program that accepts an XML input string and get all node values by name from it.3

Question

This is my requirement: Write a program that accepts an XML input string and get all node values by name from it. Use the namespace System.XML ( Do not use System.XML.Linq).

Display & node values separated by space.

Example: If input string contains following string:

<Names> <Name> <FirstName>John</FirstName> <LastName>Smith</LastName</Name>
<Name><FirstName>James</FirstName> <LastName>White</LastName></Name></Names>

Display output as : John Smith James White

Create a class named UserProgramCode that has the following static method public static string getnodeByName(string input1) Create a class named Program that accepts the inputs and calls the static method present in the UserProgramCode.

And My code is

using System; using System.Xml;

public class Program{

    public static void Main(){

    string xmlinput=Console.ReadLine();
    UserProgramCode.getnodeByName(xmlinput);
    }

}

public class UserProgramCode{

    static string ResultName;
    public static string getnodeByName(string input1)
    {

        XmlDocument xmlDoc = new XmlDocument();
        xmlDoc.LoadXml(input1);
        string xpath ="Names/Name";
        var nodes = xmlDoc.SelectNodes(xpath);
        foreach (XmlNode childrenNode in nodes)
        {
              UserProgramCode.ResultName=childrenNode.SelectSingleNode("/FirstName").InnerText +" "+ childrenNode.SelectSingleNode("/LastName").InnerText;
        }
        return UserProgramCode.ResultName;
    }
}

But I am getting Null reference Exception.I have no idea how to resolve this. Please help . I am new to C#.net.

John Smith James White Unhandled Exception: System.NullReferenceException: Object reference not set to an instance of an object at UserProgramCode.getnodeByName (System.String input1) [0x00000] in :0 at Program.Main () [0x00000] in :0 [ERROR] FATAL UNHANDLED EXCEPTION: System.NullReferenceException: Object reference not set to an instance of an object at UserProgramCode.getnodeByName (System.String input1) [0x00000] in :0 at Program.Main () [0x00000] in :0

I'm guessing the null reference exception is because `SelectSingleNode( )` is returning null, and if it does, trying to access `.InnerText` will cause this error. You can prevent it from crashing your program if you use `?.InnerText`, but in your case you need to figure out why `SelectSingleNode()` is returning null. Hint: `/` at the beginning of an XPath behaves similarly to how it does with a filesystem path. — Dylan Nicholson, Dec 03 '17 at 08:43
There are two issues : 1) You are missing a '>' after last name. 2) You need a period in the path : UserProgramCode.ResultName = childrenNode.SelectSingleNode("./FirstName").InnerText + " " + childrenNode.SelectSingleNode("./LastName").InnerText; — jdweng, Dec 03 '17 at 10:07
Possible duplicate of [What is a NullReferenceException, and how do I fix it?](https://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-and-how-do-i-fix-it) — Progman, Dec 03 '17 at 13:01

score 1 · Accepted Answer · answered Dec 04 '17 at 02:32

I see multiple problems here:

Your Input XML is malformed. You should try catch while LoadXml as a user can enter anything to break your code. Smith</LastName ">" is missing.
/ in front of the nodes name /FirstName will make it start search from the root of the current node.
Assigning to ResultName will only keep last node's First and Last Name and discard all others.
Using a string concatenation will result in wasted heap.
Naming conventions don't match C# standards.

Updated sample:

    public class UserProgramCode
    {
     static StringBuilder resultName = new StringBuilder();
     public static string GetNodeByName(string input1)
     {
        XmlDocument xmlDoc = new XmlDocument();
        try
        {
            xmlDoc.LoadXml(input1);
        }
        catch (XmlException xe)
        {
            Console.WriteLine("Input XML is not parseable. " + xe.Message);
        }
        string xpath = "Names/Name";
        var nodes = xmlDoc.SelectNodes(xpath);
        foreach (XmlNode childrenNode in nodes)
        {
            resultName.AppendLine(childrenNode.SelectSingleNode("FirstName").InnerText + " " + childrenNode.SelectSingleNode("LastName").InnerText);
        }
        return resultName.ToString();
     }
    }

program that accepts an XML input string and get all node values by name from it.3

1 Answers1