Highlighting letters in TextBlock in Windows Phone 8.1 and Windows 8.1

In my current project I had to implement an interesting feature for both Windows Phone 8.1 and Windows 8.1 project of the Universal app. The idea is simply. The users want to search for a movie. They enter a search term into a TextBox and a list of results is shown. The results should have the search term highlighted in them.

The standard TextBlock used to display the movie titles does not support any kind of letter highlighting, so I had to write a custom one. I created a custom UserControl. The UserControl contains a few dependency properties Text, HighlightedText, HighlightBrush and a TextBlock. When Text or HighlightedText change, the Text is then split into multiple Runs that are added to the TextBlock.

private void Update()
{
    if (string.IsNullOrEmpty(Text) || string.IsNullOrEmpty(HighlightedText))
    {
        TB.Inlines.Clear();
        return;
    }

    TB.Inlines.Clear();
    var parts = Regex.Split(Text, HighlightedText, RegexOptions.IgnoreCase);
    var len = 0;
    foreach (var part in parts)
    {
        len = len + part.Length + 1;

        TB.Inlines.Add(new Run
        {
            Text = part
        });

        if (Text.Length >= len)
        {
            var highlight = Text.Substring(len - 1, HighlightedText.Length); //to match the case

            TB.Inlines.Add(new Run
            {
                Text = highlight,
                Foreground = HighlightBrush
            });
        }
    }
}

The whole working custom control is available at Github: https://github.com/igorkulman/Kulman.WPA81.HighlightTextBox.