I'm trying to obtain the relevant XML attribute based on the value but I cannot get it to work.
What I am trying to achieve is based on the returned value I want to output the elements name.
Where am I going wrong?
Here's my code so far:
XML:
<addresses>
<address name="house 1">No 1</ipaddress>
<address name="house 2">Flat 3</ipaddress>
<address name="house 3">Siccamore Drive</ipaddress>
</addresses>
C#:
string configPath = _AppPath + #"\HouseAddresses.xml";
XDocument addressXdoc = XDocument.Load(configPath);
XElement addressXmlList = addressXdoc.Element("traplistener");
foreach (XNode node in addressXmlLst.Element("addresses").Descendants())
{
PropertyList = ("string")node.Attribute("name");
}
The XNode type can be seen as a "base". As the documentation states, it represents the abstract concept of a node (element, comment, document type, processing instruction, or text node) in the XML tree. Adding a Attribute property to a text, for example, does not really make sense in the XML context. For that reason, the XNode type does not provide a Attribute property. The XElement type, however, does. Therefore, changing your foreach loop to the version bellow, should do the trick:
foreach (XElement element in addressXmlLst.Element("addresses").Descendants())
{
PropertyList = ("string")element.Attribute("name");
}
A "random" note on your code: since XElement extends XNode the elements returned by Descendants() are correctly converted; for this reason, your problem appears to come from the fact that XNode does not expose a Attribute property, when, in fact, it originates from an unnecessary type conversion.
As an improvement, I would suggest the following:
foreach (XElement element in addressXmlLst.Element("addresses").Descendants())
{
//check if the attribute is really there
//in order to prevent a "NullPointerException"
if (element.Attribute("name") != null)
{
PropertyList = element.Attribute("name").Value;
}
}
In addition to Andrei's answer you can also convert the xml to a dictionary directly via LINQ:
var dictionary = addressXmlLst.Element("addresses").Descendants()
.ToDictionary(
element => element.Attribute("name").Value, // the key
element => element.Value // the value
);
Related
Given the following XML:
<enrollment>
<school>
<students>
<studentA fname="John" lname="Doe" age="23" />
<studentB fname="Mary" lname="Johnson" age="22" />
</students>
</school>
</enrollment>
and here's my code to iterate the attributes-
foreach(XmlAttribute attr in node.Attributes)
{
//--get the XPath for each attribute
}
Where node = "studentA", how do I get the XPath for each attribute?
EDIT:
Basically what I'm trying to achieve here is to compare if two nodes are the same. So I have to check if they have the same name, attributes, and attribute values. Therefore given a node, I need an xpath expression that that matches the conditions stated.
you can directly put it like as for all the studentA nodes-
Xpath- "//studentA"
or to iterate over a specific node-
Xpath- "enrollment/school/students/studentA"
In case you want to find attribute fname
Xpath- "enrollment/school/students/studentA[#fname]"
Assuming myXml is your xmlDocument
you can iterate over a particular node attributes like-
System.Xml.XmlNode xn = myXml.SelectSingleNode("enrollment/school/students/studentA");
foreach (System.Xml.XmlAttribute attrib in xn.Attributes)
{
// find attribute name using attrib.Name
string sAttribName = attrib.Name;
if (sAttribName == "fname")
{
//Check your codes here
}
}
You can use enrollment/school/students/studentA/#fname
#attribute is for attribute selection.
I'm trying to traverse an XML document and select certain node attributes. The XML is dynamically generated.
<?xml version="1.0" encoding="ISO-8859-1"?>
<streams>
<stream>
<title>+23 (Panama)</title>
<info resolution="768x420" bitrate="1000kbps"/> ----- Need These
<swfUrl>http://www.freeetv.com/script/mediaplayer/player.swf</swfUrl>
<link>rtmp://200.75.216.156/live/</link>
<pageUrl>http://www.freeetv.com/</pageUrl>
<playpath>livestream</playpath>
<language>Music</language>
<advanced></advanced>
</stream>
</streams>
The code that I'm trying to use with zero luck and Visual Studio saying "No you're wrong. Try 600 more times" is
xDoc.Load("http://127.0.0.1/www/xml.php");
XmlNodeList nodes = xDoc.SelectNodes("/streams/stream");
foreach (XmlNode xn in nodes)
{
ListViewItem lvi = listView1.Items.Add(xn["title"].InnerText);
lvi.SubItems.Add(xn["swfUrl"].InnerText);
lvi.SubItems.Add(xn["link"].InnerText);
lvi.SubItems.Add(xn["pageUrl"].InnerText);
lvi.SubItems.Add(xn["playpath"].InnerText);
lvi.SubItems.Add(xn["language"].InnerText);
lvi.SubItems.Add(xn["advanced"].InnerText);
lvi.SubItems.Add(xn["//info/#resolution"].Value);
}
Please tell me oh wise ones what am I doing wrong?
