values of the radioButton in templateField on button Click

<asp:gridview ID="gridview1"  runat="server" AutoGenerateColumns="false">
    <Columns>
        <asp:BoundField DataField="Name"  HeaderText="Name"/>
        <asp:TemplateField HeaderText="Attendance">
        <ItemTemplate >
        <asp:RadioButton ID="rb1" runat="server" Text="P"  GroupName="1" />
        <asp:RadioButton ID="RadioButton1" Text="A" runat="server"  GroupName="1"/>
        <asp:RadioButton ID="RadioButton2" Text="L" runat="server"  GroupName="1"/>
        <asp:RadioButton ID="RadioButton3" Text="H" runat="server" GroupName="1" />
        </ItemTemplate>
        </asp:TemplateField>
    </Columns>
</asp:gridview>
        <asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="Submit" />



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how i can get the value of the gridview on button click