I want to get the selected rowindex from the gridview. In the gridview there are 5 columns ID, name, model, code and amount. It also contains an image, which when clicked opens a popup window by which I can assign values in ID,name,model and code. Problem is that I can't assign proper values in each rows after clicking image and selecting the row in popup window.
For that I need to get the selected index where the image is clicked.

Here is the gridview Code.

<asp:GridView ID=grvSalesDetails runat=server AutoGenerateColumns=False CellPadding=4

    CssClass=mGrid ForeColor=#333333 GridLines=None OnRowDeleting=grvSalesDetails_RowDeleting

    ShowFooter=True Style=text-align: left Width=100% SelectedRowStyle=myselection>

    <Columns>

        <asp:BoundField DataField=RowNumber HeaderText=SNo />

        <asp:TemplateField HeaderText=Machine ID>

            <ItemTemplate>

                <asp:TextBox ID=txtMID runat=server Width=30px></asp:TextBox>

                <img class=style1 alt= src=../Inventory/Images/BrowseIcon.jpg onclick=SelectMachineCode(this)

                    id=imgMachine />

            </ItemTemplate>

        </asp:TemplateField>

        <asp:TemplateField HeaderText=Name>

            <ItemTemplate>

                <asp:TextBox ID=txtMName runat=server Width=120px></asp:TextBox>

            </ItemTemplate>

        </asp:TemplateField>

        <asp:TemplateField HeaderText=Model>

            <ItemTemplate>

                <asp:TextBox ID=txtMModel runat=server Width=80px></asp:TextBox>

            </ItemTemplate>

        </asp:TemplateField>

        <asp:TemplateField HeaderText=Code>

            <ItemTemplate>

                <asp:TextBox ID=txtMCode runat=server Width=70px></asp:TextBox>

            </ItemTemplate>

        </asp:TemplateField>

        <asp:TemplateField HeaderText=Amount>

            <ItemTemplate>

                <asp:TextBox ID=txtMAmount runat=server Width=90px></asp:TextBox>

            </ItemTemplate>

            <FooterStyle HorizontalAlign=Right />

            <FooterTemplate>

                <asp:Button ID=AddNewRow runat=server CssClass=btnSearch OnClick=AddNewRow_Click

                    Text=Add New Row />

            </FooterTemplate>

        </asp:TemplateField>

        <asp:CommandField ShowDeleteButton=True />

    </Columns>

    <FooterStyle BackColor=#102040 CssClass=mGrid Font-Bold=True ForeColor=White />

    <RowStyle BackColor=#EFF3FB />

    <EditRowStyle BackColor=#2461BF />

    <SelectedRowStyle BackColor=#D1DDF1 Font-Bold=True ForeColor=#333333 />

    <PagerStyle BackColor=#2461BF ForeColor=White HorizontalAlign=Center />

    <HeaderStyle BackColor=#507CD1 Font-Bold=True ForeColor=White />

    <AlternatingRowStyle BackColor=White />

</asp:GridView>

and this is the javascript

<script type=text/javascript>

var popup;

function SelectMachineCode() {

    var grvSalesDetails = document.getElementById('<%=grvSalesDetails.ClientID%>');

    popup = window.open(machine_lookup.aspx, Popup, width=600,height=300);

    popup.focus();

}



function OpenMachineLookUp() {

    var _PageUrl = machine_lookup.aspx;

    OpenNewWindow(_PageUrl, Machine Information, 800, 500);

}



function LookUpMachineValues(ID, Name, Model, Code, Usage, Description) {

    var grvSalesDetails = document.getElementById('<%=grvSalesDetails.ClientID%>');            

    var rowId=;//selected rowindex here            



        var MID = grvSalesDetails.rows[rowId].cells[1].children[0];

        MID.value = ID;

        var MName = grvSalesDetails.rows[rowId].cells[2].children[0];

        MName.value = Name;

        var MModel = grvSalesDetails.rows[rowId].cells[3].children[0];

        MModel.value = Model;

        var MCode = grvSalesDetails.rows[rowId].cells[4].children[0];

        MCode.value = Code;           

}

I've tried using hiddenfields, parentnode, childnode but couldn't get the selected rowindex.