ClassificationSample

title	Classification Extension Sample reference
description	A reference for Classification sample
date	2025-04-22

Classification Extension Sample

This extension creates a tagger that classifies the text of CSV files.

A detailed walkthrough of how to create a tagger is available in the Taggers sample readme file. Please read that first.

This sample's CsvTaggerProvider and CsvTagger are equivalent to MarkdownTextMarkerTaggerProvider and MarkdownTextMarkerTagger.

Classification

Classification can be performed by an extension by implementing an ITextViewTaggerProvider<ClassificationTag> and have the TextViewTagger<> generate ClassificationTag values.

tags.Add(
    new TaggedTrackingTextRange<ClassificationTag>(
        new TrackingTextRange(
            document,
            tagStartPosition,
            tagLength,
            TextRangeTrackingMode.ExtendNone),
        new ClassificationTag(ClassificationType.KnownValues.Operator)));

At this time, VisualStudio.Extensibility doesn't support defining text colors for new classification types yet, so we must use existing classification types.

VSSDK-compatible extensions, can use ClassificationTypeDefinition to define new classification types. Their name can be referenced using ClassificationType.Custom.

Performance considerations

Since CsvTagger doesn't support CSV fields containing line breaks, the tagger can perform parsing of any single line of the CSV file independently from each other. This allows the tagger to only act on the modified lines.

We further optimize the tag generation by intersecting the edited text ranges with the ranges that have been previously requested (GetAllRequestedRangesAsync). This is particularly useful if the user pastes a large amount of text into the file resulting in lines being edited that don't fall into the currently visible portion of the view.

If these optimization were not possible, we would have to avoid generating tags on each edit of the document (see the Implementing "slow" taggers chapter of the Taggers sample readme file).