Measure length of text for a label

I'm trying to dynamically shorten a label based on available space. I use FormattedText to determine the length of the 开发者_开发技巧candidate string

formattedText = new FormattedText(candidateString, CultureInfo.CurrentCulture, FlowDirection.LeftToRight, typeface, FontSize = fontSize, Brushes.Black);

I should be able to retrieve the Typeface from the Label containing the text; however I keep running into roadblocks:

• Label contains FontFamily but not Typeface.
• I can't create a new Typeface from FontFamily since I can't get a single FontFamily name

  Typeface t = new Typeface(theLabel.FontFamily.FamilyNames.?, theLabel.FontStyle, theLabel.FontSize, theLabel.FontStretch);

This seems like it ought to be simple: I want the typeface used in THAT label (pointing to screen). How can a create a Typeface for use in measuring my string length? Is there a simpler way to accomplish this? What am I missing here?

Thanks.

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This doesn't work?

Typeface t = new Typeface(theLabel.FontFamily,theLabel.FontStyle,theLabel.FontWeight,theLabel.FontStretch, new FontFamily("Arial"));

or you can experiment with

theLabel.FontFamily.GetTypefaces();