使用xpath選擇元素值

Question

鑑於此XML，如何使用xpath查詢選擇PostBack的值？

<AuthenticateResponse xmlns="http://example.com/authentication/response/1"> 
    <Status>success</Status> 
    <Result>more-info</Result> 
    <StateContext /> 
    <AuthenticationRequirements> 
    <PostBack>/Authentication/ExplicitForms/AuthenticateAttempt</PostBack> 
    <CancelPostBack>/Authentication/ExplicitForms/CancelAuthenticate</CancelPostBack> 
    <CancelButtonText>Cancel</CancelButtonText> 
    </AuthenticationRequirements> 
</AuthenticateResponse> 

我希望這個工作，但它返回null：

var nsmgr = new XmlNamespaceManager(doc.NameTable); 
nsmgr.AddNamespace("AuthenticateResponse", "http://example.com/authentication/response/1"); 
var node = doc.SelectSingleNode("//AuthenticateResponse:AuthenticationRequirements/PostBack", nsmgr); 

Answer 1

你應該指定你的XPath都在提的每個元素的命名空間：

var nsmgr = new XmlNamespaceManager(doc.NameTable); 
nsmgr.AddNamespace("ns", "http://example.com/authentication/response/1"); 
var xpath = "/ns:AuthenticateResponse/ns:AuthenticationRequirements/ns:PostBack"; 
var node = doc.SelectSingleNode(xpath, nsmgr); 

Answer 2

它應該是：

var node = doc.SelectSingleNode("/AuthenticateResponse:AuthenticateResponse/AuthenticateResponse:AuthenticationRequirements/AuthenticateResponse:PostBack", nsmgr);