Extension method for DropDownList causing error
I have an extension method for `DropDownList` that's throwing `Extension method can only be declared in non-generic, non-nested static classes` on the keyword `this`. I'm not quite sure why though since I've seen plenty of examples with extension methods on `DropDownList`

    public static class DropDownListExtensions {
        public static void populateDropDownList(this DropDownList source, Action delegateAction) {
            source.DataValueField = "Key";
            source.DataTextField = "Value";
            source.DataSource = delegateAction;
            source.DataBind();
        }
    }
Extension method for DropDownList causing error
===

I have an extension method for `DropDownList` that's throwing `Extension method can only be declared in non-generic, non-nested static classes` on the keyword `this`. I'm not quite sure why though since I've seen plenty of examples with extension methods on `DropDownList`

    public static class DropDownListExtensions {
        public static void populateDropDownList(this DropDownList source, Action delegateAction) {
            source.DataValueField = "Key";
            source.DataTextField = "Value";
            source.DataSource = delegateAction;
            source.DataBind();
        }
    }