Getting selected index and row of drop down menu inside grid view

Question

I have a gridview in which a cell is populated with a drop down list if certain conditions are met:

protected void viewThemeTypeAssociationsGridView_OnRowDataBound(Object sender, GridViewRowEventArgs e)
{
    if (e.Row.Cells[1].Text == " ")
    {
        if (e.Row.RowType == DataControlRowType.DataRow)
        {
            e.Row.Cells[1].Text = "Not Assigned";
            DropDownList chooseThemeTypeDropDown = (DropDownList)e.Row.FindControl("chooseThemeTypeDropDown");
            chooseThemeTypeDropDown.Visible = true;
        }
    }
}

Here is a picture:

This is many copies of a drop down list what is made visible in certain rows. How do get access to the selected index for the changed dropdown list and which row it is on?

I was thinking something like this but it doesn't work:

protected void chooseThemeTypeDropDown_OnSelectedIndexChanged(object sender, EventArgs e)
{
    DropDownList chooseThemeTypeDropDown = (DropDownList)e.Row.FindControl("chooseThemeTypeDropDown");
}

EDIT: If it helps here is the gridview:

                        <asp:GridView ID="viewThemeTypeAssociationsGridView" runat="server" AutoGenerateColumns="False"
                            BackColor="#DEBA84" BorderColor="#DEBA84" BorderStyle="None" BorderWidth="1px"
                            CellPadding="3" CellSpacing="2" DataSourceID="SqlDataSource6" OnRowDataBound="viewThemeTypeAssociationsGridView_OnRowDataBound">
                            <Columns>
                                <asp:BoundField DataField="Name" HeaderText="Name" SortExpression="Name" />
                                <asp:BoundField DataField="Type" HeaderText="Type" SortExpression="Type" />
                                <asp:TemplateField HeaderText="Choose Theme Type">
                                    <ItemTemplate>
                                        <asp:DropDownList ID="chooseThemeTypeDropDown" runat="server" DataTextField="Type" DataValueField="PK_ThemeType" AutoPostBack="true" DataSourceID="SqlDataSource9" CssClass="dropDownList" OnDataBound="chooseThemeTypeDropDown_OnDataBound" Visible="false" OnSelectedIndexChanged="viewProductAssociationsDropDown_OnSelectedIndexChanged">
                                        </asp:DropDownList>
                                        <asp:SqlDataSource ID="SqlDataSource9" runat="server" ConnectionString="<%$ ConnectionStrings:ApplicationServices %>"
                                            SelectCommand="SELECT [Type], [PK_ThemeType] FROM [ThemeType] WHERE [Deleted] = 0 ORDER BY [Type] ASC">
                                        </asp:SqlDataSource>
                                    </ItemTemplate>
                                </asp:TemplateField>
                            </Columns>
                            <FooterStyle BackColor="#F7DFB5" ForeColor="#8C4510" />
                            <HeaderStyle BackColor="#A55129" Font-Bold="True" ForeColor="White" />
                            <PagerStyle ForeColor="#8C4510" HorizontalAlign="Center" />
                            <RowStyle BackColor="#FFF7E7" ForeColor="#8C4510" />
                            <SelectedRowStyle BackColor="#738A9C" Font-Bold="True" ForeColor="White" />
                            <SortedAscendingCellStyle BackColor="#FFF1D4" />
                            <SortedAscendingHeaderStyle BackColor="#B95C30" />
                            <SortedDescendingCellStyle BackColor="#F1E5CE" />
                            <SortedDescendingHeaderStyle BackColor="#93451F" />
                        </asp:GridView>
                        <asp:SqlDataSource ID="SqlDataSource6" runat="server" ConnectionString="<%$ ConnectionStrings:ApplicationServices %>"
                            SelectCommand="SELECT [Theme].[Name], [ThemeType].[Type] FROM [Theme] LEFT OUTER JOIN [ThemeType] ON [Theme].[ThemeTypeId] = [ThemeType].[PK_ThemeType] JOIN [ProductTheme] ON [ProductTheme].[ThemeId]=[Theme].[PK_Theme] WHERE ProductTheme.ProductID LIKE @productParam AND ProductTheme.ThemeId = Theme.PK_Theme AND COALESCE([THEME].[THEMETYPEID], 'null') LIKE @assignedParam GROUP BY [Theme].[Name], [ThemeType].[Type] ORDER BY CASE WHEN [ThemeType].[Type] IS NULL THEN 0 ELSE 1 END, [Theme].[Name]">
                            <SelectParameters>
                                <asp:QueryStringParameter Name="productParam" Type="String" />
                                <asp:QueryStringParameter Name="assignedParam" Type="String" />
                            </SelectParameters>
                        </asp:SqlDataSource>

EDIT 2: Current code

protected void chooseThemeTypeDropDown_OnSelectedIndexChanged(object sender, EventArgs e)
{
    DropDownList chooseThemeTypeDropDown = sender as DropDownList;
    if (chooseThemeTypeDropDown != null)
    {
        System.Diagnostics.Debug.WriteLine(chooseThemeTypeDropDown.SelectedItem.Value.ToString());
    }
}

Answer 1

You really need to move the if (e.Row.RowType == DataControlRowType.DataRow) to the outside of your conditional in OnRowDataBound.

Now, if you set chooseThemeTypeDropDown.AutoPostBack to true, and set it to handle the OnSelectedIndexChanged event, you'll be able to find the correct instance of chooseThemeTypeDropDown by casting object sender as a DropDownList.

To get the row index, that is more difficult. The quickest, but kinda hacky way, is to append the rowindex to each chooseThemeTypeDropDown ID on the GridView's RowDataBound event.

chooseThemeTypeDropDown.ID = chooseThemeTypeDropDown.ID + e.Row.RowIndex;

Answer 2

The sender will give you the control that initiated the event, like this:

protected void chooseThemeTypeDropDown_OnSelectedIndexChanged(object sender, EventArgs e)
{
    DropDownList chooseThemeTypeDropDown = sender as DropDownList;

    // Check to make sure the drop down exists before we try to work with it
    if(chooseThemeTypeDropDown != null)
    {
        // Put logic here to work with drop down list
    }
}