I would like to XML serialize an object that has (among other) a property of type IModelObject (which is an interface).
public class Example
{
public IModelObject Model { get; set; }
}
When I try to serialize an object of this class, I receive the following error:
"Cannot serialize member Example.Model of type Example because it is an interface."
I understand that the problem is that an interface cannot be serialized. However, the concrete Model object type is unknown until runtime.
Replacing the IModelObject interface with an abstract or concrete type and use inheritance with XMLInclude is possible, but seems like an ugly workaround.
Any suggestions?
This is simply an inherent limitation of declarative serialization where type information is not embedded within the output.
On trying to convert <Flibble Foo="10" /> back into
public class Flibble { public object Foo { get; set; } }
How does the serializer know whether it should be an int, a string, a double (or something else)...
To make this work you have several options but if you truly don't know till runtime the easiest way to do this is likely to be using the XmlAttributeOverrides.
Sadly this will only work with base classes, not interfaces. The best you can do there is to ignore the property which isn't sufficient for your needs.
If you really must stay with interfaces you have three real options:
Hide it and deal with it in another property
Ugly, unpleasant boiler plate and much repetition but most consumers of the class will not have to deal with the problem:
[XmlIgnore()]
public object Foo { get; set; }
[XmlElement("Foo")]
[EditorVisibile(EditorVisibility.Advanced)]
public string FooSerialized
{
get { /* code here to convert any type in Foo to string */ }
set { /* code to parse out serialized value and make Foo an instance of the proper type*/ }
}
This is likely to become a maintenance nightmare...
Implement IXmlSerializable
Similar to the first option in that you take full control of things but
Pros
You don't have nasty 'fake' properties hanging around.
you can interact directly with the xml structure adding flexibility/versioning
Cons
you may end up having to re-implement the wheel for all the other properties on the class
Issues of duplication of effort are similar to the first.
Modify your property to use a wrapping type
public sealed class XmlAnything<T> : IXmlSerializable
{
public XmlAnything() {}
public XmlAnything(T t) { this.Value = t;}
public T Value {get; set;}
public void WriteXml (XmlWriter writer)
{
if (Value == null)
{
writer.WriteAttributeString("type", "null");
return;
}
Type type = this.Value.GetType();
XmlSerializer serializer = new XmlSerializer(type);
writer.WriteAttributeString("type", type.AssemblyQualifiedName);
serializer.Serialize(writer, this.Value);
}
public void ReadXml(XmlReader reader)
{
if(!reader.HasAttributes)
throw new FormatException("expected a type attribute!");
string type = reader.GetAttribute("type");
reader.Read(); // consume the value
if (type == "null")
return;// leave T at default value
XmlSerializer serializer = new XmlSerializer(Type.GetType(type));
this.Value = (T)serializer.Deserialize(reader);
reader.ReadEndElement();
}
public XmlSchema GetSchema() { return(null); }
}
Using this would involve something like (in project P):
public namespace P
{
public interface IFoo {}
public class RealFoo : IFoo { public int X; }
public class OtherFoo : IFoo { public double X; }
public class Flibble
{
public XmlAnything<IFoo> Foo;
}
public static void Main(string[] args)
{
var x = new Flibble();
x.Foo = new XmlAnything<IFoo>(new RealFoo());
var s = new XmlSerializer(typeof(Flibble));
var sw = new StringWriter();
s.Serialize(sw, x);
Console.WriteLine(sw);
}
}
which gives you:
<?xml version="1.0" encoding="utf-16"?>
<MainClass
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<Foo type="P.RealFoo, P, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null">
<RealFoo>
<X>0</X>
</RealFoo>
</Foo>
</MainClass>
This is obviously more cumbersome for users of the class though avoids much boiler plate.
A happy medium may be merging the XmlAnything idea into the 'backing' property of the first technique. In this way most of the grunt work is done for you but consumers of the class suffer no impact beyond confusion with introspection.
The solution to this is using reflection with the DataContractSerializer. You don't even have to mark your class with [DataContract] or [DataMember]. It will serialize any object, regardless of whether it has interface type properties (including dictionaries) into xml. Here is a simple extension method that will serialize any object into XML even if it has interfaces (note you could tweak this to run recursively as well).
public static XElement ToXML(this object o)
{
Type t = o.GetType();
Type[] extraTypes = t.GetProperties()
.Where(p => p.PropertyType.IsInterface)
.Select(p => p.GetValue(o, null).GetType())
.ToArray();
DataContractSerializer serializer = new DataContractSerializer(t, extraTypes);
StringWriter sw = new StringWriter();
XmlTextWriter xw = new XmlTextWriter(sw);
serializer.WriteObject(xw, o);
return XElement.Parse(sw.ToString());
}
what the LINQ expression does is it enumerates each property,
returns each property that is an interface,
gets the value of that property (the underlying object),
gets the type of that concrete object
puts it into an array, and adds that to the serializer's list of known types.
