Reading multiple XML attributes

Question

I'm trying to get information from XML library (file below) using C# in Visual Studio.

<buttons>
<measurement>
    <scan id="0" time="20 53 06">
        <q address="40" state="0"/>
        <q address="41" state="0"/>
        <q address="42" state="1"/>
        <q address="43" state="0"/>
        <q address="44" state="1"/>
        <q address="45" state="1"/>
        <q address="46" state="1"/>
        <q address="47" state="1"/>
    </scan>
</measurement>
<measurement>
    <scan id="1" time="20 53 07">
        <q address="40" state="0"/>
        <q address="41" state="0"/>
        <q address="42" state="0"/>
        <q address="43" state="0"/>
        <q address="44" state="1"/>
        <q address="45" state="0"/>
        <q address="46" state="0"/>
        <q address="47" state="0"/>
    </scan>
</measurement>
<measurement>
    <scan id="2" time="20 53 08">
        <q address="40" state="0"/>
        <q address="41" state="1"/>
        <q address="42" state="0"/>
        <q address="43" state="1"/>
        <q address="44" state="1"/>
        <q address="45" state="0"/>
        <q address="46" state="0"/>
        <q address="47" state="1"/>
    </scan>
</measurement>
<measurement>
    <scan id="3" time="20 53 09">
        <q address="40" state="1"/>
        <q address="41" state="0"/>
        <q address="42" state="0"/>
        <q address="43" state="1"/>
        <q address="44" state="1"/>
        <q address="45" state="0"/>
        <q address="46" state="1"/>
        <q address="47" state="0"/>
    </scan>
</measurement>
<measurement>
    <scan id="4" time="20 53 10">
        <q address="40" state="0"/>
        <q address="41" state="0"/>
        <q address="42" state="1"/>
        <q address="43" state="1"/>
        <q address="44" state="1"/>
        <q address="45" state="1"/>
        <q address="46" state="0"/>
        <q address="47" state="0"/>
    </scan>
</measurement>
<measurement>
    <scan id="5" time="20 53 11">
        <q address="40" state="1"/>
        <q address="41" state="1"/>
        <q address="42" state="1"/>
        <q address="43" state="0"/>
        <q address="44" state="0"/>
        <q address="45" state="0"/>
        <q address="46" state="1"/>
        <q address="47" state="0"/>
    </scan>
</measurement>
<measurement>
    <scan id="6" time="20 53 12">
        <q address="40" state="0"/>
        <q address="41" state="1"/>
        <q address="42" state="1"/>
        <q address="43" state="0"/>
        <q address="44" state="0"/>
        <q address="45" state="1"/>
        <q address="46" state="1"/>
        <q address="47" state="1"/>
    </scan>
</measurement>
<measurement>
    <scan id="7" time="20 53 13">
        <q address="40" state="1"/>
        <q address="41" state="1"/>
        <q address="42" state="1"/>
        <q address="43" state="1"/>
        <q address="44" state="1"/>
        <q address="45" state="0"/>
        <q address="46" state="1"/>
        <q address="47" state="1"/>
    </scan>
</measurement>

it is my first attempt to do and read xml files.

Hre is what i want to do:
I want to inpud ID and program schould return all q states in array.

Here is what I tried:

using System.Xml;
XmlDocument xmlDoc = new XmlDocument();
xmlDoc.Load("Path to my xml");
XmlNodeList titleNodes = xmlDoc.SelectNodes("//buttons/measurment/scan/q");
foreach(XmlNode titleNode in titleNodes)
    Console.WriteLine(titleNode.Attribute["address"]);
Console.ReadKey();

I know that this code will only display some q atributes in console. I never went furder because it is not working (nothing appears in console window) . And i dont know why. I just don understand this XmlRead, XmlDeocument. I was learnig form here: Tutorial. I was folowing every stem and examlpes. Only XmlRead giave something to me. Bu it reads just everything, not specific regions.

