saving data from code generated gridview template fields

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C#

i generated a gridview ,using follwing class am creating template field dynamically...when am try to read grid data its not getting value...how i can read
each row data and add to a list inorder to save to db

// data passing for generating gridview

if (dsGraphToBind.Tables[0].Rows.Count > 0)
           {
               foreach (DataColumn col in dsGraphToBind.Tables[0].Columns)
               {
                   //if (col.ColumnName != "Stage Order" && col.ColumnName != "Distance")
                   //{
                       //Declare the bound field and allocate memory for the bound field.
                       TemplateField bfield = new TemplateField();

                       //Initalize the DataField value.
                       bfield.HeaderTemplate = new GridViewTemplate(ListItemType.Header, col.ColumnName);

                       //Initialize the HeaderText field value.
                       bfield.ItemTemplate = new GridViewTemplate(ListItemType.Item, col.ColumnName);

                       //Add the newly created bound field to the GridView.
                       grvBaseFareGraph.Columns.Add(bfield);
                   }
               //}
           } 


// class used for generating gridview...
public  class GridViewTemplate : ITemplate
    {
        //A variable to hold the type of ListItemType.
        ListItemType _templateType;

        //A variable to hold the column name.
        string _columnName;

        //Constructor where we define the template type and column name.
        public GridViewTemplate(ListItemType type, string colname)
        {
            //Stores the template type.
            _templateType = type;

            //Stores the column name.
            _columnName = colname;
        }

        void ITemplate.InstantiateIn(System.Web.UI.Control container)
        {
            switch (_templateType)
            {
                case ListItemType.Header:
                    //Creates a new label control and add it to the container.
                    Label lbl = new Label();            //Allocates the new label object.
                    lbl.Text = _columnName;             //Assigns the name of the column in the lable.
                    container.Controls.Add(lbl);        //Adds the newly created label control to the container.
                    break;

                case ListItemType.Item:
                    //Creates a new text box control and add it to the container.
                    TextBox tb1 = new TextBox();                            //Allocates the new text box object.
                    tb1.DataBinding += new EventHandler(tb1_DataBinding);   //Attaches the data binding event.
                 
                    tb1.Columns = 4;                                        //Creates a column with size 4.
                    container.Controls.Add(tb1);                            //Adds the newly created textbox to the container.
                    break;

                case ListItemType.EditItem:
                    //As, I am not using any EditItem, I didnot added any code here.
                    break;

                case ListItemType.Footer:
                    CheckBox chkColumn = new CheckBox();
                    chkColumn.ID = "Chk" + _columnName;
                    container.Controls.Add(chkColumn);
                    break;
            }
        }
        /// <summary>
        /// This is the event, which will be raised when the binding happens.
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        void tb1_DataBinding(object sender, EventArgs e)
        {
            TextBox txtdata = (TextBox)sender;
            txtdata.ID = "gtx";
            GridViewRow container = (GridViewRow)txtdata.NamingContainer;
            object dataValue = DataBinder.Eval(container.DataItem, _columnName);
            if (dataValue != DBNull.Value)
            {

                txtdata.Text = dataValue.ToString();

            }
          
        }