If you are like me, you hate having to create the required field validators for a bunch of TextBox controls.  Even more if you are adding Ajax ValidatorCallout controls to all of them.  Sure, you could create another server control to extent the Textbox to automatically include this…but here is a simple alternative.

I created a method that cycles through all of the controls and checks to see if it has the attribute “Required”, and if so, then add the RequiredFieldValidator and Ajax callout controls automatically. You could obviously expand on this to meet your specific needs.
Here is how you would markup your TextBox control:
<asp:TextBox Required=”true” ValidationGroup=”valGroup” ID=”TextBox1″ runat=”server” />

Here is the method in the code behind:

private void AddRequiredValidations(ControlCollection controls)
{
    List requiredValidators = new List();
    for (int i = 0; i < controls.Count; i++)
    {
        if (controls[i] is TextBox)
        {
            TextBox tb = (TextBox)controls[i];
            if (tb.Attributes["Required"] != null && Convert.ToBoolean(tb.Attributes["Required"]))
            {
                RequiredFieldValidator requiredValidator = new RequiredFieldValidator();
                requiredValidator.ErrorMessage = "Required";
                requiredValidator.ID = "required" + tb.ID;
                requiredValidator.Display = ValidatorDisplay.None;
                requiredValidator.ValidationGroup = tb.ValidationGroup;
                requiredValidator.ControlToValidate = tb.ID;
                // Add the RequiredFieldValidator to a list to be added later
                // Since we can't add them to the control as we are cycling through them
                requiredValidators.Add(requiredValidator); 

                tb.CausesValidation = true;
            }
        }

        if (controls[i].HasControls()) // If this control has child controls
        {
            AddRequiredValidations(controls[i].Controls); // Search the child controls too
        }
    }

    // Now we can actually add the RequiredFieldValidators since we are done cycling through the existing controls
    for (int i = 0; i < requiredValidators.Count; i++)
    {

        AjaxControlToolkit.ValidatorCalloutExtender callout = new AjaxControlToolkit.ValidatorCalloutExtender();
        callout.TargetControlID = requiredValidators[i].ID;
        callout.ID = requiredValidators[i].ID + "Callout";
        controls.Add(requiredValidators[i]);
        controls.Add(callout);
    }
}

Then all you have to do is call it in your Page_Load() method:

AddRequiredValidations(this.Controls);

This will work not only for a singe TextBox control, but also for TextBox controls buried inside a GridView or Repeater!