Custom formatting of validation errors & control tree issues - ASP.NET

Question

Hi,

I have a WebControl library I'm using to render out our stylized form elements. The library also contains some overriden validators, so that when used together, I can render out some nicer validation HTML/CSS than the default validator's red-star-next-to-a-field. Namely, I'd like to highlight the entire line.

At its most basic level, the 'form line' could render out:

• Outer <div class="hasError">
  • <asp:Label>
  • <asp:TextBox>

(From there, there's all sorts of extra whistles, AssociatedControlID...)

The issue I'm having is that when having the control create its own overriden validator (e.g. controlled with a IsRequiredField property), I'm unable to get the validator's ControlToValidate to target the control itself.

It would seem the validator's target ControlToValidate needs to be at the same level in the control tree. And I can't add it to the Parent's control tree during CreateChildControls, as it gives an error.

... So I have a class like this:

[DefaultProperty("Value"), ValidationProperty("Value")]  
public class BasicTextInputLine : WebControl, INamingContainer  
{  
  ...
  private Label _someLabel;
  private TextBox _someTextBox;
  private MyRequiredFieldValidator _someValidator;

  public string Value  
  public bool IsRequiredField  
  ...  
}

(Note - The ValidationProperty("Value") flag allows a validator to point at it)

and

public class MyRequiredFieldValidator : RequiredFieldValidator
{
  ...
  protected override void OnPreRender(EventArgs e)
  {
    ...
    if (foundControlToValidate is BasicTextInputLine)
      (foundControlToValidate as BaseFormEntry).IsValid = false;
}

Which I can happily works in markup like so:

<custom:BasicTextInputLine ID="foo" ... />
<custom:MyRequiredFieldValidator ControlToValidate="foo" ... />

Issue:
Unfortunately, I have a catch-22 when adding things to the control tree:

Adding it to the parent (which would give a working control tree) gives an error about not being able to interfere with its control set.

protected override void CreateChildControls()
{
  ...
  Parent.Controls.Add(_someValidator);
}

And adding it to the control gives an error about the ControlToValidate not being able to be found.

protected override void CreateChildControls()
{
  ...
  Controls.Add(_someValidator);
}

How can I structure this so I can have BasicTextInputLine create its own validator, and have it validate itself, not its inner TextBox?

Much appreciated.