Highlighting search results Leave feedback

This page describes how to highlight search results in the text of a document.

After performing a search, occurrences of found words and phrases for a particular document can be highlighted in the text of the document using the Highlight method of the Index class. To do this, a highlighter of the corresponding type must be passed as an argument to the method.

The Index class also represents an overload of the Highlight method, which takes an object of the HighlightOptions class as an argument. The HighlightOptions class contains properties for setting the following options:

• CustomExtractor is an extractor used during indexing, it is necessary if the text of the document was not saved in the index.
• AdditionalFields are additional document fields added during document indexing which are also necessary if the document text was not saved in the index.
• Cancellation is an object used to cancel the operation.
• GenerateHead is a flag to specify whether the Head tag is generated in the output HTML.
• MetadataIndexingOptions is an object for specifying metadata indexing options.
• UseInlineStyles is a flag to specify whether inline styles or CSS class are used to highlight occurrences.
• HighlightColor is a color used to highlight occurrences.
• TermHighlightStartTag is the start tag of the highlighting of the found word. This tag is used only when highlighting in plain text.
• TermHighlightEndTag is the end tag of the highlighting of the found word. This tag is used only when highlighting in plain text.

The other options are used for highlighting occurrences in text fragments.

To highlight search results in the text of the whole document, a highlighter of the DocumentHighlighter class is used. To create a highlighter of this type, you must pass an object of a class derived from the abstract class OutputAdapter to its constructor. Details on the output adapters are presented on the page Output adapters.

If after generation the text of a document was saved to a file, this file can be opened by an Internet browser to navigate the occurrences of the words found. To navigate the occurrences, the following text is added to the URL in a browser:

#hitN

where N is a number starting from zero. The full document URL in a browser might look like this:

file:///C:/Text.html#hit0

The following example demonstrates how to highlight search results in the text of an entire document.

C#

string indexFolder = @"c:\MyIndex\";
string documentFolder = @"c:\MyDocuments\";

// Creating an index settings instance
IndexSettings settings = new IndexSettings();
settings.TextStorageSettings = new TextStorageSettings(Compression.High); // Enabling storage of extracted text in the index

// Creating an index in the specified folder
Index index = new Index(indexFolder, settings);

// Indexing documents from the specified folder
index.Add(documentFolder);

// Search for the word 'Universe'
SearchResult result = index.Search("Universe");

// Highlighting occurrences in the text
if (result.DocumentCount > 0)
{
    FoundDocument document = result.GetFoundDocument(0); // Getting the first found document
    StructureOutputAdapter outputAdapter = new StructureOutputAdapter(OutputFormat.PlainText); // Creating the output adapter
    Highlighter highlighter = new DocumentHighlighter(outputAdapter); // Creating the highlighter instance
    HighlightOptions options = new HighlightOptions(); // Creating the highlight options
    options.TermHighlightStartTag = "<Term>"; // Setting the start tag for the found word
    options.TermHighlightEndTag = "</Term>"; // Setting the end tag for the found word
    index.Highlight(document, highlighter, options); // Generating plain text with highlighted occurrences

    DocumentField[] fields = outputAdapter.GetResult();
    Console.WriteLine(document.ToString());
    for (int i = 0; i < fields.Length; i++)
    {
        // Printing field names of the found document
        DocumentField field = fields[i];
        Console.WriteLine("\t" + field.Name);
    }
}

Occurrences can also be highlighted in separate HTML or plain text fragments. For this, the highlighter of the FragmentHighlighter class is used. The following properties are presented in the HighlightOptions class to use with the highlighter of this type:

• TermsBefore is used to specify the maximum number of words in a text fragment before highlighted word. The value must be in the range from 0 to 10000. The default value is 7.
• TermsAfter is used to specify the maximum number of words in a text fragment after highlighted word. The value must be in the range from 0 to 10000. The default value is 7.
• TermsTotal is used to specify the maximum number of words in a text fragment. The value must be in the range from 0 to 10000. The default value is 21.
• TermHighlightStartTag is the start tag of the highlighting of the found word. This tag is used only when highlighting in plain text.
• TermHighlightEndTag is the end tag of the highlighting of the found word. This tag is used only when highlighting in plain text.

Generated text fragments with highlighted occurrences can be used, for example, to generate web pages containing search results on a site.

The example below demonstrates how to highlight search results in separate text fragments.

C#

string indexFolder = @"c:\MyIndex\";
string documentsFolder = @"c:\MyDocuments\";

// Creating an index settings instance
IndexSettings settings = new IndexSettings();
settings.TextStorageSettings = new TextStorageSettings(Compression.High); // Enabling storage of extracted text in the index

// Creating an index in the specified folder
Index index = new Index(indexFolder, settings);

// Indexing documents from the specified folder
index.Add(documentsFolder);

// Search for the word 'Einstein'
SearchResult result = index.Search("Einstein");

// Assigning highlight options
HighlightOptions options = new HighlightOptions();
options.TermsBefore = 5;
options.TermsAfter = 5;
options.TermsTotal = 15;
options.HighlightColor = new Color(0, 0, 127);
options.UseInlineStyles = true;

// Highlighting found words in separate text fragments of a document
FoundDocument document = result.GetFoundDocument(0);
FragmentHighlighter highlighter = new FragmentHighlighter(OutputFormat.Html);
index.Highlight(document, highlighter, options);

// Getting the result
FragmentContainer[] fragmentContainers = highlighter.GetResult();
for (int i = 0; i < fragmentContainers.Length; i++)
{
    FragmentContainer container = fragmentContainers[i];
    string[] fragments = container.GetFragments();
    if (fragments.Length > 0)
    {
        Console.WriteLine(container.FieldName);
        Console.WriteLine();
        for (int j = 0; j < fragments.Length; j++)
        {
            // Printing HTML markup to console
            Console.WriteLine(fragments[j]);
            Console.WriteLine();
        }
    }
}

You may easily run the code from documentation articles and see the features in action in our GitHub examples:

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