在RichTextBox中格式化文本时的性能问题

Question

I'm creating an editor with simple syntax highlighting using RichTextBox. The process of highlighting itself is implemented using following function:

        TextRange documentRange = new TextRange(rtb.Document.ContentStart, rtb.Document.ContentEnd);
        documentRange.ClearAllProperties();

        .......

        tags.Sort((i, j) => i.Level > j.Level ? 1 : i.Level == j.Level ? 0 : -1);
        Color []_colors=new Color[]{Colors.Blue,Colors.Brown,Colors.BlueViolet,Colors.Crimson,Colors.DarkBlue,
            Colors.Green,Colors.DimGray,Colors.DarkGray,Colors.Maroon,Colors.Navy,Colors.Red};
        foreach (var tag in tags)
        {
            TextRange range = new TextRange(tag.StartPosition, tag.EndPosition);
            range.ApplyPropertyValue(TextElement.ForegroundProperty, new SolidColorBrush(_colors[tag.Level%_colors.Length]));
            range.ApplyPropertyValue(TextElement.FontWeightProperty, FontWeights.Bold);
        }

The problem is, that when I use this approach, when there are a lot of keywords in text, the application's performance suffers significantly, especially that I'm doing this every time RichTextBoxe's text changes.

I run the profiler, and in seems that the application spends half of its processor time in documentRange.ClearAllProperties().

What should I change to improve the permanence of the application?

Can anyone provide a good example of fast syntax highlighting using WPF RichTextBox?

Answer 1

One thing that I would recommend that might help, but probably won't be a complete solution, is to use a timer to call your syntax highlighting code. Something like: (psuedo-code)

OnRichTextChanged() 
{
   StopExisingSyntaxHighlighterTimer();
   StartSyntaxHighlighterTimer(TimeSpan.FromSeconds(5));
}

OnSyntaxHighlighterTimerFired() 
{
   StopExisingSyntaxHighlighterTimer();
   DoSyntaxHighlighting();
}

The idea that you're only doing the syntax highlighting when the user pauses for 5 seconds or more, that way you're not trying to re-highlight the entire RichTextBox with every single key stroke.

Also, you might even take this one step further and actually make the DoSyntaxHighlighting cancellable so that if it starts doing the highlighting and the user starts typing again, the highlighter stops processing and waits for the user to stop typing again.

This might look a little funky, since the highlighting will disappear and reappear as they're typing and stopping. But it will definitely improve performance.

You can also look at something like AvalonEdit .