c# - Syntax Highlighting performance issue -

i have richtextbox , once user loads file, program proceeds scan entire file in order change color of words. here code:

static regex ckeywords = new regex(@"\b(?=[a-gilr-w])(?:      s(?:hort|i(?:gned|zeof)|t(?:atic|ruct)|witch) | c(?:ase|har|on(?:st|tinue)) |      e(?:lse|num|xtern) | i(?:f|nt) | f(?:loat|or) | d(?:o|efault|ouble) | un(?:ion|signed) |      re(?:gister|turn) | vo(?:id|latile) | while | break | long | typedef | auto | goto      )\b",      regexoptions.compiled | regexoptions.ignorepatternwhitespace);  ...  programtextbox.enabled = false; int selectstart = this.programtextbox.selectionstart; programtextbox.suspendlayout(); matchcollection matches = ckeywords.matches(programtextbox.text); foreach (match match in matches) {     if (match.index == 0)         programtextbox.select(match.index, match.length/* - 1*/);     else         programtextbox.select(match.index + 1, match.length - 1);     programtextbox.selectioncolor = color.blue; } programtextbox.select(selectstart, 0); programtextbox.selectioncolor = color.black; programtextbox.enabled = true; programtextbox.resumelayout(); 

problem: code takes 5 , half seconds scan , change colors of keywords in file has 200,000 characters.

i've been told before shouldn't use regex kind of stuff, after doing several tests figured out the: matchcollection matches = ckeywords.matches(programtextbox.text);

only takes 0.1s , removing the

programtextbox.selectioncolor = color.blue; 

reduces total execution time of code 5.5s 0.3s

how? why? , importantly: can do?

have tried this?

this blocks painting , seems block properly. had small test file put through it, seemed work pretty well.