Prevent scrollbar position from being changed in richtextbox?

Question

I have the following code:

    private void HighlightSyntax(string syntax)
    {
        Regex regex = null;

        switch (syntax)
        {
            case ".xml":
                regex = new Regex(@"<\/?[^>\/]*>");
                break;
        }

        if (regex != null)
        {
            Input.BeginUpdate();

            // I want to save scrollbar position here and then restore it
            // or maybe even disable it from being changed

            int lastIndex = Input.SelectionStart;
            int lastLength = Input.SelectionLength;

            Input.SelectAll();

            // gets matches
            var matches = regex.Matches(Input.Text).Cast().ToArray();
            if (matches.Length > 0) // divide into tasks and select all matches
            {
                Color color = Color.ForestGreen;
                int wordsPerTask = 500;
                int tasksAmount = (matches.Length / wordsPerTask) + 1;
                int start = 0;
                int end = matches.Length - 1;

                Task[] tasks = new Task[tasksAmount];
                for (int i = 0; i < tasksAmount; i++)
                { // dividing
                    start = matches.Length / tasksAmount * i;
                    end = matches.Length / tasksAmount * (i + 1) - 1;

                    var start1 = start;
                    var end1 = end;
                    tasks[i] = Task.Run(() => { SelectMatchesInArr(matches, start, end, color); } );
                }

                if (matches.Length - 1 - end > 0)
                    SelectMatchesInArr(matches, end + 1, matches.Length - 1, color);

                Task.WaitAll(tasks);
            }

            Input.Select(lastIndex, lastLength);
            Input.SelectionColor = Color.Black;

            // Restore Input.ScrollBarPosition here

            Input.EndUpdate();
        }
    }

    // selects matches from start to end Indexes with Color color.
    private void SelectMatchesInArr(Match[] matches, int startIndex, int endIndex, Color color)
    {
        for (int i = startIndex; i <= endIndex; i++)
        {
            int selectionStart = Input.SelectionStart;

            lock (_locker)
            {
                Input.Select(matches[i].Index, matches[i].Length);
                Input.SelectionColor = color;

                Input.DeselectAll();
                Input.SelectionStart = selectionStart;
                Input.SelectionLength = 0;
            }
        }
    }

It highlights syntax in richtexbox, if regex matches anything related to that syntax. It all worked until I decided to divide selecting into multiple tasks.

After dividing the selection into multiple tasks, my scrollbar position is not stable. Well, I want it to be stable, I don't want it to be changed via code. How do I prevent it from being changed if I have multiple tasks manipulating over richtextbox? What should I do in my situation? Also check comments in the code, they are written in order to help you explain what I want to do.

By the way, the BeginUpdate() and EndUpdate() methods are extension methods that have been taken from here: Hans Passant's derived from richtextbox class

Prevent scrollbar position from being changed in richtextbox?

Answers (1)

Related Questions