In case you want to display HTML with highlighted/colored syntax the simplest way to go is use WinForms RichTextBox, all is needed is to add RTF color tags surrounding HTML elements.
This helper class goal is exactly that, given a string containing HTML code it will return an RTF formatted string with the HTML elements colored.
I have used Alun Evans code as base, improving its coloring support and performance.
See it's usage in HtmlRenderer project.
Features
- Rich coloring adjusted to Visual Studio HTML coloring.
- Support to for 6 custom colors – element, attribute, comment, chars, values, style.
- Handle plain input – HTML text without not in RTF format.
- Handle RTF formatted input – text that has already in RTF format that just need coloring.
- Handle if input already contains RTF color table.
- High performance (as much as RTF format allows).
Sample
Code
/// <summary>
/// HTML syntax highlighting using Rich-Text formatting.<br/>
/// - Handle plain input or already in RTF format.<br/>
/// - Handle if input already contains RTF color table.<br/>
/// - Rich coloring adjusted to Visual Studio HTML coloring.<br/>
/// - Support to provide custom colors.<br/>
/// - High performance (as much as RTF format allows).<br/>
/// </summary>
/// <remarks>
/// The MIT License (MIT) Copyright (c) 2014 Arthur Teplitzki.<br/>
/// Based on work by Alun Evans 2006 (http://www.codeproject.com/Articles/15038/C-Formatting-Text-in-a-RichTextBox-by-Parsing-the).
/// </remarks>
public static class HtmlSyntaxHighlighter
{
#region Fields/Consts
/// <summary>
/// RTF header field
/// </summary>
private const string Header = "rtf";
/// <summary>
/// RTF color table
/// </summary>
private const string ColorTbl = "colortbl";
/// <summary>
/// cf0 = default
/// cf1 = dark red
/// cf2 = bright red
/// cf3 = green
/// cf4 = blue
/// cf5 = blue
/// cf6 = purple
/// </summary>
private const string DefaultColorScheme = "red128green0blue0;red240green0blue0;red0green128blue0;red0green0blue255;red0green0blue255;red128green0blue171;";
/// <summary>
/// Used to test if a char requires more than 1 byte
/// </summary>
private static readonly char[] _unicodeTest = new char[1];
#endregion
/// <summary>
/// Process the given text to create RTF text with HTML syntax highlighting using default Visual Studio colors.<br/>
/// The given text can be plain HTML or already parsed RTF format.
/// </summary>
/// <param name="text">the text to create color RTF text from</param>
/// <returns>text with RTF formatting for HTML syntax</returns>
public static string Process(string text)
{
return Process(text, DefaultColorScheme);
}
/// <summary>
/// Process the given text to create RTF text with HTML syntax highlighting using custom colors.<br/>
/// The given text can be plain HTML or already parsed RTF format.
/// </summary>
/// <param name="text">the text to create color RTF text from</param>
/// <param name="element">the color for HTML elements</param>
/// <param name="attribute">the color for HTML attributes</param>
/// <param name="comment">the color for HTML comments</param>
/// <param name="chars">the color for HTML special chars: (<![CDATA[<,>,",',=,:]]>)</param>
/// <param name="values">the color for HTML attribute or styles values</param>
/// <param name="style">the color for HTML style attribute</param>
/// <returns>text with RTF formatting for HTML syntax</returns>
public static string Process(string text, Color element, Color attribute, Color comment, Color chars, Color values, Color style)
{
return Process(text, CreateColorScheme(element, attribute, comment, chars, values, style));
}
#region Private/Protected methods
/// <summary>
/// Process the given text to create RTF text with HTML syntax highlighting.
