Gridview - Writing grid changes from dataset to XML

[kageyone]

I am having trouble updating a dataset representation of an xml file. The xml file is read into a dataset which is bound to a gridview control. The edit functionality was added to the code and handles the edit button fine. The data is changed on one of the fields in edit mode and captured in a variable when the update button is clicked. I attempt to assign the new value to the dataset's field in the edited datarow. I have seen examples of just that. The dataset is not updated and therefore when I do the ds.WriteXml it doesn't update the xml file.

The update method:
protected void dg1_RowUpdating(Object sender, GridViewUpdateEventArgs e)
{
// Get the new values from the GridView controls
int i = dg1.Rows[e.RowIndex].DataItemIndex;

TextBox txtName = dg1.Rows[e.RowIndex].Cells[2].FindControl("txtName") as TextBox;
string strName = txtName.Text;

dg1.EditIndex = -1;
Bind_Grid(dg1, dsMon, "dsMon", "monitor");

// Update the XML file using the new values
DataSet oDs = (DataSet)dg1.DataSource;
////Response.Write("Changed Data b4 = " + oDs.Tables[0].Rows[i].ItemArray[1]);
oDs.Tables[0].Rows[i].ItemArray[1] = strName;
////Response.Write("Changed Data after = " + oDs.Tables[0].Rows[i].ItemArray[1]);

String monitorsPath = Server.MapPath("App_Data/Monitors.xml");
oDs.WriteXml(Server.MapPath("App_Data/Monitors.xml"), XmlWriteMode.IgnoreSchema);
Cache["dsMon"] = oDs;

Bind_Grid(dg1, dsMon, "dsMon", "monitor");
}

What can I do to get that field updated with the edited txtName.Text from the grid?

Thanks for any and all help.