RichTextBox syntax highlighting

Question

I am working with this code. It is for syntax highlighting in a RichTextBox. I am specifically looking at the function ProcessLine() and OnTextChanged(), which I have modified as such:

protected override void OnTextChanged(EventArgs e)
{
    // Calculate stuff here.
    m_nContentLength = this.TextLength;

    int nCurrentSelectionStart = SelectionStart;
    int nCurrentSelectionLength = SelectionLength;

    m_bPaint = false;

    // Find the start of the current line.
    m_nLineStart = nCurrentSelectionStart;
    while ((m_nLineStart > 0) && (Text[m_nLineStart - 1] != '\n'))
        m_nLineStart--;
    // Find the end of the current line.
    m_nLineEnd = nCurrentSelectionStart;
    while ((m_nLineEnd < Text.Length) && (Text[m_nLineEnd] != '\n'))
        m_nLineEnd++;
    // Calculate the length of the line.
    m_nLineLength = m_nLineEnd - m_nLineStart;
    // Get the current line.
    m_strLine = Text.Substring(m_nLineStart, m_nLineLength);

    // Process this line.
    ProcessLine();

    m_bPaint = true;
}

// Process a line.
private void ProcessLine()
{
    // Save the position and make the whole line black
    int nPosition = SelectionStart;
    SelectionStart = m_nLineStart;
    SelectionLength = m_nLineLength;
    SelectionColor = Color.Black;

    /*// Process the keywords
    ProcessRegex(m_strKeywords, Settings.KeywordColor);
    // Process numbers
    if(Settings.EnableIntegers)
        ProcessRegex("\\b(?:[0-9]*\\.)?[0-9]+\\b", Settings.IntegerColor);
    // Process strings
    if(Settings.EnableStrings)
        ProcessRegex("\"[^\"\\\\\\r\\n]*(?:\\\\.[^\"\\\\\\r\\n]*)*\"", Settings.StringColor);
    // Process comments
    if(Settings.EnableComments && !string.IsNullOrEmpty(Settings.Comment))
        ProcessRegex(Settings.Comment + ".*$", Settings.CommentColor);*/

    SelectionStart = nPosition;
    SelectionLength = 0;
    SelectionColor = Color.Red;

    m_nCurSelection = nPosition;
}

• My first question is, when I enter into the ProcessLine() in OnTextChanged(), will I always have a newline character at the end of m_strLine? Will the smallest value or m_strLine be "\n" and the largest "any#ofchars+\n"?

• And just so I have this right, SelectionStart is my caret position if SelectionLength is zero, and if SelectionLength is greater than zero my caret is at SelectStart+SelectionLength?

• I am trying to modify this code to color a whole lot of different syntax expressions, and I plan to go through it one character at a time, for each line. How might this fair when pasting or loading a file of 20k+ lines?

Answer 1

All I can suggest you right now is to use something stable, more powerful and less error prone such as Scintilla for .NET and Color Code. These controls are free and open source. Try them out:

ScintillaNET
ColorCode - Syntax Highlighting/Colorization for .NET

RichTextBox is extremely inefficient for working with large text. Even if you get some decent highlighting, the performance issues will start to pop up pretty soon.