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：
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////// 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：
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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。
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重写WriteStartElementis以避免不被允许的标签写到输出中。
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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：
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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
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
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////// 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
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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
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bool canWrite = false;string attributeLocalName = reader.LocalName.ToLower();foreach( string name in this.AllowedAttributes ){ if( name == attributeLocalName ) { canWrite = true; break; }}// If allowed, write the attributeif( 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：http://www.codeproject.com/Articles/10792/Convert-HTML-to-XHTML-and-Clean-Unnecessary-Tags-a