How to change text color at ICSharpCode.AvalonEdit.TextEditor?

Question

Good day!

I am trying to make simple editor of code, so I want to be able to select the text line and change it color to red, using ICSharpCode.AvalonEdit.TextEditor.

But I do not know how to use it. Can you help me to change color of text line?

Thank you!

Answer 1

To select a line, use the Select() method:

var line = editor.Document.GetLineByOffset(lineOffset);
editor.Select(line.Offset, line.Length);

Changing the color of a line programatically is tricky tho, as AvalonEdit is a code editor, not a rich text editor, the coloring is mostly used for syntax highlighting. According to this post from the SharpDevelop forums, you should create a DocumentColorizingTransformer. Their example should work for you (I removed all error checking code for better readability):

class LineColorizer : DocumentColorizingTransformer
{
    int lineNumber;

    public LineColorizer(int lineNumber)
    {
        this.lineNumber = lineNumber;
    }

    protected override void ColorizeLine(ICSharpCode.AvalonEdit.Document.DocumentLine line)
    {
        if (!line.IsDeleted && line.LineNumber == lineNumber) {
            ChangeLinePart(line.Offset, line.EndOffset, ApplyChanges);
        }
    }

    void ApplyChanges(VisualLineElement element)
    {
        // This is where you do anything with the line
        element.TextRunProperties.SetForegroundBrush(Brushes.Red);
    }
}

Then, to apply it for your document, you can use it as follows:

editor.TextArea.TextView.LineTransformers.Add(new LineColorizer(lineOffset));