Question

我试图编写一个C＃应用程序，该应用程序解析XML文件并通过函数返回选定的节点。这些是我的课程：

XmlDocumentParser.cs

using System;
using System.Text;
using System.IO;
using System.Xml;

namespace Namespace1
{
    public class XmlDocumentParser
    {
        // This is a private instance variable that cannot be reassigned
        private readonly XmlDocument document = new XmlDocument();
        private string udc = "urn:rosettanet:specification:universal:Document:xsd:schema:01.12";
        private string udct = "urn:rosettanet:specification:universal:DocumentType:xsd:codelist:01.13";
        private string tns = "urn:rosettanet:specification:interchange:PurchaseOrderRequest:xsd:schema:02.05";
        private string dp = "urn:rosettanet:specification:domain:Procurement:xsd:schema:02.29";

        //This is the constructor
        public XmlDocumentParser(string documentPath)
        {
            document.Load(documentPath);
            XmlNode Root = document.DocumentElement;
            XmlNamespaceManager Nsmgr = new XmlNamespaceManager(document.NameTable);
            Nsmgr.AddNamespace("udc", udc); 
            Nsmgr.AddNamespace("udct", udct);
            Nsmgr.AddNamespace("tns", tns);
        }

        // This is a public property that can only be read and not set
        public XmlNode Root { private set; get; }
        public XmlNode Nsmgr {private set; get; }
    }
}

PORReader.cs

using System;
using System.Text;
using System.IO;
using System.Xml;


namespace Namespace1 {
    public class PORReader {
    private readonly XmlNode root;
    private readonly XmlNamespaceManager nsmgr;
    public PORReader(string documentPath){ 
        var xmlDocumentParser = new XmlDocumentParser(documentPath);
        var root = xmlDocumentParser.Root;  
    }

    public object getPurchaseOrder(){

        XmlNode node = root.SelectSingleNode(
                "descendant::tns:PurchaseOrder/udc:BusinessDocumentReference[udct:DocumentType='SAO']/udc:Identifier", nsmgr);
        return returnNode(node.InnerXml);
    }

        private object returnNode(object node){
            if (node != null) {
                return node;
            } else {
                return "Error in Node";
            }
        }
    }
}

Program.cs：

using System;
using System.Text;
using System.IO;
using System.Xml;

namespace Namespace1
{
    class Program
    {        
        static void Main(string[] args){
            // This will reside in the reader classes
            var xmlDocumentParser = new XmlDocumentParser("/Users/moorel/Desktop/Projects/C#/O2/DummyFiles/SupplyChainSourceFiles/POR/POR_SALES_8307_20180201164154.xml");
            var root = xmlDocumentParser.Root;
            var nsmgr = xmlDocumentParser.Nsmgr;
        }
    }
}

我的测试是：

namespace Namespace1 {
    using NUnit.Framework;

    [TestFixture]
    public class PORReaderTest {
        [Test]
        public void getPurchaseOrder(){

            PORReader reader = new PORReader("/Users/moorel/Desktop/Projects/C#/O2/DummyFiles/SupplyChainSourceFiles/POR/POR_SALES_8307_20180201164154.xml");
            Assert.AreEqual(reader.getPurchaseOrder(), "aa036E31tc63qjPfIMJ");
        }
    }
}

因此，xml的文档路径是正确的，并且xml中存在值“ aaaaE31tc63qjPfIMJ”，但是测试出现错误，消息为System.NullReferenceException : Object reference not set to an instance of an object.

在类PORReader中，root的值为null，我需要它成为从XmlDocumentParser导入的对象。我不熟悉C＃类，因此不胜感激

谢谢！

Answer 1

我知道了。

您不会在XmlDocumentParser构造函数中执行任何操作。

此行：

XmlNode Root = document.DocumentElement;

不分配给Root属性，它创建一个名为Root的局部变量。更改为

Root = document.DocumentElement;

，看看是否有帮助。同样，使用调试器运行并查看一切是否正确，例如如果document.DocumentElement实际上返回了您要查找的根。

编辑：

我是盲人。

您在PORReader中有完全相同的错误。

var root = xmlDocumentParser.Root;

这不会分配给您的private readonly字段，而是创建一个局部变量。更改为：

root = xmlDocumentParser.Root;

Answer 2

XmlDocumentParser.cs

namespace Namespace1
{
    public class XmlDocumentParser
    {
        // This is a private instance variable that cannot be reassigned
        private readonly XmlDocument document = new XmlDocument();
        private string udc = "urn:rosettanet:specification:universal:Document:xsd:schema:01.12";
        private string udct = "urn:rosettanet:specification:universal:DocumentType:xsd:codelist:01.13";
        private string tns = "urn:rosettanet:specification:interchange:PurchaseOrderRequest:xsd:schema:02.05";
        private string dp = "urn:rosettanet:specification:domain:Procurement:xsd:schema:02.29";

        //This is the constructor
        public XmlDocumentParser(string documentPath)
        {
            document.Load(documentPath);
            Root = document.DocumentElement as XmlNode;
            Nsmgr = new XmlNamespaceManager(document.NameTable);
            Nsmgr.AddNamespace("udc", udc);
            Nsmgr.AddNamespace("udct", udct);
            Nsmgr.AddNamespace("tns", tns);
        }

        // This is a public property that can only be read and not set
        public XmlNode Root { get; }
        public XmlNamespaceManager Nsmgr { get; }
    }
}

类之间的C＃传递对象为null

2 个答案: