I have a class like this:
public class Data
{
public string Name { get; set; }
public int Size { get; set; }
public string Value { get; set; }
[NonSerialized] public byte[] Bytes;
}
When a List<Data> hits the serialization method below, it occasionally dies with
InvalidOperationException "This
XmlWriter does not support base64
encoded data."
As you can see, I am not directly encoding anything, just using the default serialization mechanism.
private static XDocument Serialize<T>( T source )
{
var target = new XDocument( );
var s = new XmlSerializer( typeof( T ) );
using( XmlWriter writer = target.CreateWriter( ) )
{
s.Serialize( writer, source );
}
return target;
}
The data will have Name properties that are English words separated by underscores. The Value property will by similar except with added math operators or numbers (they are mathematical expressions).
Does anyone know what is causing it and how I can correct it?
Use [XmlIgnore] instead of [NonSerialized]. The latter is for the SOAP and binary formatters, according to MSDN:
When using the BinaryFormatter or
SoapFormatter classes to serialize an
object, use the NonSerializedAttribute
attribute to prevent a field from
being serialized. For example, you can
use this attribute to prevent the
serialization of sensitive data.
The target objects for the
NonSerializedAttribute attribute are
public and private fields of a
serializable class. By default,
classes are not serializable unless
they are marked with
SerializableAttribute. During the
serialization process all the public
and private fields of a class are
serialized by default. Fields marked
with NonSerializedAttribute are
excluded during serialization. If you
are using the XmlSerializer class to
serialize an object, use the
XmlIgnoreAttribute class to get the
same functionality.
Mind you, I'm surprised your original code even compiles - when I try it, it says that [NonSerialized] can only be applied to fields...
Related
I am attempting to save/load a class to an xml file that contains generic types using a DataContractSerializer. I have the save working, but have realized I can't load it because I don't have the list of knownTypes for the deserializer.
Is there a way of serializing/deserializing this class that would allow me to deserialize it without referencing any of the stored types directly?
Here is my SessionVariables class that I am trying to save/load:
[DataContract]
public class SessionVariables
{
[DataMember]
private Dictionary<Type, ISessionVariables> _sessionVariables = new Dictionary<Type, ISessionVariables>();
private object _syncLock = new object();
public T Get<T>()
where T : ISessionVariables, new()
{
lock (_syncLock)
{
ISessionVariables vars = null;
if (_sessionVariables.TryGetValue(typeof(T), out vars))
return (T)vars;
vars = new T();
_sessionVariables.Add(typeof(T), vars);
return (T)vars;
}
}
public IList<Type> GetKnownTypes()
{
IList<Type> knownTypes = new List<Type>();
knownTypes.Add(this.GetType().GetType()); // adds System.RuntimeType
foreach (Type t in _sessionVariables.Keys)
{
if (!knownTypes.Contains(t))
knownTypes.Add(t);
}
return knownTypes;
}
}
The different modules of the application extend the ISessionVariables interface to create their own set of session variables, like this:
[DataContract]
public class ModuleASessionVariables : ISessionVariables
{
[DataMember]
public string ModuleA_Property1{ get; set; }
[DataMember]
public string ModuleA_Property2 { get; set; }
}
[DataContract]
public class ModuleBSessionVariables : ISessionVariables
{
[DataMember]
public string ModuleB_Property1{ get; set; }
[DataMember]
public string ModuleB_Property2 { get; set; }
}
And a singleton instance of the SessionVariables class is used to access session variables, like this:
singletonSessionVariables.Get<ModuleASessionVariables>().ModuleA_Property1
singletonSessionVariables.Get<ModuleBSessionVariables>().ModuleB_Property2
I got the save working like this:
using (FileStream writer = new FileStream(#"C:\test.txt", FileMode.Create))
{
DataContractSerializer dcs = new DataContractSerializer(typeof(SessionVariables), singletonSessionVariables.GetKnownTypes());
dcs.WriteObject(writer, singletonSessionVariables);
writer.Close();
}
However this method does not work to deserialize the class because I don't know it's known types.
Can I serialize and deserialize generic types when I don't have direct library references to any of the types used? And if so, how?
The problem here is that you aren't just wanting to serialize data, but you also want to serialize data about your data, i.e., (cue the dramatic chipmunk) metadata.