Now the serializer knows how about the types it is serializing so it can do its job.
If you know your interface implementors up-front there's a fairly simple hack you can use to get your interface type to serialize without writing any parsing code:
public interface IInterface {}
public class KnownImplementor01 : IInterface {}
public class KnownImplementor02 : IInterface {}
public class KnownImplementor03 : IInterface {}
public class ToSerialize {
[XmlIgnore]
public IInterface InterfaceProperty { get; set; }
[XmlArray("interface")]
[XmlArrayItem("ofTypeKnownImplementor01", typeof(KnownImplementor01))]
[XmlArrayItem("ofTypeKnownImplementor02", typeof(KnownImplementor02))]
[XmlArrayItem("ofTypeKnownImplementor03", typeof(KnownImplementor03))]
public object[] InterfacePropertySerialization {
get { return new[] { InterfaceProperty }; ; }
set { InterfaceProperty = (IInterface)value.Single(); }
}
}
The resulting xml should look something along the lines of
<interface><ofTypeKnownImplementor01><!-- etc... -->
You can use ExtendedXmlSerializer. This serializer support serialization of interface property without any tricks.
var serializer = new ConfigurationContainer().UseOptimizedNamespaces().Create();
var obj = new Example
{
Model = new Model { Name = "name" }
};
var xml = serializer.Serialize(obj);
Your xml will look like:
<?xml version="1.0" encoding="utf-8"?>
<Example xmlns:exs="https://extendedxmlserializer.github.io/v2" xmlns="clr-namespace:ExtendedXmlSerializer.Samples.Simple;assembly=ExtendedXmlSerializer.Samples">
<Model exs:type="Model">
<Name>name</Name>
</Model>
</Example>
ExtendedXmlSerializer support .net 4.5 and .net Core.
Replacing the IModelObject interface with an abstract or concrete type and use inheritance with XMLInclude is possible, but seems like an ugly workaround.
If it is possible to use an abstract base I would recommend that route. It will still be cleaner than using hand-rolled serialization. The only trouble I see with the abstract base is that your still going to need the concrete type? At least that is how I've used it in the past, something like:
public abstract class IHaveSomething
{
public abstract string Something { get; set; }
}
public class MySomething : IHaveSomething
{
string _sometext;
public override string Something
{ get { return _sometext; } set { _sometext = value; } }
}
[XmlRoot("abc")]
public class seriaized
{
[XmlElement("item", typeof(MySomething))]
public IHaveSomething data;
}
Unfortunately there's no simple answer, as the serializer doesn't know what to serialize for an interface. I found a more complete explaination on how to workaround this on MSDN
Unfortuantely for me, I had a case where the class to be serialized had properties that had interfaces as properties as well, so I needed to recursively process each property. Also, some of the interface properties were marked as [XmlIgnore], so I wanted to skip over those. I took ideas that I found on this thread and added some things to it to make it recursive. Only the deserialization code is shown here:
void main()
{
var serializer = GetDataContractSerializer<MyObjectWithCascadingInterfaces>();
using (FileStream stream = new FileStream(xmlPath, FileMode.Open))
{
XmlDictionaryReader reader = XmlDictionaryReader.CreateTextReader(stream, new XmlDictionaryReaderQuotas());
var obj = (MyObjectWithCascadingInterfaces)serializer.ReadObject(reader);
// your code here
}
}
DataContractSerializer GetDataContractSerializer<T>() where T : new()
{
Type[] types = GetTypesForInterfaces<T>();
// Filter out duplicates
Type[] result = types.ToList().Distinct().ToList().ToArray();
var obj = new T();
return new DataContractSerializer(obj.GetType(), types);
}
Type[] GetTypesForInterfaces<T>() where T : new()
{
return GetTypesForInterfaces(typeof(T));
}
Type[] GetTypesForInterfaces(Type T)
{
Type[] result = new Type[0];
var obj = Activator.CreateInstance(T);
// get the type for all interface properties that are not marked as "XmlIgnore"
Type[] types = T.GetProperties()
.Where(p => p.PropertyType.IsInterface &&
!p.GetCustomAttributes(typeof(System.Xml.Serialization.XmlIgnoreAttribute), false).Any())
.Select(p => p.GetValue(obj, null).GetType())
.ToArray();
result = result.ToList().Concat(types.ToList()).ToArray();
// do the same for each of the types identified
foreach (Type t in types)
{
Type[] embeddedTypes = GetTypesForInterfaces(t);
result = result.ToList().Concat(embeddedTypes.ToList()).ToArray();
}
return result;
}
I have found a simpler solution (you don't need the DataContractSerializer), thanks to this blog here:
XML serializing derived types when base type is in another namespace or DLL
But 2 problems can rise in this implementation:
(1) What if DerivedBase is not in the namespace of class Base, or even worse in a project that depends on Base namespace, so Base cannot XMLInclude DerivedBase
(2) What if we only have class Base as a dll ,so again Base cannot XMLInclude DerivedBase
Till now, ...
