Waiting for a text change in WatiN

Question

I am trying to test a web page that has ajax calls to update a price. An ajax call is fired on page load to update an initially empty div.

This is the extension method I'm using to wait for a change in the inner text of the div.

public static void WaitForTextChange(this IE ie, string id)
{
    string old = ie.Element(id).Text;
    ie.Element(id).WaitUntil(!Find.ByText(old));
}

However it's not pausing even though when I write out the old value and ie.Element(id).Text after the wait, they are both null. I can't debug as this acts as a pause.

Can the Find.ByText not handle nulls or have I got something wrong.

Has anyone got some code working similar to this?

Answer 1

I found my own solution in the end after delving into WatiN's constraints.

Here's the solution:

public class TextConstraint : Constraint
{
 private readonly string _text;
 private readonly bool _negate;

 public TextConstraint(string text)
 {
  _text = text;
  _negate = false;
 }

 public TextConstraint(string text, bool negate)
 {
  _text = text;
  _negate = negate;
 }

 public override void WriteDescriptionTo(TextWriter writer)
 {
  writer.Write("Find text to{0} match {1}.", _negate ? " not" : "", _text);
 }

 protected override bool MatchesImpl(IAttributeBag attributeBag, ConstraintContext context)
 {
  return (attributeBag.GetAdapter<Element>().Text == _text) ^ _negate;
 }
}

And the updated extension method:

public static void WaitForTextChange(this IE ie, Element element)
{
    string old = element.Text;
    element.WaitUntil(new TextConstraint(old, true));
}

It assumes that the old value will be read before the change so there's a slight chance of a race condition if you use it too long after setting off the update but it works for me.