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XML現有元素nullReferenceExceptionUnhandled錯誤試圖解析這個XML我不斷地得到在這一點上的100個變化我雖然我更好地做一個職位之前,我開始摔東西(如我的顯示器)上解析使用的XDocument
System.NullReferenceException was unhandled
HResult=-2147467261
Message=Object reference not set to an instance of an object.
Source=
StackTrace:
at Dashboard.Global.geocoder(Object o) in :line 60
at System.Threading.TimerQueueTimer.CallCallbackInContext(Object state)
at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.TimerQueueTimer.CallCallback()
at System.Threading.TimerQueueTimer.Fire()
at System.Threading.TimerQueue.FireNextTimers()
at System.Threading.TimerQueue.AppDomainTimerCallback()
InnerException:
該XML是FCC.gov很簡單
<Response xmlns="http://data.fcc.gov/api" status="OK" executionTime="91">
<Block FIPS="181770103002004"/>
<County FIPS="18177" name="Wayne"/>
<State FIPS="18" code="IN" name="Indiana"/>
</Response>
我的代碼已經演變頗有幾分
var xdoc = XDocument.Load(response.GetResponseStream());
XNamespace ns = xdoc.Root.Attribute("xmlns").ToString();
var results = xdoc.Element(ns + "Response").Element(ns + "Block").Attribute("FIPS"); //null ref
if (xdoc != null)
{
var FIPS_State_Code = results.Value.Substring(0,1); //null ref
var FIPS_County_Code = xdoc.Element("response"); //nullref
var Census_Tract = xdoc.Element("response").Element("Block").Attribute("FIPS").Value; //null ref
var Census_Block_Group = xdoc.Element("response").Element("Block"); //null ref
通過tomolak最終產品已回答(如果你確實拉普查塊):
var xdoc = XDocument.Load(response.GetResponseStream());
XNamespace fcc = "http://data.fcc.gov/api";
var results = xdoc.Element(fcc + "Response").Element(fcc + "Block").Attribute("FIPS").Value.ToString();
if (xdoc != null)
{
var FIPS_State_Code = results.Substring(0,2);
var FIPS_County_Code = results.Substring(2, 3);
var Census_Tract = results.Substring(5, 6);
var Census_Block_Group = results.Substring(11, 4);
}
注意,一個良好的避免LINQ to XML中的空引用異常的方法是對'string'做一個明確的轉換 - 即'var FIPS_Block_Code =(string)block.Attribute(「FIPS」); - 如果找不到屬性,它將返回空值。在這種情況下不太可能出現這種情況,但這是一種很好的最佳做法,尤其是當您無法一直指望存在的元素/屬性時。 – Tim
這完美的作品!我知道它必須是命名空間,但我不能正確地得到它 – Vinez
謝謝蒂姆我會記住這一點 – Vinez