I have a class that I want to serialise to XML. The name of outer element of the class when serialised needs to be controlled by the application.
At design time I know the element name can be controlled by the use an XmlTypeAttribute
[XmlElement(Name="MyName")]
I need to control this at run time so this will not work for me.
I also looked at IXmlSerializable to create my own serialisation code, but again this will not work as this only allows control of the 'internals' of the class and not the external wrapper.
Are there any other options available?
Yes, as Cheeso pointed out in the comments you can do this using XmlAttributeOverrides
XmlAttributes overrideAttributes = new XmlAttributes();
overrideAttributes.XmlRoot = new XmlRootAttribute("Testing");
XmlAttributeOverrides overrides = new XmlAttributeOverrides();
overrides.Add(typeof(string[]), overrideAttributes);
XmlSerializer serialise = new XmlSerializer(typeof(string[]), overrides);
using (MemoryStream stream = new MemoryStream())
{
serialise.Serialize(stream, new string[] { Guid.NewGuid().ToString(), Guid.NewGuid().ToString() });
}
Output:
<?xml version="1.0"?>
<Testing xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<string>37d47837-62d0-46dc-9747-709b91bdac6e</string>
<string>9cd904a9-f86f-46c1-a2aa-49c44bc3c654</string>
</Testing>
Xml serialisation (roughly) works on the basis that:
The object being serialised decides how its contents are serialised (including attributes of the root element)
However the caller is responsible for creating the root element (and consuming it on deserialisation).
You can see this from the way that the IXmlSerializable interface works - The object being serialised can use the XmlRootAttribute attribute as a suggestion to the caller on what the root element should look like, however ultimately it is up to the caller to create the root element (normally hanled by the XmlSerializer class).
Related
Is there something I need to configure in the XmlReaderSettings to encourage .net (4.8, 6, 7) to handle some cXML without throwing the following exception:
Unhandled exception. System.Xml.Schema.XmlSchemaException: The parameter entity replacement text must nest properly within markup declarations.
Sample cXML input
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE cXML SYSTEM "http://xml.cxml.org/schemas/cXML/1.2.041/cXML.dtd">
<cXML payloadID="donkeys#example.com" timestamp="2023-02-13T01:01:01Z">
<Header>
</Header>
<Request deploymentMode="production">
</Request>
</cXML>
Sample Application
using System.Xml;
using System.Xml.Linq;
namespace Donkeys
{
internal class Program
{
static void Main()
{
XmlReaderSettings settings = new()
{
XmlResolver = new XmlUrlResolver(),
DtdProcessing = DtdProcessing.Parse,
ValidationType = ValidationType.DTD,
};
FileStream fs = File.OpenRead("test.xml"); // sample cXML from question
XmlReader reader = XmlReader.Create(fs, settings);
XDocument.Load(reader); // this blows up
}
}
}
I'm looking to use the XmlUrlResolver to cache the DTDs but without ignoring the validation I get the error above but i'm not really sure why?
So far I've tried different validation flags but they don't validate at all unless I use ValidationType.DTD which goes pop.
The actual resolver seems to work fine; if I subclass it, it is returning the DTD (as a MemoryStream) as expected.
I can add an event handler to ignore the issue but this feels lamer than I'd like.
using System.Xml;
using System.Xml.Linq;
namespace Donkeys
{
internal class Program
{
static void Main()
{
XmlReaderSettings settings = new()
{
XmlResolver = new XmlUrlResolver(),
DtdProcessing = DtdProcessing.Parse,
ValidationType = ValidationType.DTD,
IgnoreComments = true
};
settings.ValidationEventHandler += Settings_ValidationEventHandler;
FileStream fs = File.OpenRead("test.xml");
XmlReader reader = XmlReader.Create(fs, settings);
XDocument dogs = XDocument.Load(reader);
}
private static void Settings_ValidationEventHandler(object? sender, System.Xml.Schema.ValidationEventArgs e)
{
// this seems fragile
if (e.Message.ToLower() == "The parameter entity replacement text must nest properly within markup declarations.".ToLower()) // and this would be a const
return;
throw e.Exception;
}
}
}
I've spent some time over the last few days looking into this and trying to get my head around what's going on here.
