Textbox value cannot get from gridview. within submit button

Question

I cannot get text box value within submit button.. I got null value.. Anyone help me..

protected void btnSubmit_Click(object sender, EventArgs e)

    {

        foreach (GridViewRow gridRow in GridView1.Rows)

        {

TextBox serviceFee = (TextBox)gridRow.FindControl("txtServiceFee");

            TextBox typingFee = (TextBox)gridRow.FindControl("txtTypingFee");

            TextBox govermentFee = (TextBox)gridRow.FindControl("txtGovermentFee");

            int customerTypeId = Convert.ToInt32(lbl.Text);

            string sfee = Convert.ToString(serviceFee.Text);

            Response.Write("sFee:"+sfee);
}
}