That metadata, in this case, are the types of the models that held the data originally. Normally, this isn't an issue, but as you've discovered if you're taking advantage of polymorphism in your design, your single collection may contain two or more different types, each of which needs to be deserialized to their original type.
This is usually accomplished by saving this Type metadata to the serialized result. Different serialization methods does this in different ways. Xaml serialization uses xml namespaces associated with .net namespaces, then names the elements after the original type name. Json.net accomplishes this via a specific named value saved to the json object.
The default DataContractSerializer is not Type aware. Therefore you need to replace it with a version that understands the .NET Type system and can serialize/deserialize Type metadata to the resulting xml. Luckily, one already exists in the framework, the NetDataContractSerializer.
And that's how you pad a link-only answer. The Aristocrats.
You could accomplish this using a custom DataContractResolver. This allows you to plug into the deserialization pipeline and provide a type to deserialize into based upon the type/namespace that is found in the serialized graph.
Here's a good article on it:
http://blogs.msdn.com/b/carlosfigueira/archive/2011/09/21/wcf-extensibility-data-contract-resolver.aspx
IDesign has an implementation of a resolver that can be used for dynamic discovery of types on their site: http://idesign.net/Downloads/GetDownload/1848 (you will probably have to make some modifications to handle generics)
I am having some trouble deserializing an object to XML. I am trying to deserialize something which doesn't have an empty constructor thus I need to use the BinaryFormatter? I have:
A DLL which consists of a class I want to deserialize into XML.
From reflecting the type I can see that it has no parameterless constructor.
This class contains properties of which some do not have empty constructors either.
My question is, is it possible to deserialize this class into XML? I did find a way whereby I used:
BinaryFormatter
Loaded the contents into a stream
Used a FileStream to write its contents but ended up with rubbish
Thanks in advance. I found something called FormatterServices... but don't know whether you could use this in conjunction with the XmlSerializer?
Deserialize the binary data back into an object.
Copy your object into a surrogate object.
Xml serialize your surrogate object.
Assume the type of your original non-xml serializable object is "Foo"
[XmlRoot]
public class FooSurrogate {
public FooSurrogate() { }; // note the empty constructor for xml deserialization
public FooSurrogate(Foo foo) { // this constructor is used in step 2
// in here you copy foo's state into this object's state
this.Prop1 = foo.Prop1; // this prop can be copied directly
this.Bar = new BarSurrogate(foo.Bar); // this prop needs a surrogate as well
}
[XmlAttribute] // note your surrogate can be used to xml-format too!
public string Prop1 { get; set; }
[XmlElement]
public BarSurrogate Bar { get; set; }
}
public class BarSurrogate {
...
}
Am I correct in thinking that, in order to get C# to serialize an object, I MUST have a public property for every field that needs its state stored?
If so, is that not very very sucky, as it weakens (if not breaks entirely) any encapsulation my class has?
In Java, XStream can iterate over every non-transient field and archive it. In C# this can't happen, and just to make things worse, things like Dictionaries don't serialize AT ALL. It's all a bit of a mess, no?
I've seen the DLL for a "port" of XStream to .net, but there are no docs and I'm suspicious.
You should use DataContractSerializer, and mark every property/field you want to serialize with [DataMember]. It doesn't care if your fields are private or public. By the way you can serialize Dictionaries with it...
[DataContract]
public class MyClass
{
[DataMember]
private string _privateField;
[DataMember]
public int PublicProperty { get; set;}
}
Serialization :
private static string SerializeXml<T>(T item)
{
DataContractSerializer ser = new DataContractSerializer(item.GetType());
StringBuilder sb = new StringBuilder();
XmlWriterSettings settings = new XmlWriterSettings { OmitXmlDeclaration = true, ConformanceLevel = ConformanceLevel.Fragment };
using (XmlWriter writer = new XmlWriter(sb, settings))
{
ser.WriteObject(writer, item);
}
return sb.ToString();
}
Look here for differences between XmlSerializer and DataContractSerializer : http://www.danrigsby.com/blog/index.php/2008/03/07/xmlserializer-vs-datacontractserializer-serialization-in-wcf/
The binaryformatter serializes private and even readonly fields without the need for properties. The XmlSerializer can only serialize with a public no-arg constructor and public properties. If you want to use XmlSerializer with encapsulation you can use IXmlSerializable, but that is rather painful.
