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：
http://cleo.VEVb.com/Files/cleo/XPathExtFunction.rar

出處：cleo BLOG