想要一個正則表達式的匹配函數，但是XPath1.0中間沒有，
只好自己擴展一個，在網上搜了一下，有一篇文章不錯，
http://www.microsoft.com/china/MSDN/library/data/xml/AddingCustomFunctionstoXpath.mspx?mfr=true
該文章定義了一個split,一個replace,不過就是沒有match,
只好在它的基礎上，擴展一下

仔細觀察一下代碼，發現想要擴展一個函數很簡單，只要修改這幾段就好了：

1：CustomContext.cs

//?Function?to?resolve?references?to?my?custom?functions.
????????public?override?IXsltContextFunction?ResolveFunction(string?prefix,
?????string?name,?XPathResultType[]?ArgTypes)
????????{
????????????XPathRegExExtensionFunction?func?=?null;
????????????//?Create?an?instance?of?appropriate?extension?function?class.
????????????switch?(name)
????????????{
????????????????case?"Match":
????????????????????//?Usage?
????????????????????//?myFunctions:Matches(string?source,?string?Regex_pattern)?returns?Boolean
????????????????????func?=?new?XPathRegExExtensionFunction("Match",?2,?2,?new
????????XPathResultType[]?{XPathResultType.String,?XPathResultType.String}
????????,?XPathResultType.Boolean?);
????????????????????break;
????????????????case?"Split":
????????????????????//?Usage?
????????????????????//?myFunctions:Split(string?source,?string?Regex_pattern,?int?n)?returns?string
????????????????????func?=?new?XPathRegExExtensionFunction("Split",?3,?3,?new
????????XPathResultType[]?{XPathResultType.String,?XPathResultType.String,?
XPathResultType.Number},?XPathResultType.String);
????????????????????break;
????????????????case?"Replace":
????????????????????//?Usage
????????????????????//?myFunctions:Replace(string?source,?string?Regex_pattern,?string?replacement_string)?returns?string
????????????????????func?=?new?XPathRegExExtensionFunction("Replace",?3,?3,?new
????????XPathResultType[]?{XPathResultType.String,?XPathResultType.String,?
XPathResultType.String},?XPathResultType.String);
????????????????????break;
????????????}
????????????return?func;
????????}

?

2: XPathRegExExtensionFunction.cs

//?This?method?is?invoked?at?run?time?to?execute?the?user?defined?function.
????????public?object?Invoke(XsltContext?xsltContext,?object[]?args,
?????XPathNavigator?docContext)
????????{
????????????Regex?r;
????????????string?str?=?null;
????????????//?The?two?custom?XPath?extension?functions
????????????switch?(m_FunctionName)
????????????{
????????????????case?"Match":
????????????????????r?=?new?Regex(args[1].ToString());
????????????????????MatchCollection?m?=?r.Matches(args[0].ToString());
????????????????????if?(m.Count?==?0)
????????????????????{
????????????????????????return?false;
????????????????????}
????????????????????else
????????????????????{
????????????????????????return?true;
????????????????????}
????????????????????break;

????????????????case?"Split":
????????????????????r?=?new?Regex(args[1].ToString());
????????????????????string[]?s1?=?r.Split(args[0].ToString());
????????????????????int?n?=?Convert.ToInt32(args[2]);
????????????????????if?(s1.Length?<?n)
????????????????????????str?=?"";
????????????????????else
????????????????????????str?=?s1[n?-?1];
????????????????????break;
????????????????case?"Replace":
????????????????????r?=?new?Regex(args[1].ToString());
????????????????????string?s2?=?r.Replace(args[0].ToString(),?args[2].ToString());
????????????????????str?=?s2;
????????????????????break;
????????????}
????????????return?(object)str;
????????}

?

另外一個文件XPathExtensionVariable.cs其實和函數擴展沒有太多的關系，那是設置參數的。

這連個文件修改好了之后，就可以調用了：

query?=?navigator.Compile("xdUtil:Match(9,'\\d')");
????????????CustomContext?cntxt?=?new?CustomContext();
????????????//?Add?a?namespace?definition?for?myFunctions?prefix.
????????????cntxt.AddNamespace("xdUtil",?"http://myXPathExtensionFunctions");
????????????query.SetContext(cntxt);
????????????Evaluate(query,?navigator);

當然，要是支持XPath2.0 就好了，XPath2.0這些函數都是內置支持的，可惜目前好像還不支持。

全部的代碼在這里：
/Files/cleo/XPathExtFunction.rar

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