I have read through this which helped me narrow down my validation problems to the InitialValue property of the RequiredFieldValidator.
My drop down list is a list of objects which are populated by the code behind like this;
brands.Insert(0, Brand.Empty)
cbBrand.DataValueField = "ID";
cbBrand.DataTextField = "Name";
cbBrand.DataSource = new BindingList<Brand>(brands);
cbBrand.DataBind();
where Brand.Empty is a null object type.
Where I'm coming unstuck is getting the IntialValue to accept a null value. For instance, InitialValue="" fails to recognise the empty object in the list.
Can anyone point me in the direction of a fix for this?
Wow. I thought I had searched previous answers on this site very thoroughly before posting this question, but I had missed this!!
The answer is to change your <asp:DropDownList> to have the property AppendDataBoundItems=true, Then add an <asp:ListItem Text="" Value="" /> between the dropDownList tags and BAM! you can insert a value to the list that does not require the null object inserted in the code behind (which should be removed so that you don't end up with 2 blanks at the start of your list).
The benefit here is that the list in my code-behind is bound to an object type <Brand>, but adding the empty string at the client works fine for client-side validation.
Hope this helps anyone else struggling with this problem!