Question

I am attempting to use a findcontrol method to dynamically fill a drop down list. I keep getting a null reference and have tried a couple different ways. Here is some code that Ive tried.

<ItemTemplate>
   <asp:DropDownList runat="server" 
           ID="ddlCalculateGrid" 
           Style="border: none; border-width: 0px; width: 90%"
           OnSelectedIndexChanged="ddlCalculateGrid_OnSelectedIndexChanged"
           AutoPostBack="true">
   </asp:DropDownList>
   <asp:HiddenField runat="server" 
           ID="hdnCalculate" 
           Value='<%# Eval("Calculate") %>' />
</ItemTemplate>

and here is the back end code.

        DropDownList tempddl;
        tempddl = (DropDownList)grvbillDetail.FindControl("ddlCalculateGrid");
        tempddl.DataSource = rcta.GetDataByTrueValue();
        tempddl.DataBind();

Answer 1

Your dropdown is in an item template. This means your gridview could contain several drop downs (one in each row) or none at all if the gridview is bound to a source with no rows.

If you’re looking to bind each dropdown for each row, you would do so in the GridViewRowDatabound event like so.

protected void Page_Load(object sender, EventArgs e)
{
    grvbillDetail.RowDataBound += grvbillDetail_RowDataBound;
}

void grvbillDetail_RowDataBound(object sender, GridViewRowEventArgs e)
{
    if (e.Row.RowType != DataControlRowType.DataRow)
        return;
    var ddl = e.Row.FindControl("ddlCalculateGrid") as DropDownList;
    if (ddl != null)
    {
        ddl.DataSource = rcta.GetDataByTrueValue();
        ddl.DataBind();
    }
}
}