WPF TextBlock highlight certain parts based on search condition

Question

I have TextBlock that has Inlines dynamicly added to it (basically bunch of Run objects that are either italic or bold).

In my application I have search function.

I want to be able to highlight TextBlock's text that is in being searched for.

By highlighting I mean changing certain parts of TextBlock text's color (keeping in mind that it may highlight several different Run objects at a time).

I have tried this example http://blogs.microsoft.co.il/blogs/tamir/archive/2008/05/12/search-and-highlight-any-text-on-wpf-rendered-page.aspx

But it seams very unstable :(

Is there easy way to solve this problem?

Answer 1

This question is similar to How to display search results in a WPF items control with highlighted query terms

In answer to that question, I came up with an approach that uses an IValueConverter. The converter takes a text snippet, formats it into valid XAML markup, and uses a XamlReader to instantiate the markup into framework objects.

The full explanation is rather long, so I've posted it to my blog: Highlighting Query Terms in a WPF TextBlock

Answer 2

I took dthrasers answer and took out the need for an XML parser. He does a great job explaining each of the pieces in his blog, However this didn't require me to add any extra libraries, here's how I did it.

Step one, make a converter class:

class StringToXamlConverter : IValueConverter
{

    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        string input = value as string;
        if (input != null)
        {
            var textBlock = new TextBlock();
            textBlock.TextWrapping = TextWrapping.Wrap;
            string escapedXml = SecurityElement.Escape(input);

            while (escapedXml.IndexOf("|~S~|") != -1) {
            //up to |~S~| is normal
            textBlock.Inlines.Add(new Run(escapedXml.Substring(0, escapedXml.IndexOf("|~S~|"))));
            //between |~S~| and |~E~| is highlighted
            textBlock.Inlines.Add(new Run(escapedXml.Substring(escapedXml.IndexOf("|~S~|") + 5,
                                      escapedXml.IndexOf("|~E~|") - (escapedXml.IndexOf("|~S~|") + 5))) 
                                      { FontWeight = FontWeights.Bold, Background= Brushes.Yellow });
            //the rest of the string (after the |~E~|)
            escapedXml = escapedXml.Substring(escapedXml.IndexOf("|~E~|") + 5);
            }

            if (escapedXml.Length > 0)
            {
                textBlock.Inlines.Add(new Run(escapedXml));                      
            }
            return textBlock;
        }

        return null;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException("This converter cannot be used in two-way binding.");
    }

}

Step two: Instead of a TextBlock use a ContentBlock. Pass in the string (you would of used for your textBlock) to the content block, like so:

<ContentControl Margin="7,0,0,0"
                HorizontalAlignment="Left"
                VerticalAlignment="Center"
                Content="{Binding Description, Converter={StaticResource CONVERTERS_StringToXaml}, Mode=OneTime}">
</ContentControl>

Step three: Make sure the text you pass includes |~S~| before and |~E~| after the text part you want to be highlighted. For example in this string "my text |~S~|is|~E~| good" the is will be highlighted in yellow.

Notes:
You can change the style in the run to determine what and how your text is highlighted
Make sure you add your Converter class to your namespace and resources. This might also require a rebuild to get working.