<asp:GridView ID="GridView1" runat="server" OnRowDataBound="GridView1_RowDataBound">
<Columns>
<asp:TemplateField HeaderText="TextBox">
<ItemTemplate>
<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
</ItemTemplate>
</asp:TemplateField>
aspx.cs file:
protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
{
if ( e.Row.RowType == DataControlRowType.DataRow )
{
TextBox textBox1 = (TextBox)e.Row.FindControl("TextBox1");
}
}