If you want to select node's attribute using XPath you should use SelectSingleNode method, e.g.:
xn.SelectSingleNode("info/#resolution").Value
To select resolution attribute of your last node you need to use:
xn["info"].Attributes["resolution"].Value
Alternatively, you can try LINQ to XML for the same results (I find its API easier to use):
var doc = XDocument.Parse("http://127.0.0.1/www/xml.php");
foreach (var d in doc.Descendants("stream"))
{
ListViewItem lvi = listView1.Items.Add(d.Element("title").Value);
lvi.SubItems.Add(d.Element("swfUrl").Value);
// ...
vi.SubItems.Add(d.Element("info").Attribute("resolution").Value);
}
Here is an example of LINQ to XML to extract attributes from the entire document of a particular attribute name OR list of attribute names.
var xml = XElement.Parse("http://127.0.0.1/www/xml.php");
// find all attributes of a given name
var attributes = xml
.Descendants()
.Attributes("AttributeName")
// find all attributes of multiple names
var attributes = xml
.Descendants()
.Attributes()
.Where(a => ListOfAttribNames.Contains(a.Name.LocalName))
Replace:
lvi.SubItems.Add(xn["//info/#resolution"].Value);
with:
lvi.SubItems.Add(xn.SelectSingleNode("info/#resolution").Value);
I have a simple XML
<AllBands>
<Band>
<Beatles ID="1234" started="1962">greatest Band<![CDATA[lalala]]></Beatles>
<Last>1</Last>
<Salary>2</Salary>
</Band>
<Band>
<Doors ID="222" started="1968">regular Band<![CDATA[lalala]]></Doors>
<Last>1</Last>
<Salary>2</Salary>
</Band>
</AllBands>
However ,
when I want to reach the "Doors band" and to change its ID :
using (var stream = new StringReader(result))
{
XDocument xmlFile = XDocument.Load(stream);
var query = from c in xmlFile.Elements("Band")
select c;
...
query has no results
But
If I write xmlFile.Elements().Elements("Band") so it Does find it.
What is the problem ?
Is the full path from the Root needed ?
And if so , Why did it work without specify AllBands ?
Does the XDocument Navigation require me to know the full level structure down to the required element ?
Elements() will only check direct children - which in the first case is the root element, in the second case children of the root element, hence you get a match in the second case. If you just want any matching descendant use Descendants() instead:
var query = from c in xmlFile.Descendants("Band") select c;
Also I would suggest you re-structure your Xml: The band name should be an attribute or element value, not the element name itself - this makes querying (and schema validation for that matter) much harder, i.e. something like this:
<Band>
<BandProperties Name ="Doors" ID="222" started="1968" />
<Description>regular Band<![CDATA[lalala]]></Description>
<Last>1</Last>
<Salary>2</Salary>
</Band>
You can do it this way:
xml.Descendants().SingleOrDefault(p => p.Name.LocalName == "Name of the node to find")
where xml is a XDocument.
Be aware that the property Name returns an object that has a LocalName and a Namespace. That's why you have to use Name.LocalName if you want to compare by name.
You should use Root to refer to the root element:
xmlFile.Root.Elements("Band")
If you want to find elements anywhere in the document use Descendants instead:
xmlFile.Descendants("Band")
The problem is that Elements only takes the direct child elements of whatever you call it on. If you want all descendants, use the Descendants method:
var query = from c in xmlFile.Descendants("Band")
My experience when working with large & complicated XML files is that sometimes neither Elements nor Descendants seem to work in retrieving a specific Element (and I still do not know why).
In such cases, I found that a much safer option is to manually search for the Element, as described by the following MSDN post:
https://social.msdn.microsoft.com/Forums/vstudio/en-US/3d457c3b-292c-49e1-9fd4-9b6a950f9010/how-to-get-tag-name-of-xml-by-using-xdocument?forum=csharpgeneral
In short, you can create a GetElement function:
private XElement GetElement(XDocument doc,string elementName)
{
foreach (XNode node in doc.DescendantNodes())
{
if (node is XElement)
{
XElement element = (XElement)node;
if (element.Name.LocalName.Equals(elementName))
return element;
}
}
return null;
}
Which you can then call like this:
XElement element = GetElement(doc,"Band");
Note that this will return null if no matching element is found.
The Elements() method returns an IEnumerable<XElement> containing all child elements of the current node. For an XDocument, that collection only contains the Root element. Therefore the following is required:
var query = from c in xmlFile.Root.Elements("Band")
select c;
Sebastian's answer was the only answer that worked for me while examining a xaml document. If, like me, you'd like a list of all the elements then the method would look a lot like Sebastian's answer above but just returning a list...
private static List<XElement> GetElements(XDocument doc, string elementName)
{
List<XElement> elements = new List<XElement>();
foreach (XNode node in doc.DescendantNodes())
{
if (node is XElement)
{
XElement element = (XElement)node;
if (element.Name.LocalName.Equals(elementName))
elements.Add(element);
}
}
return elements;
}
Call it thus:
var elements = GetElements(xamlFile, "Band");
or in the case of my xaml doc where I wanted all the TextBlocks, call it thus:
var elements = GetElements(xamlFile, "TextBlock");
How to get a value of XElement without getting child elements?