As far as I can tell, the error The parameter entity replacement text must nest properly within markup declarations is being reported incorrectly. My understanding of the spec is that this message means that you have mismatched < and > elements in the replacement text of a parameter entity in a DTD.
The following example is taken from this O'Reilly book sample page and demonstrates something that genuinely should reproduce this error:
<!ENTITY % finish_it ">">
<!ENTITY % bad "won't work" %finish_it;
Indeed the .NET DTD parser reports the same error for these two lines of DTD.
This doesn't mean you can't have < and > characters in parameter entity replacement text at all: the following two lines will declare an empty element with name Z, albeit in a somewhat round-about way:
<!ENTITY % Nested "<!ELEMENT Z EMPTY>">
%Nested;
The .NET DTD parser parses this successfully.
However, the .NET DTD parser appears to be objecting to this line in the cXML DTD, which defines the Object.ANY parameter entity:
<!ENTITY % Object.ANY '|xades:QualifyingProperties|cXMLSignedInfo|Extrinsic'>
There are of course no < and > characters in the replacement text, so the error is baffling.
This is by no means a new problem. I found this unanswered Stack Overflow question which basically reports the same problem. Also, this MSDN Forum post basically has the same problem, and it was asked in 2007. So is this unclear but intentional behaviour, or a bug that has been in .NET for 15+ years? I don't know.
For those who do want to look into things further, the following is about the minimum necessary to reproduce the problem. The necessary C# code to read the XML file can be taken from the question and adapted, I don't see the need to repeat it here:
example.dtd:
<?xml version="1.0" encoding="UTF-8"?>
<!ELEMENT A EMPTY>
<!ENTITY % Rest '|A' >
<!ELEMENT example (#PCDATA %Rest;)*>
example.xml:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE example SYSTEM "example.dtd">
<example/>
There are various ways to tweak this to get rid of the error. One way is to move the | character from the parameter entity into the ELEMENT example declaration. Replacing #PCDATA with another element (which you would also have to define) is another way.
But enough of the theory behind the problem. How can you actually move forwards with this?
I would take a local copy of the cXML DTD and adjust it to work around this error. You can download the DTD from the URL in your sample cXML input. The %Object.ANY; parameter entity is only used once in the DTD: I would replace this one occurrence with the replacement text, |xades:QualifyingProperties|cXMLSignedInfo|Extrinsic.
You then need to adjust the .NET XML parser to use your modified copy of the cXML DTD instead of fetching the the one from the given URL. You create a custom URL resolver for this, for example:
using System.Xml;
namespace Donkeys
{
internal class CXmlUrlResolver : XmlResolver
{
private static readonly Uri CXml1_2_041 = new Uri("http://xml.cxml.org/schemas/cXML/1.2.041/cXML.dtd");
private readonly XmlResolver urlResolver;
public CXmlUrlResolver()
{
this.urlResolver = new XmlUrlResolver();
}
public override object GetEntity(Uri absoluteUri, string role, Type ofObjectToReturn)
{
if (absoluteUri == CXml1_2_041)
{
// Return a Stream that reads from your custom version of the DTD,
// for example:
return File.OpenRead(#"SomeFilePathHere\cXML-1.2.401.dtd");
}
return this.urlResolver.GetEntity(absoluteUri, role, ofObjectToReturn);
}
}
}
This checks to see what URI is being requested, and if it matches the cXML URI, returns a stream that reads from your customised copy of the DTD. If some other URI is given, it passes the request to the nested XMLResolver, which then deals with it. You will of course need to use an instance of CXmlUrlResolver instead of XmlUrlResolver() when creating your XmlReaderSettings.
I don't know how many versions of cXML you will have to deal with, but if you are dealing with multiple versions, you might have to create a custom copy of the DTD for each version, and have your resolver return the correct local copy for each different URI.