If your object model is fairly simple or you can make it fairly simple by introducing special DTO:s for serialization (e.g. to avoid structs), then I recommend using a contract based serializer that can serialize private fields or properties. Have a look at protobuf-net.
Using C# .NET 2.0, I have a composite data class that does have the [Serializable] attribute on it. I am creating an XMLSerializer class and passing that into the constructor:
XmlSerializer serializer = new XmlSerializer(typeof(DataClass));
I am getting an exception saying:
There was an error reflecting type.
Inside the data class there is another composite object. Does this also need to have the [Serializable] attribute, or by having it on the top object, does it recursively apply it to all objects inside?
Look at the inner exception that you are getting. It will tell you which field/property it is having trouble serializing.
You can exclude fields/properties from xml serialization by decorating them with the [XmlIgnore] attribute.
XmlSerializer does not use the [Serializable] attribute, so I doubt that is the problem.
Remember that serialized classes must have default (i.e. parameterless) constructors. If you have no constructor at all, that's fine; but if you have a constructor with a parameter, you'll need to add the default one too.
I had a similar problem, and it turned out that the serializer could not distinguish between 2 classes I had with the same name (one was a subclass of the other). The inner exception looked like this:
'Types BaseNamespace.Class1' and 'BaseNamespace.SubNamespace.Class1' both use the XML type name, 'Class1', from namespace ''. Use XML attributes to specify a unique XML name and/or namespace for the type.
Where BaseNamespace.SubNamespace.Class1 is a subclass of BaseNamespace.Class1.
What I needed to do was add an attribute to one of the classes (I added to the base class):
[XmlType("BaseNamespace.Class1")]
Note: If you have more layers of classes you need to add an attribute to them as well.
Most common reasons by me:
- the object being serialized has no parameterless constructor
- the object contains Dictionary
- the object has some public Interface members
Also be aware that XmlSerializer cannot serialize abstract properties.. See my question here (which I have added the solution code to)..
XML Serialization and Inherited Types
All the objects in the serialization graph have to be serializable.
Since XMLSerializer is a blackbox, check these links if you want to debug further into the serialization process..
Changing where XmlSerializer Outputs Temporary Assemblies
HOW TO: Debug into a .NET XmlSerializer Generated Assembly
If you need to handle specific attributes (i.e. Dictionary, or any class), you can implement the IXmlSerialiable interface, which will allow you more freedom at the cost of more verbose coding.
public class NetService : IXmlSerializable
{
#region Data
public string Identifier = String.Empty;
public string Name = String.Empty;
public IPAddress Address = IPAddress.None;
public int Port = 7777;
#endregion
#region IXmlSerializable Implementation
public XmlSchema GetSchema() { return (null); }
public void ReadXml(XmlReader reader)
{
// Attributes
Identifier = reader[XML_IDENTIFIER];
if (Int32.TryParse(reader[XML_NETWORK_PORT], out Port) == false)
throw new XmlException("unable to parse the element " + typeof(NetService).Name + " (badly formatted parameter " + XML_NETWORK_PORT);
if (IPAddress.TryParse(reader[XML_NETWORK_ADDR], out Address) == false)
throw new XmlException("unable to parse the element " + typeof(NetService).Name + " (badly formatted parameter " + XML_NETWORK_ADDR);
}
public void WriteXml(XmlWriter writer)
{
// Attributes
writer.WriteAttributeString(XML_IDENTIFIER, Identifier);
writer.WriteAttributeString(XML_NETWORK_ADDR, Address.ToString());
writer.WriteAttributeString(XML_NETWORK_PORT, Port.ToString());
}
private const string XML_IDENTIFIER = "Id";
private const string XML_NETWORK_ADDR = "Address";
private const string XML_NETWORK_PORT = "Port";
#endregion
}
There is an interesting article, which show an elegant way to implements a sophisticated way to "extend" the XmlSerializer.