So the solution to the 2 problems is by using XmlSerializer Constructor (Type, array[]) :
XmlSerializer ser = new XmlSerializer(typeof(A), new Type[]{ typeof(DerivedBase)});
A detailed example is provided here on MSDN:
XmlSerializer Constructor (Type, extraTypesArray[])
It seems to me that for DataContracts or Soap XMLs, you need to check the XmlRoot as mentioned here in this SO question.
A similar answer is here on SO but it isn't marked as one, as it not the OP seems to have considered it already.
in my project, I have a
List<IFormatStyle> FormatStyleTemplates;
containing different Types.
I then use the solution 'XmlAnything' from above, to serialize this list of different types.
The generated xml is beautiful.
[Browsable(false)]
[EditorBrowsable(EditorBrowsableState.Never)]
[XmlArray("FormatStyleTemplates")]
[XmlArrayItem("FormatStyle")]
public XmlAnything<IFormatStyle>[] FormatStyleTemplatesXML
{
get
{
return FormatStyleTemplates.Select(t => new XmlAnything<IFormatStyle>(t)).ToArray();
}
set
{
// read the values back into some new object or whatever
m_FormatStyleTemplates = new FormatStyleProvider(null, true);
value.ForEach(t => m_FormatStyleTemplates.Add(t.Value));
}
}
Using JSON.net, I want to deserialize a list of types that inherit from an abstract class. I have used KnownTypesBinder (source) like
var jsonSettings = GlobalConfiguration.Configuration.Formatters.JsonFormatter.SerializerSettings;
jsonSettings.TypeNameHandling = TypeNameHandling.Auto;
jsonSettings.Binder = new KnownTypesBinder { KnownTypes = new List<Type> { ... } };
Now this works perfectly fine in the WEB API modelbinder; KnownTypesBinder.BindToType is being called an the object can be deserialized. In a different part of the web application I have to deserialize a JSON string, so I would like to re-use the same JsonFormatter. According to the docs, the following should work;
JsonConvert.DeserializeObject<T>(String, JsonSerializerSettings);
However when I do just that:
JsonConvert.DeserializeObject<A>(jsonString, GlobalConfiguration.Configuration.Formatters.JsonFormatter.SerializerSettings);
The following error is thrown:
JsonSerializationException. Could not create an instance of type C. Type is an interface or abstract class and cannot be instantiated.
My types look something like this;
class A {
public B B { get; set; }
}
class B {
public List<C> C { get; set; }
}
abstract class C { }
class C1: C { }
class C2: C { }
Also creating a new JsonSerializerSettings and setting Binder and TypeNameHandling makes no difference. I found that KnownTypesBinder.BindToType is not being called at all. Is there something in JSON.net that I'm missing?
Feeling stupid here. The discriminator used by JSON.net is called "$type". As I was using curl to send the POST payload, bash tried to resolve $type to an environment variable. As there was no such variable, the final JSON was simply {"": "C"} instead of {"$type": "C"}.
So I have an Object called FormType.
It contains some strings, booleans etc.
But FormType also contains this:
private IList<FormTypeVersion> _versions = new List<FormTypeVersion>();
public virtual IList<FormTypeVersion> Versions
{
get { return _versions; }
set { _versions = value; }
}
Is this why I am getting this error:
{"Cannot serialize member 'Domain.FormType.Versions' of type 'System.Collections.Generic.IList`1
Also - FormTypeVersion also contains some ILists.
How can I get round this error, it happens at this line:
var xm = new XmlSerializer(typeof(T));
The XmlSerializer cannot deserialize interfaces (unless you want to implement IXmlSerializable yourself on the FormType object). That is why you are seeing that exception.
If you change your IList to List it should work like in the following example:
[Serializable]
public class FormType
{
private List<FormTypeVersion> _versions = new List<FormTypeVersion>();
public virtual List<FormTypeVersion> Versions
{
get { return _versions; }
set { _versions = value; }
}
}
If you don't have the luxury to change your type from IList to List, then the cleanest approach is to implement IXmlSerializable. There are other solutions using abstract types, reflection and similar, but i wouldn't call that clean.
