\user.xml")
       End If

            

   End Sub