/// </summary>
/// <param name="text">the text to create color RTF text from</param>
/// <param name="colorScheme">the color scheme to add to RTF color table</param>
/// <returns>text with RTF formatting for HTML syntax</returns>
private static string Process(string text, string colorScheme)
{
var sb = new StringBuilder(text.Length * 2);
// add color table used to set color in RTL formatted text
bool rtfFormated;
int i = AddColorTable(sb, text, colorScheme, out rtfFormated);
// Scan through RTF data adding RTF color tags
bool inComment = false;
bool inHtmlTag = false;
bool inAttributeVal = false;
for (; i < text.Length; i++)
{
var c = text[i];
var c2 = text.Length > i + 1 ? text[i + 1] : (char)0;
if (!inComment && c == '<')
{
if (text.Length > i + 3 && c2 == '!' && text[i + 2] == '-' && text[i + 3] == '-')
{
// Comments tag
sb.Append("cf3").Append(c);
inComment = true;
}
else
{
// Html start/end tag
sb.Append("cf4").Append(c);
if (c2 == '/')
{
sb.Append(c2);
i++;
}
sb.Append("cf1 ");
inHtmlTag = true;
}
}
else if (c == '>')
{
//Check for comments tags
if (inComment && text[i - 1] == '-' && text[i - 2] == '-')
{
sb.Append(c).Append("cf0 ");
inComment = false;
}
else if (!inComment)
{
sb.Append("cf4").Append(c).Append("cf0 ");
inHtmlTag = false;
inAttributeVal = false;
}
}
else if (inHtmlTag && !inComment && c == '/' && c2 == '>')
{
sb.Append("cf4").Append(c).Append(c2).Append("cf0 ");
inHtmlTag = false;
i++;
}
else if (inHtmlTag && !inComment && !inAttributeVal && c == ' ')
{
sb.Append(c).Append("cf2 ");
}
else if (inHtmlTag && !inComment && c == '=')
{
sb.Append("cf4").Append(c).Append("cf6 ");
}
else if (inHtmlTag && !inComment && inAttributeVal && c == ':')
{
sb.Append("cf0").Append(c).Append("cf5 ");
}
else if (inHtmlTag && !inComment && inAttributeVal && c == ';')
{
sb.Append("cf0").Append(c).Append("cf6 ");
}
else if (inHtmlTag && !inComment && (c == '"' || c == '''))
{
sb.Append("cf4").Append(c).Append("cf6 ");
inAttributeVal = !inAttributeVal;
}
else if (!rtfFormated && c == 'n')
{
sb.Append(c).Append("par ");
}
else if (!rtfFormated && (c == '{' || c == '}'))
{
sb.Append('').Append(c);
}
else if (!rtfFormated)
{
_unicodeTest[0] = c;
if (Encoding.UTF8.GetByteCount(_unicodeTest, 0, 1) > 1)
sb.Append("u" + Convert.ToUInt32(c) + "?");
else
sb.Append(c);
}
else
{
sb.Append(c);
}
}
// close the RTF if we added the header ourselves
if (!rtfFormated)
sb.Append('}');
// return the created colored RTF
return sb.ToString();
}
/// <summary>
/// Add color table used to set color in RTL formatted text.
/// </summary>
/// <param name="sb">the builder to add the RTF string to</param>
/// <param name="text">the original RTF text to build color RTF from</param>
/// <param name="colorScheme">the color scheme to add to RTF color table</param>
/// <param name="rtfFormated">return if the given text is already in RTF format</param>
/// <returns>the index in the given RTF text to start scan from</returns>
private static int AddColorTable(StringBuilder sb, string text, string colorScheme, out bool rtfFormated)
{
// Search for color table, if exists replace it, otherwise add our
rtfFormated = true;
int idx = text.IndexOf(ColorTbl, StringComparison.OrdinalIgnoreCase);
if (idx != -1)
{
sb.Append(text, 0, idx);
// insert our color table at our chosen location
sb.Append(ColorTbl).Append(";").Append(colorScheme).Append("}");
// skip the existing color table
idx = text.IndexOf('}', idx);
}
else
{
// find index of start of header if exists
idx = text.IndexOf(Header, StringComparison.OrdinalIgnoreCase);
if (idx != -1)
{
// append the existing header
idx += Header.Length;
sb.Append(text, 0, idx);
while (text[idx] != '' && text[idx] != '{' && text[idx] != '}')
sb.Append(text[idx++]);
}
else
{
// not RTF text, add the RTF header as well
idx = 0;
sb.Append("{").Append(Header);
rtfFormated = false;
}
// insert the color table at our chosen location
sb.Append("{").Append(ColorTbl).Append(";").Append(colorScheme).Append("}");
}
return idx;
}
/// <summary>
/// Create RTF colortbl formatted string for the given colors.
/// </summary>
private static string CreateColorScheme(Color element, Color attribute, Color comment, Color chars, Color values, Color style)
{
var sb = new StringBuilder(DefaultColorScheme.Length);
AppendColorValue(sb, element);
AppendColorValue(sb, attribute);
AppendColorValue(sb, comment);
AppendColorValue(sb, chars);
AppendColorValue(sb, values);
AppendColorValue(sb, style);
return sb.ToString();
}
/// <summary>
/// Append single color in RTF colortbl format.
/// </summary>
private static void AppendColorValue(StringBuilder sb, Color color)
{
sb.Append("red").Append(color.R)
.Append("green").Append(color.R)
.Append("blue").Append(color.R)
.Append(';');
}
#endregion
}
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