The article say:
IXmlSerializable is covered in the official documentation, but the documentation states it's not intended for public use and provides no information beyond that. This indicates that the development team wanted to reserve the right to modify, disable, or even completely remove this extensibility hook down the road. However, as long as you're willing to accept this uncertainty and deal with possible changes in the future, there's no reason whatsoever you can't take advantage of it.
Because this, I suggest to implement you're own IXmlSerializable classes, in order to avoid too much complicated implementations.
...it could be straightforward to implements our custom XmlSerializer class using reflection.
I just got the same error and discovered that a property of type IEnumerable<SomeClass> was the problem. It appears that IEnumerable cannot be serialized directly.
Instead, one could use List<SomeClass>.
I've discovered that the Dictionary class in .Net 2.0 is not serializable using XML, but serializes well when binary serialization is used.
I found a work around here.
I recently got this in a web reference partial class when adding a new property. The auto generated class was adding the following attributes.
[System.Xml.Serialization.XmlElementAttribute(Order = XX)]
I needed to add a similar attribute with an order one higher than the last in the auto generated sequence and this fixed it for me.
I too thought that the Serializable attribute had to be on the object but unless I'm being a complete noob (I am in the middle of a late night coding session) the following works from the SnippetCompiler:
using System;
using System.IO;
using System.Xml;
using System.Collections.Generic;
using System.Xml.Serialization;
public class Inner
{
private string _AnotherStringProperty;
public string AnotherStringProperty
{
get { return _AnotherStringProperty; }
set { _AnotherStringProperty = value; }
}
}
public class DataClass
{
private string _StringProperty;
public string StringProperty
{
get { return _StringProperty; }
set{ _StringProperty = value; }
}
private Inner _InnerObject;
public Inner InnerObject
{
get { return _InnerObject; }
set { _InnerObject = value; }
}
}
public class MyClass
{
public static void Main()
{
try
{
XmlSerializer serializer = new XmlSerializer(typeof(DataClass));
TextWriter writer = new StreamWriter(#"c:\tmp\dataClass.xml");
DataClass clazz = new DataClass();
Inner inner = new Inner();
inner.AnotherStringProperty = "Foo2";
clazz.InnerObject = inner;
clazz.StringProperty = "foo";
serializer.Serialize(writer, clazz);
}
finally
{
Console.Write("Press any key to continue...");
Console.ReadKey();
}
}
}
I would imagine that the XmlSerializer is using reflection over the public properties.
Sometime, this type of error is because you dont have constructur of class without argument
I had a situation where the Order was the same for two elements in a row
[System.Xml.Serialization.XmlElementAttribute(IsNullable = true, Order = 0, ElementName = "SeriousInjuryFlag")]
.... some code ...
[System.Xml.Serialization.XmlElementAttribute(IsNullable = true, Order = 0, ElementName = "AccidentFlag")]
When I changed the code to increment the order by one for each new Property in the class, the error went away.
I was getting the same error when I created a property having a datatype - Type. On this, I was getting an error - There was an error reflecting type. I kept checking the 'InnerException' of every exception from the debug dock and got the specific field name (which was Type) in my case. The solution is as follows:
[XmlIgnore]
public Type Type { get; set; }
Also note that you cannot serialize user interface controls and that any object you want to pass onto the clipboard must be serializable otherwise it cannot be passed across to other processes.
I have been using the NetDataSerialiser class to serialise
my domain classes. NetDataContractSerializer Class.
The domain classes are shared between client and server.
I had the same issue and in my case the object had a ReadOnlyCollection. A collection must implement Add method to be serializable.
I have a slightly different solution to all described here so far, so for any future civilisation here's mine!
I had declared a datatype of "time" as the original type was a TimeSpan and subsequently changed to a String:
[System.Xml.Serialization.XmlElementAttribute(DataType="time", Order=3)]
however the actual type was a string
public string TimeProperty {
get {
return this.timePropertyField;
}
set {
this.timePropertyField = value;
this.RaisePropertyChanged("TimeProperty");
}
}
by removing the DateType property the Xml can be serialized
[System.Xml.Serialization.XmlElementAttribute(Order=3)]
public string TimeProperty {
get {
return this.timePropertyField;
}
set {
this.timePropertyField = value;
this.RaisePropertyChanged("TimeProperty");
}
}
[System.Xml.Serialization.XmlElementAttribute("strFieldName", Form = System.Xml.Schema.XmlSchemaForm.Unqualified)]
Or
[XmlIgnore]
string [] strFielsName {get;set;}
Using C# .NET 2.0, I have a composite data class that does have the [Serializable] attribute on it. I am creating an XMLSerializer class and passing that into the constructor:
XmlSerializer serializer = new XmlSerializer(typeof(DataClass));
I am getting an exception saying:
There was an error reflecting type.
