richtextbox - C# writing a code editor issues -

so i'm writing simple code editor language like. have syntax hilighting going well. problem if go before text have written, screws whole hilighting past pointer. here code, apologies posting much:

public partial class form1 : form {     public string mainfontname = "courier new";     public int mainfontsize = 12;     public color mainfontcolor = color.black;      [dllimport("user32.dll")] // import lockwindow remove flashing     public static extern bool lockwindowupdate(intptr hwndlock);       public regex codefunctions = new regex("draw_line|draw_rectangle|draw_circle");     public regex codekeywords = new regex("and|for|while|repeat|or|xor|exit|break|case|switch|if|then|with|true|false");      public form1()     {         initializecomponent();          codeinput.font = new font(mainfontname, mainfontsize, fontstyle.regular);     }      private void codeinput_textchanged(object sender, eventargs e)     {         codeinput.font = new font(mainfontname, mainfontsize, fontstyle.regular);         try         {             lockwindowupdate(codeinput.handle);              int selpos = codeinput.selectionstart;              codeinput.select(0, codeinput.textlength);             codeinput.selectionfont = new font(mainfontname, mainfontsize, fontstyle.regular);             codeinput.selectioncolor = color.black;             codeinput.selectionlength = 0;             codeinput.selectionstart = selpos;              //match functions             foreach (match keywordmatch in codefunctions.matches(codeinput.text))             {                  codeinput.select(keywordmatch.index, keywordmatch.length);                 codeinput.selectioncolor = color.red;                  codeinput.selectionstart = selpos;                 codeinput.selectioncolor = mainfontcolor;                  codeinput.selectionlength = 0;             }             // match keywords             foreach (match keywordmatch in codekeywords.matches(codeinput.text))             {                  font ofont = new font(mainfontname, mainfontsize, fontstyle.bold);                 font nfont = new font(mainfontname, mainfontsize, fontstyle.regular);                  codeinput.select(keywordmatch.index, keywordmatch.length);                 codeinput.selectioncolor = color.blue;                 codeinput.selectionfont = ofont;                  codeinput.selectionstart = selpos;                 codeinput.selectioncolor = mainfontcolor;                 codeinput.selectionfont = nfont;                  codeinput.selectionlength = 0;             }         }                 {             lockwindowupdate(intptr.zero);         }     } } 

thanks help.

you on right track try blocking wm_paint instead of using api calls,i have worked on type of project , implemented syntax highlighting successfully,its original source code below;

///radoncodeeditor name of project     /// <summary>     /// gets or sets value whether radontexteditor should repaint itself.     /// </summary>     public bool repaint = true; ckeyword=color.blue; ccomment=color.green;      /// <summary>     /// windows generated message send control needs repainting.     /// </summary>     const short wm_paint = 0x00f;      /// <summary>     /// contains creation data call radontexteditor.     /// </summary>     public radontexteditor()     {         setstyle(controlstyles.optimizeddoublebuffer, true);//reduces flickering.     }      /// <summary>     /// overrides default wndproc , handles wm_paint message remove flickering.     /// </summary>     /// <param name="m">the message in message queue.</param>     protected override void wndproc(ref message m)     {         if (m.msg == wm_paint)//if message in message queue wm_paint.         {             switch (repaint)             {                 case true://when want radontexteditor repaint.                     base.wndproc(ref m);                     break;                  case false://when don't want radontexteditor repaint.                     m.result = intptr.zero;                     break;             }         }         else//if message in message queue else not wm_paint.         {             base.wndproc(ref m);         }     } //import namespace system.text.regularexpressions  /// <summary>     /// checks input text contained comments using defined regular expression.     /// </summary>     /// <param name="text">the text check.</param>     /// <param name="firstcharindex">the first character index of current line.</param>     /// <param name="caretposition">the position of caret.</param>     /// <param name="rtb">the handle richtextbox highlighting.</param>     /// <returns>if input text contains text return value true otherwise false.</returns>     public void iscomment(string text, int firstcharindex, int caretposition, richtextbox rtb)     {         rcomment = new regex(@"\/\/.*$", regexoptions.compiled);         matchcollection matches = rcomment.matches(text);         foreach (match match in matches)         {             rtb.select(match.index + firstcharindex, match.length);             rtb.selectioncolor = ccomment;             rtb.deselectall();             rtb.selectionstart = caretposition;          }         rmulticomment = new regex(@"/\*.*?\*/", regexoptions.multiline);         matchcollection matches2 = rmulticomment.matches(text);         foreach (match match2 in matches2)         {             rtb.select(match2.index + firstcharindex, match2.length);             rtb.selectioncolor = ccomment;             rtb.deselectall();             rtb.selectionstart = caretposition;         }     }      /// <summary>     /// checks input text contained keywords using defined regular expression.     /// </summary>     /// <param name="text">the text check.</param>     /// <param name="firstcharindex">the first character index of current line.</param>     /// <param name="caretposition">the position of caret.</param>     /// <param name="rtb">the handle richtextbox highlighting.</param>     /// <returns>if input text contains text return value true otherwise false.</returns>     public void iskeyword(string text, int firstcharindex, int caretposition, richtextbox rtb)     {         rkeyword = new regex(@:\bint\b|\bdouble\b|\bstring\b", regexoptions.compiled);         matchcollection matches = rkeyword.matches(text);         foreach (match match in matches)         {             rtb.select(match.index + firstcharindex, match.length);             rtb.selectioncolor = ckeyword;             rtb.deselectall();             rtb.selectionstart = caretposition;         }     } 

that's it,call both functions in textchange event handler , pass required arguments functions described comments(i know it's bit messy because have directly pasted source code project have.)if still goes wrong i'll glad you.