A similar approach is given at this MSDN Forums post from 2008, which also deals with difficulties parsing cXML with .NET. This features a custom URL resolver created by subclassing XmlUrlResolver. Those who prefer composition over inheritance may prefer my custom URL resolver instead.
I have the following xml:
XML
I have the following C# class
C# GlobalClass
I am trying to convert the xml content into C# custom object like that:
string xmlFilePath = Android.OS.Environment.ExternalStorageDirectory.ToString() + "/Settings4/settings.xml";
XmlSerializer deserializer = new XmlSerializer(typeof(GlobalClass));
TextReader textReader = new StreamReader(xmlFilePath);
GlobalClass globalVariables;
globalVariables = (GlobalClass)deserializer.Deserialize(textReader);
textReader.Close();
But I get
There is an error in XML document
on the line of code
globalVariables = (GlobalClass)deserializer.Deserialize(textReader);
I make GlobalClass inherit from Application because I want GlobalClass to be global that is to say I want to use its properties throughout all activities. What I'm doing wrong to recieve that error?
In your class put something like this [Serializable, XmlRoot("YourRoot")]
When you work with deserialization it might not found.
From MSDN
The name of the XML root element that is generated and recognized in
an XML-document instance. The default is the name of the serialized
class.
I usually search the web high and low for my answers but this time I am drawing a blank. I'm using VS2005 to write code to POST xml to an API. I have classes setup in C# that I serialize into an XML document. The classes are below:
[Serializable]
[XmlRoot(Namespace = "", IsNullable = false)]
public class Request
{
public RequestIdentify Identify;
public string Method;
public string Params;
}
[Serializable]
public class RequestIdentify
{
public string StoreId;
public string Password;
}
When I serialize this I get:
<?xml version="1.0" encoding="UTF-8"?>
<Request xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<Identify>
<StoreId>00</StoreId>
<Password>removed for security</Password>
</Identify>
<Method>ProductExport</Method>
<Params />
</Request>
But the API returns a "No XML sent" error.
If I send the xml directly in a string as:
string xml = #"<Request><Identify><StoreId>00</StoreId><Password>Removed for security</Password></Identify><Method>ProductExport</Method><Params /></Request>";
effectively sending this xml (without the schema info in the "Request" tag):
<Request>
<Identify>
<StoreId>00</StoreId>
<Password>Removed for security</Password>
</Identify>
<Method>ProductExport</Method>
<Params />
</Request>
It seems to recognise the XML no problem.
So my question I guess is how can I change my current classes to Serialize into XML and get the XML as in the second case? I assume I need another "parent" class to wrap around the existing ones and use InnerXml property on this "parent" or something similar but I don't know how to do this.
Apologies for the question, I've only been using C# for 3 months and I'm a trainee developer who is having to teach himself on the job!
Oh and PS I don't know why but VS2005 really does not want to let me set these classes up with private variables and then use getters and setters on public equivalents so I have them written how they are for now.
Thanks in advance :-)
UPDATE:
As with most things it's very hard to find answers if you're not sure what you need to ask or how to word it but:
Once I knew what to look for I found the answers I needed:
Removing the XML declaration:
XmlWriterSettings writerSettings = new XmlWriterSettings();
writerSettings.OmitXmlDeclaration = true;
StringWriter stringWriter = new StringWriter();
using (XmlWriter xmlWriter = XmlWriter.Create(stringWriter, writerSettings))
{
serializer.Serialize(xmlWriter, request);
}
string xmlText = stringWriter.ToString();
Removing/Setting the namespace (Thanks to above replies that helped find this one!):
XmlSerializerNamespaces ns = new XmlSerializerNamespaces();
ns.Add("", "");
Thanks for your help everyone who answered or pointed me in the right direction! And yes I did find articles to read once I knew what I was asking :-) It's the first time I have come unstuck in 3 months of teaching myself so I think I'm doing pretty well...
From Rydal's blog:
The XmlDocument object by default assigns a namespace to the XML string and also includes the declaration as the first line of the XML document. I definitely do not need or use those, therefore, I need to remove them. Here is how you go about doing just that.