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Dynamically implementing an interface in .NET 4.0 (C#)
cast anonymous type to an interface?
Is there a way to "cast" an anonymous type to a specific interface ? I know I can create a class who implement this interface but I don't need this class, I have to return an interface.
I need a solution without third party library
Thanks,
var result =
(from a in context.TABLE1
join b in context.TABLE2 on a.Table2Id equals b.Id
select new
{
Table1Field1 = a.Field1,
Table2Field1 = b.Field1,
....
}).ToList<IMyClass>();
public interface IMyClass
{
string Table1Field1 { get; set; }
string Table1Field2 { get; set; }
string Table2Field1 { get; set; }
}
This is impossible. Why? Because an anonymous type is a syntactic sugar. Anonymous types are a design-time feature meaning that compiler will generate an actual type with a very strange name, but it's like any other type after all.
Sadly, C# doesn't have interface auto-implementation. That is, you need to implement an interface in a named type.
UPDATE
Want to workaround this limitation?
You can use inversion of control (either using an API like Castle Windsor or just by hand).
Check this sample code I made just now:
public static class AnonymousExtensions
{
public static T To<T>(this object anon)
{
// #1 Obtain the type implementing the whole interface
Type implementation = Assembly.GetExecutingAssembly()
.GetTypes()
.SingleOrDefault(t => t.GetInterfaces().Contains(typeof(T)));
// #2 Once you've the implementation type, you create an instance of it
object implementationInstance = Activator.CreateInstance(implementation, false);
// #3 Now's time to set the implementation properties based on
// the anonyous type instance property values!
foreach(PropertyInfo property in anon.GetType().GetProperties(BindingFlags.Instance | BindingFlags.Public))
{
// Has the implementation this anonymous type property?
if(implementation.GetProperty(property.Name) != null)
{
// Setting the implementation instance property with the anonymous
// type instance property's value!
implementation.GetProperty(property.Name).SetValue(implementationInstance, property.GetValue(anon, null));
}
}
return (T)implementationInstance;
}
}
Design and implement some interface...
// Some interface
public interface IHasText
{
string Text { get; set; }
}
// An implementation for the interface
public class HasText : IHasText
{
public string Text
{
get;
set;
}
}
Now use the whole extension method somewhere!
var anonymous = new { Text = "Hello world!" };
IHasText hasTextImplementation = anonymous.To<IHasText>();
hasTextImplementation will have a HasText implementation instance! Or in other words: Text property will contain Hello world!.
Note that this code can be tweaked in order to support base and abstract classes, but I believe that this is enough to get the basic information to improve it as you want and for your needs.
I have a list of objects that implement a common interface. If I try to simply serialize it I get a nice exception that tells me that the serializer cannot serialize interfaces:
private readonly ObservableCollection<ICanHasInterface> children = new ObservableCollection<ICanHasInterface>();
public ObservableCollection<ICanHasInterface> Children
{
get { return children; }
}
=> "Cannot serialize member ... of type ... because it is an interface"
Apparently asking the serializer to get the type of the objects and mark the XmlElement with the attribute xsi:type (which is done if an object inherits from another class) is too much.
So because I do not want to implement IXmlSerializable, I thought up a workaround which looked promising initially:
private readonly ObservableCollection<ICanHasInterface> children = new ObservableCollection<ICanHasInterface>();
[XmlIgnore()]
public ObservableCollection<ICanHasInterface> Children
{
get { return children; }
}
[XmlElement("Child")]
public List<object> ChildrenSerialized
{
get
{
return new List<object>(Children);
}
set
{
Children.Clear();
foreach (var child in value)
{
if (child is ICanHasInterface) AddChild(child as ICanHasInterface);
}
}
}
With this at least the serialisation works just fine (Note: Either specify XmlInclude attributes for the types that can be in the original list or hand over an array of types in the constructor of the serializer), however if the object is deserialized the Children collection ends up empty because the set block is never reached during deserialization, I am quite clueless as to why this is; any ideas?
On deserialization the serializer uses your property getter to get the collection instance and then calls Add() on it for each item. It does not call your property setter. Something like this:
YourClass c = new YourClass();
c.ChildrenSerialized.Add(ReadValue());
...
In order to keep the collections synchronized you'd need to customize the Add() behavior of the collection you return from the property getter.
A better option is to change the ChildrenSerialized property to use an object[]. For arrays, the serializer reads the value into an array and then calls your property setter with the value.