Exception while using Regex with richtextbox in C#

Question

I am making Richtextbox Editor with Regex to format few specific words. I am using below code:

private void myrichTextBox1_TextChanged(object sender, EventArgs e)
    {
        // getting keywords/functions
        string keywords = @"\b(public|private|sendln|static|namespace|Wait|using|void|foreach|in|OK|ERROR)\b";
        MatchCollection keywordMatches = Regex.Matches(richTextBox1.Text, keywords);

        // getting types/classes from the text 
        string types = @"\b(Console)\b";
        MatchCollection typeMatches = Regex.Matches(richTextBox1.Text, types);

        // getting comments (inline or multiline)
        string comments = @"(\/\/.+?$|\/\*.+?\*\/)";
        MatchCollection commentMatches = Regex.Matches(richTextBox1.Text, comments, RegexOptions.Multiline);

        // getting strings
        string strings = "\".+?\"";
        MatchCollection stringMatches = Regex.Matches(richTextBox1.Text, strings);


        // saving the original caret position + forecolor
        int originalIndex = richTextBox1.SelectionStart;
        int originalLength = richTextBox1.SelectionLength;
        Color originalColor = Color.Black;

        // MANDATORY - focuses a label before highlighting (avoids blinking)

          titleLabel.Focus();

        // removes any previous highlighting (so modified words won't remain highlighted)
        richTextBox1.SelectionStart = 0;
        richTextBox1.SelectionLength = richTextBox1.Text.Length;
        richTextBox1.SelectionColor = originalColor;


        // scanning...
        foreach (Match m in keywordMatches)
        {
            richTextBox1.SelectionStart = m.Index;
            richTextBox1.SelectionLength = m.Length;
            richTextBox1.SelectionColor = Color.Blue;
        }


        foreach (Match m in typeMatches)
        {
            richTextBox1.SelectionStart = m.Index;
            richTextBox1.SelectionLength = m.Length;
            richTextBox1.SelectionColor = Color.DarkCyan;
        }

        foreach (Match m in commentMatches)
        {
            richTextBox1.SelectionStart = m.Index;
            richTextBox1.SelectionLength = m.Length;
            richTextBox1.SelectionColor = Color.Green;
        }

        foreach (Match m in stringMatches)
        {
            richTextBox1.SelectionStart = m.Index;
            richTextBox1.SelectionLength = m.Length;
            richTextBox1.SelectionColor = Color.Brown;
        }

        // restoring the original colors, for further writing
        richTextBox1.SelectionStart = originalIndex;
        richTextBox1.SelectionLength = originalLength;
        richTextBox1.SelectionColor = originalColor;

        // giving back the focus
        richTextBox1.Focus();
    }

Since there was continous flickering on text edit, hence moved the focus to label titleLabel.Focus();. But on launch, its giving below exception:

An unhandled exception of type 'System.StackOverflowException' occurred in System.Windows.Forms.dll.

Without titleLabel.Focus(); there is no Exception but Continous Blinking.

Changing selection attributes in a TextChanged event causes a TextChanged event which changes selection attributes which causes a TextChanged event ... ad infinitum. See [WinForms RichTextBox : how to reformat asynchronously, without firing TextChanged event](http://stackoverflow.com/questions/1457411/winforms-richtextbox-how-to-reformat-asynchronously-without-firing-) — Alex K., Nov 06 '14 at 13:24
Thanks Yuriy for proper formating. @ Alex, Still i am confused for the solution. — anupam.unique, Nov 06 '14 at 13:28

score 1 · Accepted Answer · answered Nov 06 '14 at 18:08

The best thing would probably be to change your formatting code so that it first figures out if any changes to the text actually need to be made, and only apply changes to the contents of the text box if they do. This approach also improves efficiency of the control by avoiding unnecessary updates.

An alternative, somewhat hacky but far easier to implement, would be to set a flag when you are in the middle of handling the event, so that if the event is raised again you know to ignore the event. For example:

private bool _updatingTextBox;

private void myrichTextBox1_TextChanged(object sender, EventArgs e)
{
    if (_updatingTextBox)
    {
        return;
    }

    _updatingTextBox = true;

    try
    {
       // all your updating code goes here
    }
    finally
    {
        _updatingTextBox = false;
    }
}

Exception while using Regex with richtextbox in C#

1 Answers1