ASP.net loop through GridView and gather Template column textbox values and tooltip

Hi

I have an ASP.net Gridview that contains Template TextBox columns
I want to loop through and check the text box text and tooltip text
How do I do this in the following code? The sort of template columns are shown
below

            For i As Integer = 0 To Me.GridView1.Columns.Count - 1
                oColIndex = i + 2
                For r As Integer = 0 To Me.GridView1.Rows.Count - 1
                           'I need to gather the text box value and tooltip here
                Next r
            Next i

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     <asp:TemplateField HeaderText="D1" Visible="false" ItemStyle-Wrap="true" >
                           <ItemTemplate>
                                <asp:Textbox ID="D1" runat="server"  Visible="true" Width="20"></asp:Textbox>
                           </ItemTemplate>
                      </asp:TemplateField>
                      <asp:TemplateField HeaderText="D2" Visible="false" ItemStyle-Wrap="true" >
                           <ItemTemplate>
                                <asp:Textbox ID="D2" runat="server"  Visible="true" Width="20" ></asp:Textbox>
                           </ItemTemplate>
                      </asp:TemplateField>
                     <asp:TemplateField HeaderText="D3" Visible="false" ItemStyle-Wrap="true">
                           <ItemTemplate>
                                <asp:Textbox ID="D3" runat="server"  Visible="true" Width="20" ></asp:Textbox>
                           </ItemTemplate>

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