how to get value of textbox from modal popupextender to textbox on the page

Hi,

I have text boxes and modalpupextender on the same page, when i click button, modalpopup show and find data in the database and show in the grid on the modal popup.

when i click the row of the grid , get the selected value and fill in the text box on the page. i done all of it. but i could not fill value into text box.

below code is which will get data frome the grid which is on the modalpopup.

            if (e.CommandName == "goback")
            {
                int supplierId = Convert.ToInt32(e.CommandArgument);
                GridViewRow row = (GridViewRow)(((Control)e.CommandSource).NamingContainer);
                LinkButton lnkbtnSupplierNameSearch = row.FindControl("lnkbtnSupplierNameSearch") as LinkButton;
                LinkButton lnkbtnUCodeSearch = row.FindControl("lnkbtnUCodeSearch") as LinkButton;
                LinkButton lnkbtnSCodeSearch = row.FindControl("lnkbtnSCodeSearch") as LinkButton;

                string supplierName = lnkbtnSupplierNameSearch.Text;
                string supplierUniqueCode = lnkbtnUCodeSearch.Text;
                string baseCurrency = lnkbtnSCodeSearch.Text;

                //TextBox txtSupplierName = (TextBox)Page.FindControl("txtSupplierName");
                ////TextBox txtSupplierCode = (TextBox)Page.FindControl("txtSupplierCode");
                ////TextBox txtSupplierCurrency = (TextBox)Page.FindControl("txtSupplierCurrency");

                txtSupplierName.Text = supplierName;       // cant fill up into the text which is on the same page
                txtSupplierCode.Text = supplierUniqueCode; // cant fill up into the text which is on the same page
                txtSupplierCurrency.Text = baseCurrency; // cant fill up into the text which is on the same page

                modalUpdate.Hide();
            }

please advice