Syntax highlighting in richtextbox

Question

How do i highlight the CSS keywords in richtextbox using c#?

I had css parser to split the selector, property and value and used following code for this purpose,

        CssParser parser = new CssParser();

            var rules = parser.ParseAll(RichEditor.Text);

            StringBuilder selectorBuilder = new StringBuilder();

            StringBuilder propertyBuilder = new StringBuilder();

            StringBuilder ValueBuilder = new StringBuilder();

            Regex selectorRegex, mediaRegex, propertyRegex, valueRegex;

            int cursorPosition = RichEditor.SelectionStart;

            int lineIndex = RichEditor.GetLineFromCharIndex(cursorPosition);

            foreach (var rule in rules)

            {

                foreach (var selector in rule.Selectors)

                {

                  

                    selectorBuilder.Append(selector.ToString() + "|");

                }

                if (rule.Media != null)

                {

                    mediaBuilder.Append(rule.Media.ToString() + "|");

                }

                foreach (var declaration in rule.Declarations)

                {

                    propertyBuilder.Append(declaration.Property.ToString() + "|");

                    ValueBuilder.Append(declaration.Value.ToString() + "|");

                }

            }

            selectorRegex = new Regex(selectorBuilder.ToString());

            mediaRegex = new Regex(mediaBuilder.ToString());

            propertyRegex = new Regex(propertyBuilder.ToString());

            valueRegex = new Regex(ValueBuilder.ToString());

            // Select all and set to black so that it's 'clean'

            RichEditor.SelectAll();

            RichEditor.SelectionColor = System.Drawing.Color.Black;

            // Then unselect and scroll to the end of the file

            RichEditor.ScrollToCaret();

            RichEditor.Select(RichEditor.Text.Length, 1);

            // Start applying the highlighting... Set a value to selPos

            int selPos = RichEditor.SelectionStart;

            foreach (Match keyWordMatch in selectorRegex.Matches(RichEditor.Text))

            {

              

                RichEditor.Select(keyWordMatch.Index, keyWordMatch.Length);

             

                RichEditor.SelectionColor = System.Drawing.Color.Brown;

              

                RichEditor.SelectionStart = selPos;

                

            }

            selPos = RichEditor.SelectionStart;

            foreach (Match keyWordMatch in mediaRegex.Matches(RichEditor.Text))

            {

              

                RichEditor.Select(keyWordMatch.Index, keyWordMatch.Length);

              

                RichEditor.SelectionColor = System.Drawing.Color.Red;

              

                RichEditor.SelectionStart = selPos;

               

            }

            selPos = RichEditor.SelectionStart;

            foreach (Match keyWordMatch in propertyRegex.Matches(RichEditor.Text))

            {

               

                RichEditor.Select(keyWordMatch.Index, keyWordMatch.Length);

          

                RichEditor.SelectionColor = System.Drawing.Color.Red;

               

                RichEditor.SelectionStart = selPos;

               

            }

            selPos = RichEditor.SelectionStart;

            foreach (Match keyWordMatch in valueRegex.Matches(RichEditor.Text))

            {

         

                RichEditor.Select(keyWordMatch.Index, keyWordMatch.Length);

       

                RichEditor.SelectionColor = System.Drawing.Color.Blue;

             

                RichEditor.SelectionStart = selPos;

              

                RichEditor.SelectionColor = System.Drawing.Color.Black;

            } 

 

But every time the text in richtextbox is flickering.

Is there any solution for this purpose?