AvalonEdit WPF TextEditor (SharpDevelop): How to highlight a specific range of text?

Question

The incredibly awesome AvalonEdit WPF TextEditor control seems to lack an important feature, or at least i can't figure it out. Given an offset and a length, highlight that portion in the TextDocument with a HighlightColor. Simple, right?

Apprentely not. I've RTFM, and the documentation on "Syntax Highlighting" confused me even more. Someone else asked the same question in the SharpDevelop forums, and i'm afraid i can't make sense of Herr Grunwald's answer.

Here's my attempt, using the DocumentHighlighter class (of course it doesn't work):

    textEditor1.Text = "1234567890";

    HighlightingColor c = new HighlightingColor() { FontWeight = FontWeights.ExtraBold };

    DocumentHighlighter dh = new DocumentHighlighter(textEditor1.Document, new HighlightingRuleSet());
    HighlightedLine hl = dh.HighlightLine(1);

    hl.Sections.Add(new HighlightedSection() { Color = c, Offset = 1, Length = 3 });

Thank you for helping!

Answer 1

Did you see this in this article - it seems to be exactly what are you asking for:

public class ColorizeAvalonEdit : DocumentColorizingTransformer
{
protected override void ColorizeLine(DocumentLine line)
{
    int lineStartOffset = line.Offset;
    string text = CurrentContext.Document.GetText(line);
    int start = 0;
    int index;
    while ((index = text.IndexOf("AvalonEdit", start)) >= 0) {
        base.ChangeLinePart(
            lineStartOffset + index, // startOffset
            lineStartOffset + index + 10, // endOffset
            (VisualLineElement element) => {
                // This lambda gets called once for every VisualLineElement
                // between the specified offsets.
                Typeface tf = element.TextRunProperties.Typeface;
                // Replace the typeface with a modified version of
                // the same typeface
                element.TextRunProperties.SetTypeface(new Typeface(
                    tf.FontFamily,
                    FontStyles.Italic,
                    FontWeights.Bold,
                    tf.Stretch
                ));
            });
        start = index + 1; // search for next occurrence
}   }   }

It highlights word AvalonEdit with bold.

Answer 2

Some background info: AvalonEdit is a code editor, not a rich text editor. There is no such thing as "highlight a portion of the document" - the document only stores plain text.

Highlighting is computed on-demand, only for the lines currently in view. If you want custom highlighting, you need to add a step to the highlighting computation - this is what the ColorizeAvalonEdit class in the example posted by mzabsky is doing.

Answer 3

You need to create a custom ColorizingTransformer to do that. The above example is actually highlighting a specific word. Still, you can change it a little bit to to colorize or highlight a portion.

I used Avalon TextEditor for my Console+ project (which is in a very primitive stage at the moment)

public class OffsetColorizer : DocumentColorizingTransformer
{
    public int StartOffset { get; set; }
    public int EndOffset { get; set; }

    protected override void ColorizeLine(DocumentLine line)
    {
        if (line.Length == 0)
            return;

        if (line.Offset < StartOffset || line.Offset > EndOffset)
            return;

        int start = line.Offset > StartOffset ? line.Offset : StartOffset;
        int end = EndOffset > line.EndOffset ? line.EndOffset : EndOffset;

        ChangeLinePart(start, end, element => element.TextRunProperties.SetForegroundBrush(Brushes.Red));
    }
}

And you can add the colorizer to the editor by adding it to LineTransformers collection.

tbxConsole.TextArea.TextView.LineTransformers.Add(_offsetColorizer);

Answer 4

I know this is a pretty old question, but I thought I would share my solution. I am not sure if this solution has been implemented into AvalonEdit, since this question was originally answered, but I find the OffsetColorizer class doesn't actually select the line: it just changes the line's background colour.

My solution is as follows:

textEditor.SelectionStart = offset;

textEditor.SelectionLength = length;

However, this can be extended further like so:

public void SelectText(int offset, int length)
{
    //Get the line number based off the offset.
    var line = textEditor.Document.GetLineByOffset(offset);
    var lineNumber = line.LineNumber;

    //Select the text.
    textEditor.SelectionStart = offset;
    textEditor.SelectionLength = length;

    //Scroll the textEditor to the selected line.
    var visualTop = textEditor.TextArea.TextView.GetVisualTopByDocumentLine(lineNumber);
    textEditor.ScrollToVerticalOffset(visualTop); 
}

I find that this solution works better is that rather than just colouring the line, it actually selects it: meaning it can be copied using Ctrl+C.

I Hope this helps people in the future.