How can i get HellselectedItemValue from Dropdownlist in Gridview?

Hello,

I have a new problem and after two days searching i still find no solution.

In my Gridview ItemTemplate i have a dropdownlist and a button.
After button-click i use the selectedItemValue of the dropdownlist to change my wizard1.ActiveStepIndex and the value of buttons commandargument.

<itemTemplate>
 <asp:DropDownList ID="ddAuswahl"
       DataTextField="navText"
        DataValueField = "id" DataSource= '<%# PopulateControls() %>' runat="server">
   </asp:DropDownList>

        <asp:ImageButton ID="btnAuswahl"
       CommandArgument='<%# ...