An example:
<?xml version="1.0" ?>
<someNode>
someValue
<child>1</child>
<child>2</child>
</someNode>
If i use XElement.Value for <someNode> I get "somevalue<child>1</child><child>2<child>" string but I want to get only "somevalue" without "<child>1</child><child>2<child>" substring.
You can do it slightly more simply than using Descendants - the Nodes method only returns the direct child nodes:
XElement element = XElement.Parse(
#"<someNode>somevalue<child>1</child><child>2</child></someNode>");
var firstTextValue = element.Nodes().OfType<XText>().First().Value;
Note that this will work even in the case where the child elements came before the text node, like this:
XElement element = XElement.Parse(
#"<someNode><child>1</child><child>2</child>some value</someNode>");
var firstTextValue = element.Nodes().OfType<XText>().First().Value;
There is no direct way. You'll have to iterate and select. For instance:
var doc = XDocument.Parse(
#"<someNode>somevalue<child>1</child><child>2</child></someNode>");
var textNodes = from node in doc.DescendantNodes()
where node is XText
select (XText)node;
foreach (var textNode in textNodes)
{
Console.WriteLine(textNode.Value);
}
I think what you want would be the first descendant node, so something like:
var value = XElement.Descendents.First().Value;
Where XElement is the element representing your <someNode> element.
You can specifically ask for the first text element (which is "somevalue"), so you could also do:
var value = XElement.Descendents.OfType<XText>().First().Value;
I'm new to C#, and just started using XmlElement and its SelectSingleNode method. In my XML file there's a tag that may have a value (i.e. <tag>value</tag>) or be empty (i.e. <tag></tag>). If it's empty, SelectSingleNode returns null.
I'm currently using the following code to catch the value of the tag:
XmlElement elem = ....
string s = elem.SelectSingleNode("somepath").Value;
This code obviously raises an exception for empty tags. However, for me an empty tag is a valid value, where I expect the value of my string to be "".
Wrapping each call to SelectSingleNode with try...catch seems a huge waste of code (I have many fields that may be empty), and I'm sure there's a better way to achieve this.
What is the recommended approach?
EDIT:
Following requests, a sample XML code will be:
<Elements>
<Element>
<Name>Value</Name>
<Type>Value</Type> <-- may be empty
<Color>Value</Color>
</Element>
<Element>
<Name>Value</Name>
<Type>Value</Type>
<Color>Value</Color>
</Element>
</Elements>
The CS code:
XmlDocument doc = new XmlDocument();
doc.Load("name.xml");
foreach (XmlElement elem in doc.SelectNodes("Elements/Element"))
{
myvalue = elem.SelectSingleNode("Type/text()").Value;
}
Your sample code:
myvalue = elem.SelectSingleNode("Type/text()").Value;
is where the problem is. The XPath expression you've used there doesn't mean "give me text of element Type". It means "give me all child text nodes of element Type". And an empty element doesn't have any child text nodes (a text node cannot be empty in XPath document model). If you want to get text value of the node, you should use:
myvalue = elem.SelectSingleNode("Type").InnerText;
The recommended approach would be to use .NET's new XML API (namely LINQ to XML).
Here is an example:
using System;
using System.Linq;
using System.Xml.Linq;
class Program
{
static void Main()
{
String xml = #"<Root><Value></Value></Root>";
var elements = XDocument.Parse(xml)
.Descendants("Value")
.Select(e => e.Value);
}
}
http://msdn.microsoft.com/en-us/library/system.xml.xmlnode.value(VS.71).aspx
Because the "value" returned depends on the NodeType, there is a chance that the node will be interpreted as a type that can return NULL.
You might be better off using:
XmlElement elem = ....
string s = elem.SelectSingleNode("somepath").InnerText;
as XMLNode.InnerText (or XmlNode.InnerXML) will return a string, including an empty string.
Maybe this will work for you:
string s = elem.SelectSingleNode("somepath") != null ? elem.SelectSingleNode("somepath").value : ""
When I'm actually bothering with XML DOM, you could write a helper method along the lines of:
static string NodeValue(XmlNode node, string defaultValue)
{
if (node != null)
return node.Value ?? defaultValue;
return defaultValue;
}
Then you can do the following if you're not sure your node will exist:
string s = NodeValue(elem.SelectSingleNode("Type"), String.Empty);
If keeps your code readable, especially if you're doing this for multiple elements.
All that being said, SelectSingleNode(..) does not return a null value if the tag is empty. The Value attribute will be null however. If you're just trying to work around that, this should do:
string s = elem.SelectSingleNode("Type").Value ?? String.Empty;
Edit: ah, you're using /text() to select the actual text node. You could just get rid of that part of the XPath, but the NodeValue method I supplied should still work (the "?? defaultValue" part is not needed in that case though).