介绍
这是一个能帮你从HTML生成有效XHTML的经典库。它还提供对标签以及属性过滤的支持。你可以指定允许哪些标签和属性可在出现在输出中，而其他的标签过滤掉。你也可以使用这个库清理Microsoft Word文档转化成HTML时生成的臃肿的HTML。你也在将HTML发布到博客网站前清理一下，否则像WordPress、b2evolution等博客引擎会拒绝的。
它是如何工作的
里面有两个类：HtmlReader和HtmlWriter
HtmlReader拓展了著名的由Chris Clovett开发的SgmlReader。当它读取HTML时，它跳过所有有前缀的节点。其中，所有像<o:p>、<o:Document>、<st1:personname>等上百的无用标签被滤除了。这样你读取的HTML就剩下核心的HTML标签了。
HtmlWriter拓展了常规的XmlWriter，XmlWriter生成XML。XHTML本质上是XML格式的HTML。所有你熟悉使用的标签——比如<img>、<br>和<hr>，都不是闭合的标签——在XHTML中必需是空元素形式，像<img .. />、<br/>和<hr/>。由于XHTML是常见的XML格式，你可以方便的使用XML解析器读取XHTML文档。这使得有了应用XPath搜索的机会。
HtmlReader
HtmlReader很简单，下面是完整的类：
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 | // This class skips all nodes which has some /// kind of prefix. This trick does the job /// to clean up MS Word/Outlook HTML markups. ///public class HtmlReader : Sgml.SgmlReader { public HtmlReader( TextReader reader ) : base( ) { base.InputStream = reader; base.DocType = "HTML" ; } public HtmlReader( string content ) : base( ) { base.InputStream = new StringReader( content ); base.DocType = "HTML" ; } public override bool Read() { bool status = base.Read(); if ( status ) { if ( base.NodeType == XmlNodeType.Element ) { // Got a node with prefix. This must be one // of those "" or something else. // Skip this node entirely. We want prefix // less nodes so that the resultant XML // requires not namespace. if ( base.Name.IndexOf( ':' ) > 0 ) base.Skip(); } } return status; } } |
HtmlWriter
这个类是有点麻烦。下面是使用技巧：
-
重写WriteString方法并避免使用常规的XML编码。对HTML文件手动更改编码。
-
重写WriteStartElementis以避免不被允许的标签写到输出中。
-
重写WriteAttributesis以避免不需求的属性。
让我们分部分来看下整个类：
可配置性
你可以通过修改下面的部分配置HtmlWriter：
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 | public class HtmlWriter : XmlTextWriter { // If set to true, it will filter the output /// by using tag and attribute filtering, /// space reduce etc ///public bool FilterOutput = false; // If true, it will reduce consecutive with one instance ///public bool ReduceConsecutiveSpace = true; // Set the tag names in lower case which are allowed to go to output ///public string [] AllowedTags = new string[] { "p" , "b" , "i" , "u" , "em" , "big" , "small" , "div" , "img" , "span" , "blockquote" , "code" , "pre" , "br" , "hr" , "ul" , "ol" , "li" , "del" , "ins" , "strong" , "a" , "font" , "dd" , "dt" }; // If any tag found which is not allowed, it is replaced by this tag. /// Specify a tag which has least impact on output ///public string ReplacementTag = "dd"; // New lines \r\n are replaced with space /// which saves space and makes the /// output compact ///public bool RemoveNewlines = true; // Specify which attributes are allowed. /// Any other attribute will be discarded ///public string [] AllowedAttributes = new string[] { "class" , "href" , "target" , "border" , "src" , "align" , "width" , "height" , "color" , "size" }; } |
WriteString方法
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 | // The reason why we are overriding /// this method is, we do not want the output to be /// encoded for texts inside attribute /// and inside node elements. For example, all the /// gets converted to   in output. But this does not /// apply to HTML. In HTML, we need to have as it is. //public override void WriteString(string text) { // Change all non-breaking space to normal space text = text.Replace( " " , " " ); /// When you are reading RSS feed and writing Html, /// this line helps remove those CDATA tags text = text.Replace( "" , "" ); // Do some encoding of our own because // we are going to use WriteRaw which won't // do any of the necessary encoding text = text.Replace( "<" , "<" ); text = text.Replace( ">" , ">" ); text = text.Replace( "'" , "'" ); text = text.Replace( "\"" , "" e;" ); if ( this .FilterOutput ) { text = text.Trim(); // We want to replace consecutive spaces // to one space in order to save horizontal width if ( this .ReduceConsecutiveSpace ) text = text.Replace( " " , " " ); if ( this .RemoveNewlines ) text = text.Replace(Environment.NewLine, " " ); base.WriteRaw( text ); } else { base.WriteRaw( text ); } } |
WriteStartElement: 应用标签过滤
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 | public override void WriteStartElement(string prefix, string localName, string ns) { if ( this .FilterOutput ) { bool canWrite = false ; string tagLocalName = localName.ToLower(); foreach( string name in this .AllowedTags ) { if ( name == tagLocalName ) { canWrite = true ; break ; } } if ( !canWrite ) localName = "dd" ; } base.WriteStartElement(prefix, localName, ns); } |
WriteAttributes方法: 应用属性过滤
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 | bool canWrite = false ; string attributeLocalName = reader.LocalName.ToLower(); foreach( string name in this .AllowedAttributes ) { if ( name == attributeLocalName ) { canWrite = true ; break ; } } // If allowed, write the attribute if ( canWrite ) this .WriteStartAttribute(reader.Prefix, attributeLocalName, reader.NamespaceURI); while (reader.ReadAttributeValue()) { if (reader.NodeType == XmlNodeType.EntityReference) { if ( canWrite ) this .WriteEntityRef(reader.Name); continue ; } if ( canWrite ) this .WriteString(reader.Value); } if ( canWrite ) this .WriteEndAttribute(); |
结论
示例应用是一个你可以立即用来清理HTML文件的实用工具。你可以将这个类应用在像博客等需要发布一些HTML到Web服务的工具中。
原文地址：