TabIndex in Asp.net

Question

how to set tabindex in using this type of control nd inside this control have 1 gridview. <att:Attachment ID="ucAttachments" runat="server" /> my coding is page asp.cs -.  Button button1 = ucAttachments.FindControl("btnAdd") as Button;

                

                if (button1 != null)

                {

                    button1.TabIndex = 65;

                    

                } this work is proper but inside this button 1 gridview how to set tab or focus on textbox after this btnadd button.