我有一些帶有默認名稱空間的xml<a xmlns='urn:test.Schema'><b/><b/></a>并想數 <b/>我該如何定義XmlNamespaceManager nsmgr = ????Assert.AreEqual(2, doc.SelectNodes("//b", nsmgr).Count);這樣斷言變為事實？到目前為止，我已經嘗試過（使用nunit）：[Test][Ignore("Why does this not work?")]public void __DoesNotWork_TestSelectWithDefaultNamespace(){    // xml to parse with defaultnamespace    string xml = @"<a xmlns='urn:test.Schema'><b/><b/></a>";    XmlDocument doc = new XmlDocument();    doc.LoadXml(xml);    // fails because xpath does not have the namespace    //!!!!    Assert.AreEqual(2, doc.SelectNodes("//b").Count);    // using XPath defaultnamespace     XmlNamespaceManager nsmgr = new XmlNamespaceManager(doc.NameTable);    nsmgr.AddNamespace("", "urn:test.Schema");    // This will fail with dotnet 3.5sp1. Why?    //!!!!    Assert.AreEqual(2, doc.SelectNodes("//b", nsmgr).Count);}[Test]public void TestSelectWithoutNamespaces_Ok(){    // xml to parse without namespace    string xml = @"<a><b/><b/></a>";    XmlDocument doc = new XmlDocument();    doc.LoadXml(xml);    // works ok    Assert.AreEqual(2, doc.SelectNodes("//b").Count);    // works ok    XmlNamespaceManager nsmgr = new XmlNamespaceManager(doc.NameTable);    Assert.AreEqual(2, doc.SelectNodes("//b", nsmgr).Count);}[Test]public void TestSelectWithNamespacesPrefixed_Ok(){    // xml to parse with defaultnamespace    string xml = @"<a xmlns='urn:test.Schema'><b/><b/></a>";    XmlDocument doc = new XmlDocument();    doc.LoadXml(xml);    // using XPath namespace via alias "t". works ok but xpath is to complicated    XmlNamespaceManager nsmgr = new XmlNamespaceManager(doc.NameTable);    nsmgr.AddNamespace("t", doc.DocumentElement.NamespaceURI);    Assert.AreEqual(2, doc.SelectNodes("//t:b", nsmgr).Count);}