c# - 如何从网络服务获取输入

Question

我正在尝试编写一个程序，该程序将从网络服务接收输入并选择与订单 ID 一起的正确信息。我使用 xPath 来实现这一点，因为它是必需的。例如，如果我在运行程序时在 OrderID 下输入 1，它应该提取该订单的总成本并显示它。我知道我的代码肯定有问题，因为我是新手，所以当我无法控制所使用的变量时，我不知道如何物理获取输入。任何帮助将不胜感激，谢谢!

这是我的代码:

[WebMethod]
public int GetTotalCostForAnOrder(int OrderID)
{
    XPathNavigator nav;
    XPathDocument docNav;
    XPathNodeIterator NodeIter;

    String rootPath = Server.MapPath("~");
    string strFilename = rootPath + "\\OrderInfoLab3.xml";
    docNav = new XPathDocument(strFilename);

    // Create a navigator to query with XPath.
    nav = docNav.CreateNavigator();
    String searchString = "sum(OrderFeed/Order/Items/Item/TotalCost)";

    // you need to determine the proper XPath statement

    // Select the node and place the results in an iterator.
    NodeIter = nav.Select(searchString);

    while (NodeIter.MoveNext())
    {
        NodeIter.Current.Select("OrderID");
    }

    var totalOrder = nav.Compile(searchString);
    return Convert.ToInt32(nav.Evaluate(totalOrder));
}

这是我的 XML 文件:

<Order id="1">
<BillingInformation>
    <Name>Bruce Ganek</Name>
    <Address>99 Main Street</Address>
    <City>Cranston</City>
    <State>RI</State>
    <ZipCode>02910</ZipCode>
</BillingInformation>
<ShippingInformation>
    <Name>Governor Chafee</Name>
    <Address>82 Smith St # 115</Address>
    <City>Providence</City>
    <State>RI</State>
    <ZipCode>02903-1121</ZipCode>
</ShippingInformation>
<Items>
    <Item>
        <PartNo>JETSWEATER</PartNo>
        <Description>N.Y. Jets Sweatshirt</Description>
        <UnitPrice>10.50</UnitPrice>
        <Quantity>2</Quantity>
        <TotalCost>21.00</TotalCost>
        <CustomerOptions>
            <Size>M</Size>
            <Color>Green</Color>
        </CustomerOptions>
    </Item>
    <Item>
        <PartNo>JETSWEATER</PartNo>
        <Description>N.Y. Jets Sweatshirt</Description>
        <UnitPrice>7.50</UnitPrice>
        <Quantity>3</Quantity>
        <TotalCost>22.50</TotalCost>

        <CustomerOptions>
            <Size>S</Size>
            <Color>White</Color>
        </CustomerOptions>
    </Item>
    <Item>
        <PartNo>JETSFLASHLIGHT</PartNo>
        <Description>N.Y. Jets Flashlight</Description>
        <UnitPrice>5.00</UnitPrice>
        <Quantity>1</Quantity>
        <TotalCost>5.00</TotalCost>

        <CustomerOptions/>

    </Item>

</Items>
</Order>

这是我在输出中遇到的错误:

System.Xml.XPath.XPathException: Expression must evaluate to a node-set.
at System.Xml.XPath.XPathNavigator.Select(XPathExpression expr)
at System.Xml.XPath.XPathNavigator.Select(String xpath)
at Lab3.Service1.GetTotalCostForAnOrder(Int32 OrderID) in C:\

Answer 1

以下行似乎不正确:

String searchString = "sum(OrderFeed/Order/Items/Item/TotalCost)";

这应该是选择节点的 XPath 表达式，但 XML 中没有 OrderFeed 节点 - 根节点是 Order。

作为节点集合，这应该会带来更好的结果:

String searchString = "/Order/Items/Item/TotalCost";