DataAdapter.Update not working

Can anybody help me on this.
I am just having a simple table testxmlmsg with 4 fields, serno, timestamp, bytexmlmsg, userid.
The serno is set as primary.

I am trying to update the data using the bellow function. No error or exception is coming but the data are not getting updated in the database.
Note that I do not want to use the QueryBuilder.

Thanks in advance for any help.

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 Private Sub updateRecord()
    Dim connection As IfxConnection
    Dim Transaction As IDbTransaction
    Dim DataAdapter As IfxDataAdapter = New IfxDataAdapter
    Dim UpdateCommand As IfxCommand
    Dim SelectCommand As IfxCommand


    Try
      connection = New IfxConnection(txtConnection.Text)
      connection.Open()

      Try
        Transaction = connection.BeginTransaction()

        Try
          Dim data As DataSet = New DataSet

          UpdateCommand = connection.CreateCommand
          SelectCommand = connection.CreateCommand

          SelectCommand.CommandText = "SELECT userid FROM testxmlmsg"
          SelectCommand.Transaction = Transaction
          SelectCommand.Connection = connection

          DataAdapter.SelectCommand = SelectCommand


          UpdateCommand.Transaction = Transaction
          UpdateCommand.Connection = connection
          UpdateCommand.CommandText = "UPDATE testxmlmsg SET userid = 2"
          DataAdapter.UpdateCommand = UpdateCommand
     
          DataAdapter.Fill(data)

         Dim cRow As DataRow 

          For Each cRow In data.Tables(0).Rows
            cRow(0) = 2
          Next
  
           DataAdapter.Update(data)

          data.AcceptChanges()
        Catch exc As Exception
          txtUpdateError.Text = exc.Message
        End Try
      Catch exc As Exception
        txtUpdateError.Text = exc.Message
      Finally
        connection.Close()
      End Try
    Catch exc As Exception
      txtUpdateError.Text = exc.Message
    Finally
      connection.Dispose()
    End Try

  End Sub