Extending Visual Studio editor with a new margin

Text view margins are placed into a margin container (see ContainerMarginPlacement.KnownValues) and ordered before or after relatively to other margins (see MarginPlacement.KnownValues).

Text view margin providers implement ITextViewMarginProvider interface, configure the margin they provide by implementing TextViewMarginProviderConfiguration and when activated, provide UI control to be hosted in the margin via CreateVisualElementAsync.

Because extensions in VisualStudio.Extensibility might be out-of-process from the Visual Studio, we can't directly use WPF as a presentation layer for content of text view margins. Instead, providing a content to a text view margin requires creating a RemoteUserControl and the corresponding data template for that control. While there are some simple examples below, we recommend reading the Remote UI documentation when creating text view margin UI content.

/// <summary>
/// Configures the margin to be placed to the left of built-in Visual Studio line number margin.
/// </summary>
public TextViewMarginProviderConfiguration TextViewMarginProviderConfiguration => new(marginContainer: ContainerMarginPlacement.KnownValues.BottomRightCorner)
{
    Before = new[] { MarginPlacement.KnownValues.RowMargin },
};

/// <summary>
/// Creates a remotable visual element representing the content of the margin.
/// </summary>
public async Task<IRemoteUserControl> CreateVisualElementAsync(ITextViewSnapshot textView, CancellationToken cancellationToken)
{
    var documentSnapshot = await textView.GetTextDocumentAsync(cancellationToken);
    var dataModel = new WordCountData();
    dataModel.WordCount = CountWords(documentSnapshot);
    this.dataModels[textView.Uri] = dataModel;
    return new MyMarginContent(dataModel);
}

In addition to configuring margin placement, text view margin providers can also configure the size of the grid cell in which the margin should be placed using GridCellLength and GridUnitType properties.

Text view margins typically visualize some data related to the text view (for example, current line number or the count of errors) so most text view margin providers would also want to listen to text view events to react to opening, closing of text views and user typing.

Visual Studio only creates one instance of your text view margin provider regardless of how many applicable text views a user opens, so if your margin displays some stateful data, your provider needs to keep the state of currently open text views.

For more information, see Word Count Margin Sample.

Vertical text view margins whose content needs to be aligned with text view lines are not yet supported.