Can you show me some examples or solutions?

I'm not looking into this too much, but your SelectNodes has the wrong casing - Try changing the upper case "Q" - "//buttons/measurment/scan/q" — John Bustos
– John Bustos, Commented Aug 23, 2016 at 12:50
you input the scan id, and get all the q states? is that what you're asking — Jonesopolis
– Jonesopolis, Commented Aug 23, 2016 at 12:54
All q states from specific scan area. For examle tag scan has atribute id="0" and i wan all q states from this tag area. — MrJW
– MrJW, Commented Aug 23, 2016 at 12:56
What you want to do is something like this: SelectNodes("//scan[contains(id,""'YOURSELECTEDID'"")]") — Marcel Theis
– Marcel Theis, Commented Aug 23, 2016 at 12:58

Jonesopolis · Accepted Answer · 2016-08-23 13:28:37Z

3

Consider using XDocument, which allows you to use LINQ, making your xml life easier:

string myId = "2";

var doc = XDocument.Parse(xmlString); //or XDocument.Load(filePath)

//find the correct 'scan' node based on your id
var scan = doc.Descendants("scan")
              .FirstOrDefault(s => s.Attribute("id").Value == myId);

//grab all q's and get their 'state' for that 'scan' node
var states = scan?.Descendants("q")
                  .Select(q => q.Attribute("state").Value);

foreach (var state in states)
{
    Console.WriteLine(state);
}

edited Aug 23, 2016 at 13:28

answered Aug 23, 2016 at 12:58

Jonesopolis

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6 Comments

user6996876 Over a year ago

If the scan is null (when the id is not found), you'll get a NullReferenceException in the foreach... so ?. only puts it off to the next instruction

user6996876 Over a year ago

I'd suggest a var states = scan?.Descendants("q").Select(q => q.Attribute("state").Value) ?? Enumerable.Empty <string>(); :-) but of course there are thousand ways...

MrJW Over a year ago

This solution looks good, but VisualStudio don't recodnise XDocument. And yes I added System.Linq library.

user6996876 Over a year ago

@MrJW the namespace for XDocument is System.Xml.Linq and minimum .Net Framework is 3.5 (Visual Studio 2008)

MrJW Over a year ago

I typed file path, for example "XDocument.Parse(/data/test.xml)" file test.xml containt data described in my main post. I also added library System.Xml.Linq but when I run application, excepion unhandle apperars: "An unhandled exception of type 'System.Xml.XmlException' occurred in System.Xml.dll Additional information: Data at the root level is invalid. Line 1, position 1. "

|

score 1 · Accepted Answer · 2016-08-23 15:30:47Z

1

Assuming the xml is well formed and the root node is corectly closed, you have a typo in the string measurement and this is correctly selecting all the q tags

XmlNodeList titleNodes = xmlDoc.SelectNodes("//buttons/measurement/scan/q");

If you want only the ones under one id

XmlNodeList titleNodes = xmlDoc.SelectNodes("//buttons/measurement/scan[@id=2]/q") ;

If there is no such id, you'll get an empty collection but not an exception error: so that case is managed.

Finally, don't forget the Value field

Console.WriteLine(titleNode.Attributes["address"].Value);

edited Aug 23, 2016 at 15:30

answered Aug 23, 2016 at 13:25

user6996876

2 Comments

MrJW Over a year ago

Your solution looks the best, but (i don't know why) Attributes are not recognised. I just get red line under this word. And sorry for typos. I'm not a native english speaker,I translated my code so it is more redable here.

MrJW Over a year ago

After some tweaking everything works( my part of the code, your is perfect :) ). Thanks, you helped me alot :)

vemund · Accepted Answer · 2016-08-23 13:09:41Z

0

XmlNodeList titleNodes = xmlDoc.SelectNodes("//measurement/scan/q");

Then you will get 64 items back.

answered Aug 23, 2016 at 13:09

vemund

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