Inside the data class there is another composite object. Does this also need to have the [Serializable] attribute, or by having it on the top object, does it recursively apply it to all objects inside?
Look at the inner exception that you are getting. It will tell you which field/property it is having trouble serializing.
You can exclude fields/properties from xml serialization by decorating them with the [XmlIgnore] attribute.
XmlSerializer does not use the [Serializable] attribute, so I doubt that is the problem.
Remember that serialized classes must have default (i.e. parameterless) constructors. If you have no constructor at all, that's fine; but if you have a constructor with a parameter, you'll need to add the default one too.
I had a similar problem, and it turned out that the serializer could not distinguish between 2 classes I had with the same name (one was a subclass of the other). The inner exception looked like this:
'Types BaseNamespace.Class1' and 'BaseNamespace.SubNamespace.Class1' both use the XML type name, 'Class1', from namespace ''. Use XML attributes to specify a unique XML name and/or namespace for the type.
Where BaseNamespace.SubNamespace.Class1 is a subclass of BaseNamespace.Class1.
What I needed to do was add an attribute to one of the classes (I added to the base class):
[XmlType("BaseNamespace.Class1")]
Note: If you have more layers of classes you need to add an attribute to them as well.
Most common reasons by me:
- the object being serialized has no parameterless constructor
- the object contains Dictionary
- the object has some public Interface members
Also be aware that XmlSerializer cannot serialize abstract properties.. See my question here (which I have added the solution code to)..
XML Serialization and Inherited Types
All the objects in the serialization graph have to be serializable.
Since XMLSerializer is a blackbox, check these links if you want to debug further into the serialization process..
Changing where XmlSerializer Outputs Temporary Assemblies
HOW TO: Debug into a .NET XmlSerializer Generated Assembly
If you need to handle specific attributes (i.e. Dictionary, or any class), you can implement the IXmlSerialiable interface, which will allow you more freedom at the cost of more verbose coding.
public class NetService : IXmlSerializable
{
#region Data
public string Identifier = String.Empty;
public string Name = String.Empty;
public IPAddress Address = IPAddress.None;
public int Port = 7777;
#endregion
#region IXmlSerializable Implementation
public XmlSchema GetSchema() { return (null); }
public void ReadXml(XmlReader reader)
{
// Attributes
Identifier = reader[XML_IDENTIFIER];
if (Int32.TryParse(reader[XML_NETWORK_PORT], out Port) == false)
throw new XmlException("unable to parse the element " + typeof(NetService).Name + " (badly formatted parameter " + XML_NETWORK_PORT);
if (IPAddress.TryParse(reader[XML_NETWORK_ADDR], out Address) == false)
throw new XmlException("unable to parse the element " + typeof(NetService).Name + " (badly formatted parameter " + XML_NETWORK_ADDR);
}
public void WriteXml(XmlWriter writer)
{
// Attributes
writer.WriteAttributeString(XML_IDENTIFIER, Identifier);
writer.WriteAttributeString(XML_NETWORK_ADDR, Address.ToString());
writer.WriteAttributeString(XML_NETWORK_PORT, Port.ToString());
}
private const string XML_IDENTIFIER = "Id";
private const string XML_NETWORK_ADDR = "Address";
private const string XML_NETWORK_PORT = "Port";
#endregion
}
There is an interesting article, which show an elegant way to implements a sophisticated way to "extend" the XmlSerializer.
The article say:
IXmlSerializable is covered in the official documentation, but the documentation states it's not intended for public use and provides no information beyond that. This indicates that the development team wanted to reserve the right to modify, disable, or even completely remove this extensibility hook down the road. However, as long as you're willing to accept this uncertainty and deal with possible changes in the future, there's no reason whatsoever you can't take advantage of it.
