private int StringLen(string candidate)
{
    var formattedText = new FormattedText(
        candidate,
        CultureInfo.CurrentUICulture,
        FlowDirection.LeftToRight,
        new Typeface(this.textBlock.FontFamily, this.textBlock.FontStyle, this.textBlock.FontWeight, this.textBlock.FontStretch),
        this.textBlock.FontSize,
        Brushes.Black);

    return formattedText.Width;
}