XML 文档到 IEnumerable<XElement> 并获取值

Question

大家好，我正试图从我的 xdocument 中更深的容器中获取一些值，但我总是在 Nullreference 中运行。

这是我目前的代码：

                StreamReader xmlStream = new StreamReader(rsp.GetResponseStream());
            string XMLstr = xmlStream.ReadToEnd();
            XDocument xelement = XDocument.Parse(XMLstr);
            xmlStream.Close();


            IEnumerable<XElement> items = xelement.Elements();

            foreach (var item in items )
            {
                Console.WriteLine(item.Element("ItemID").Value.ToString());
            }

这是我要使用的 XML：

    <GetSellerListResponse xmlns="urn:ebay:apis:eBLBaseComponents">
  <Timestamp>2016-02-26T22:02:38.968Z</Timestamp>
  <Ack>Success</Ack>
  <Version>967</Version>
  <Build>967_CORE_BUNDLED_10708779_R1</Build>
  <PaginationResult>
    <TotalNumberOfPages>14</TotalNumberOfPages>
    <TotalNumberOfEntries>27</TotalNumberOfEntries>
  </PaginationResult>
  <HasMoreItems>true</HasMoreItems>
  <ItemArray>
    <Item>
      <AutoPay>false</AutoPay>
      <BuyerProtection>ItemIneligible</BuyerProtection>
      <Country>US</Country>
      <Currency>USD</Currency>
      <HitCounter>NoHitCounter</HitCounter>
      <ItemID>110043597553</ItemID>
      <ListingDetails>
        <StartTime>2016-02-12T23:35:27.000Z</StartTime>
        <EndTime>2016-02-19T23:35:27.000Z</EndTime>
        <ViewItemURL>http://cgi.sandbox.ebay.com/ws/eBayISAPI.dll?ViewItem&
           item=110043597553&category=41393</ViewItemURL>
        <HasUnansweredQuestions>false</HasUnansweredQuestions>
        <HasPublicMessages>false</HasPublicMessages>
        <BuyItNowAvailable>true</BuyItNowAvailable>
      </ListingDetails>
      <ListingDuration>Days_7</ListingDuration>
      <Location>Santa Cruz, California</Location>
      <PrimaryCategory>
        <CategoryID>41393</CategoryID>
        <CategoryName>Collectibles:Decorative Collectibles:Other</CategoryName>
      </PrimaryCategory>
      <Quantity>1</Quantity>
      <ReviseStatus>
        <ItemRevised>false</ItemRevised>
      </ReviseStatus>
      <SecondaryCategory>
        <CategoryID>95116</CategoryID>
        <CategoryName>Collectibles:Disneyana:Contemporary (1968-Now):Bobblehead Figures</CategoryName>
      </SecondaryCategory>
      <SellingStatus>
        <BidCount>0</BidCount>
        <BidIncrement currencyID="USD">0.5</BidIncrement>
        <ConvertedCurrentPrice currencyID="USD">11.49</ConvertedCurrentPrice>
        <CurrentPrice currencyID="USD">11.49</CurrentPrice>
        <MinimumToBid currencyID="USD">11.49</MinimumToBid>
        <QuantitySold>0</QuantitySold>
        <SecondChanceEligible>false</SecondChanceEligible>
        <ListingStatus>Completed</ListingStatus>
      </SellingStatus>
      <ShipToLocations>US</ShipToLocations>
      <Site>US</Site>
      <Storefront>
        <StoreCategoryID>1</StoreCategoryID>
        <StoreCategory2ID>0</StoreCategory2ID>
        <StoreURL>http://www.stores.sandbox.ebay.com/id=132854966</StoreURL>
      </Storefront>
      <SubTitle>Micky, with the ears!</SubTitle>
      <TimeLeft>PT0S</TimeLeft>
      <Title>Kelly's Kitsch</Title>
      <WatchCount>0</WatchCount>
      <PostalCode>95062</PostalCode>
      <PictureDetails>
        <GalleryURL>http://thumbs.ebaystatic.com/pict/41007087008080_0.jpg</GalleryURL>
        <PhotoDisplay>None</PhotoDisplay>
        <PictureURL>http://thumbs.ebaystatic.com/pict/41007087008080_0.jpg</PictureURL>
      </PictureDetails>
      <ProxyItem>false</ProxyItem>
      <ReturnPolicy>
        <RefundOption>MoneyBack</RefundOption>
        <Refund>Money Back</Refund>
        <ReturnsWithinOption>Days_30</ReturnsWithinOption>
        <ReturnsWithin>30 Days</ReturnsWithin>
        <ReturnsAcceptedOption>ReturnsAccepted</ReturnsAcceptedOption>
        <ReturnsAccepted>Returns Accepted</ReturnsAccepted>
        <Description>Returns accepted only if item is not as described.</Description>
        <ShippingCostPaidByOption>Buyer</ShippingCostPaidByOption>
        <ShippingCostPaidBy>Buyer</ShippingCostPaidBy>
      </ReturnPolicy>
      <PaymentAllowedSite>US</PaymentAllowedSite>
    </Item>
   </ItemArray>
  <ItemsPerPage>2</ItemsPerPage>
  <PageNumber>1</PageNumber>
  <ReturnedItemCountActual>2</ReturnedItemCountActual>
</GetSellerListResponse>

谁能解释一下我错过了什么？

谢谢

Answer 1

您在XDocument 上调用Elements()，所以这只是要返回根元素。

然后您在该根元素上调用 Element("ItemID") - 请求一个不存在的元素。所以这将返回null，导致您的异常。此外，您忽略了所有元素都在命名空间中这一事实。

看起来你可能真的想要 Item 元素，所以你可以使用：

// Changed the variable name to match what it is...
XDocument doc = XDocument.Parse(XMLstr);
XNamespace ns = "urn:ebay:apis:eBLBaseComponents";
Enumerable<XElement> items = doc.Descendants(ns + "Item");
foreach (var item in items)
{
    // XElement.Value is already a string; no need to call ToString on it
    Console.WriteLine(item.Element(ns + "ItemID").Value);
}

另一种方法是专门查找ItemArray 元素及其Item 子元素：

XDocument doc = XDocument.Parse(XMLstr);
XNamespace ns = "urn:ebay:apis:eBLBaseComponents";
Enumerable<XElement> items = doc.Root
                                .Element(ns + "ItemArray")
                                .Elements(ns + "Item");
// Code as before

Answer 2

致任何发现此内容的 VB 用户。首先要注意有一个命名空间，因此考虑到这一点的最简单方法之一是添加 Imports 语句。

Imports <xmlns="urn:ebay:apis:eBLBaseComponents">

接下来解析响应。

Dim someXE As XElement = XElement.Parse(XMLstr)

然后选择所有 ItemID，无论它们位于何处

Dim itemID As IEnumerable(Of XElement) = someXE...<ItemID>

最后再单独看看它们

For Each id As XElement In itemID
    Debug.WriteLine(id.Value) 'from example above 110043597553
Next