Inherited Textbox required validator

[bcutting]

I have a control which inherits from TextBox and supplies some
additional data functionality. I was hoping to include a boolean flag
"Required" that can be set in the designer. When the flag is set to
True the control should include a RequiredFieldVa lidator for itself.
No matter how I add the validator within the control it never seems to
show up in the page.

protected override void CreateChildCont rols()
{
if(m_bRequiredF ield)
{
RequiredFieldVa lidator rfv = new RequiredFieldVa lidator ();
rfv.ControlToVa lidate = this.ID;
rfv.Display = ValidatorDispla y.Dynamic;
rfv.ErrorMessag e = UserFieldName + " is required.";
this.Controls.A dd(rfv);
}
base.CreateChil dControls ();
}
I would like to avoid creating a composite control. I have also tried
other events such as PreRender and DataBind.

I even tried hacking the text HTML for the validator in the Render and
add an empty validator to the Page.Validators with the same clientID.
But the page doesn't seem to register it.

my attempted hack

protected override void OnPreRender(Eve ntArgs e)
{
RequiredFieldVa lidator rvf = new RequiredFieldVa lidator ();
rvf.ID=this.Cli entID + "_Validator ";
Page.Validators .Add(rvf);
base.OnPreRende r (e);
}
protected override void Render(HtmlText Writer writer)
{
base.Render (writer);
if(m_bRequiredF ield)
{
writer.Write("< span id=\""+this.Cli entID+"_Validat or\" " +
"controltovalid ate=\"" + this.ClientID + "\" " +
"errormessage=\ ""+UserFieldNam e+" is required\" display=\"Dynam ic\"
evaluationfunct ion=\"RequiredF ieldValidatorEv aluateIsValid\" " +
"initialvalue=\ "\" style=\"color:R ed;display:none ;\">*</span>");
}
}
Any ideas would be appreciated.