Removing declaration and namespaces from XML serialization
I'm trying to read an event log saved as an XML file from .Net / C#, the event log xml format looks (approximately) like this:
<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<Events>
<Event xmlns='http://schemas.microsoft.com/win/2004/08/events/event'>...</Event>
<Event xmlns='http://schemas.microsoft.com/win/2004/08/events/event'>...</Event>
</Events>
Where the ... bit is a relatively complex series of types defined in a schema file event.xsd.
My plan was to use XSD.exe to generate a C# wrapper type for reading this event log XML from this schema file and then deserialise the XML using the XmlSerializer class, like so:
using (FileStream stream = File.OpenRead(filename))
{
XmlSerializer serialiser = new XmlSerializer(typeof(Events));
return (Events)serialiser.Deserialize(stream);
}
The trouble is that the schema file doesn't contain a definition for the Events element (because its not in the schema), and so the above doesn't compile as there is no Events type.
I've tried a couple of variations, including using the type EventType[] instead of Events (which resulted in the exception " was not expected."). I also attempting to craft my own C# container Events type:
public class Events
{
[XmlElement]
public EventType[] Items
{
get;
set;
}
}
However the above simply results in the Items array being null.
How can I read Events Logs saved to XML format from C#?
So I managed this by using the following class:
[Serializable]
[XmlType(AnonymousType = true)]
[XmlRoot(Namespace = "", IsNullable = false)]
public class Events
{
[XmlElement("Event", Namespace = "http://schemas.microsoft.com/win/2004/08/events/event")]
public EventType[] Items
{
get;
set;
}
}
I'm not entirely certain what it is that made this work where previously it failed (I suspect its the Namespace property), however I found this out by using xsd.exe to generate a schema from a saved event log file and and then again to generate C# classes from that file, like so:
xsd /c eventlog.xml
xsd /c eventlog.xsd eventlog_app1.xsd
(Because it writes two xsd files you need to name both of them on the command line). I then looked at the resulting C# and compared / experimented until it worked.
I'm trying to write an IXmlSerializable class that stays synced with an XML file. The XML file has the following format:
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<logging>
<logLevel>Error</logLevel>
</logging>
...potentially other sections...
</configuration>
I have a DllConfig class for the whole XML file and a LoggingSection class for representing <logging> and its contents, i.e., <logLevel>. DllConfig has this property:
[XmlElement(ElementName = LOGGING_TAG_NAME,
DataType = "LoggingSection")]
public LoggingSection Logging { get; protected set; }
What I want is for the backing XML file to be updated (i.e., rewritten) when a property is set. I already have DllConfig do this when Logging is set. However, how should I go about doing this when Logging.LogLevel is set? Here's an example of what I mean:
var config = new DllConfig("path_to_backing_file.xml");
config.Logging.LogLevel = LogLevel.Information; // not using Logging setter, but a
// setter on LoggingSection, so how
// does path_to_backing_file.xml
// have its contents updated?
My current solution is to have a SyncedLoggingSection class that inherits from LoggingSection and also takes a DllConfig instance in the constructor. It declares a new LogLevel that, when set, updates the LogLevel in the base class and also uses the given DllConfig to write the entire DllConfig out to the backing XML file. Is this a good technique?
I don't think I can just serialize SyncedLoggingSection by itself to the backing XML file, because not all of the contents will be written, just the <logging> node. Then I'd end up with an XML file containing only the <logging> section with its updated <logLevel>, instead of the entire config file with <logLevel> updated. Hence, I need to pass an instance of DllConfig to SyncedLoggingSection.
It seems almost like I want an event handler, one in DllConfig that would notice when particular properties (i.e., LogLevel) in its properties (i.e., Logging) were set. Is such a thing possible?
Since you are implementing IXmlSerializable yourself, you can make DllConfig.Logging private. Then add a public method on DllConfig to set LogLevel instead of setting Logging.LogLevel directly. That will be the only way you can change the LogLevel. In the implementation of that public method, you can serialize the whole DllConfig to overwrite the xml.