Because this, I suggest to implement you're own IXmlSerializable classes, in order to avoid too much complicated implementations.
...it could be straightforward to implements our custom XmlSerializer class using reflection.
I just got the same error and discovered that a property of type IEnumerable<SomeClass> was the problem. It appears that IEnumerable cannot be serialized directly.
Instead, one could use List<SomeClass>.
I've discovered that the Dictionary class in .Net 2.0 is not serializable using XML, but serializes well when binary serialization is used.
I found a work around here.
I recently got this in a web reference partial class when adding a new property. The auto generated class was adding the following attributes.
[System.Xml.Serialization.XmlElementAttribute(Order = XX)]
I needed to add a similar attribute with an order one higher than the last in the auto generated sequence and this fixed it for me.
I too thought that the Serializable attribute had to be on the object but unless I'm being a complete noob (I am in the middle of a late night coding session) the following works from the SnippetCompiler:
using System;
using System.IO;
using System.Xml;
using System.Collections.Generic;
using System.Xml.Serialization;
public class Inner
{
private string _AnotherStringProperty;
public string AnotherStringProperty
{
get { return _AnotherStringProperty; }
set { _AnotherStringProperty = value; }
}
}
public class DataClass
{
private string _StringProperty;
public string StringProperty
{
get { return _StringProperty; }
set{ _StringProperty = value; }
}
private Inner _InnerObject;
public Inner InnerObject
{
get { return _InnerObject; }
set { _InnerObject = value; }
}
}
public class MyClass
{
public static void Main()
{
try
{
XmlSerializer serializer = new XmlSerializer(typeof(DataClass));
TextWriter writer = new StreamWriter(#"c:\tmp\dataClass.xml");
DataClass clazz = new DataClass();
Inner inner = new Inner();
inner.AnotherStringProperty = "Foo2";
clazz.InnerObject = inner;
clazz.StringProperty = "foo";
serializer.Serialize(writer, clazz);
}
finally
{
Console.Write("Press any key to continue...");
Console.ReadKey();
}
}
}
I would imagine that the XmlSerializer is using reflection over the public properties.
Sometime, this type of error is because you dont have constructur of class without argument
I had a situation where the Order was the same for two elements in a row
[System.Xml.Serialization.XmlElementAttribute(IsNullable = true, Order = 0, ElementName = "SeriousInjuryFlag")]
.... some code ...
[System.Xml.Serialization.XmlElementAttribute(IsNullable = true, Order = 0, ElementName = "AccidentFlag")]
When I changed the code to increment the order by one for each new Property in the class, the error went away.
I was getting the same error when I created a property having a datatype - Type. On this, I was getting an error - There was an error reflecting type. I kept checking the 'InnerException' of every exception from the debug dock and got the specific field name (which was Type) in my case. The solution is as follows:
[XmlIgnore]
public Type Type { get; set; }
Also note that you cannot serialize user interface controls and that any object you want to pass onto the clipboard must be serializable otherwise it cannot be passed across to other processes.
I have been using the NetDataSerialiser class to serialise
my domain classes. NetDataContractSerializer Class.
The domain classes are shared between client and server.
I had the same issue and in my case the object had a ReadOnlyCollection. A collection must implement Add method to be serializable.
I have a slightly different solution to all described here so far, so for any future civilisation here's mine!
I had declared a datatype of "time" as the original type was a TimeSpan and subsequently changed to a String:
[System.Xml.Serialization.XmlElementAttribute(DataType="time", Order=3)]
however the actual type was a string
public string TimeProperty {
get {
return this.timePropertyField;
}
set {
this.timePropertyField = value;
this.RaisePropertyChanged("TimeProperty");
}
}
by removing the DateType property the Xml can be serialized
[System.Xml.Serialization.XmlElementAttribute(Order=3)]
public string TimeProperty {
get {
return this.timePropertyField;
}
set {
this.timePropertyField = value;
this.RaisePropertyChanged("TimeProperty");
}
}
[System.Xml.Serialization.XmlElementAttribute("strFieldName", Form = System.Xml.Schema.XmlSchemaForm.Unqualified)]
Or
[XmlIgnore]
string [] strFielsName {get;set;}