How to validate an ajax combobox with empty text?

How sh开发者_运维知识库ould I validate if my AJAX ComboBox contains text? I have tried with the ASP.NET RequiredFieldValidator but it dosen't work.

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If found a solution here: http://ajaxcontroltoolkit.codeplex.com/workitem/24417

Had to add javascript to change the controltovalidate property for the internal textbox.

string script = string.Format(@"if({0}) {0}.controltovalidate = ""{1}_TextBox"";", this.reqValidator.ClientID, this.ddlCombo.ClientID);

ScriptManager.RegisterStartupScript(this, this.GetType(), string.Format("validator trick for {0}", this.ClientID), script, true);