When serializing a class I get an error if the XmlIgnore attribute is commented. When I uncomment the XmlIgnore attribute it works fine. Can anyone tell me why a property can't be serializable?
Normally, it will tell you why very clearly in the exception - look in particular at the InnerException; however, to summarise:
For a custom type SomeType to be serializable via XmlSerializer (either as the root object or via a property, i.e. public SomeType MemberName {get;set;})
it must be public
it must have a public parameterless constructor
a few generic combinations may not be supported
it must be expected (exposing data as object is a no-go, for example; subtypes of SomeType must be advertised in advance, typically via [XmlInclude(...)])
it must be concrete (non-abstract), or have concrete implementations defined via [XmlInclude(...)]
Using [XmlIgnore] removes the type from consideration, so types that are not xml-friendly can be avoided. You can also try IXmlSerializable for those cases
Related
Every time I meet this attribute, I always see such usage:
[DataContract]
class DataTransferObject
{
[DataMember]
public int Value {get;set;}
}
And in this example all inherited members should apply DataMember attribute to every property or field, this can lead to VERY clumsy and poilerplate code. But, recently I found (maybe secret feature?) a very elegant way of using it:
[DataContract]
public abstract class DTOBase
{
}
public class MyDTO : DTOBase
{
public int Value {get;set;}
public MyDTO(){} //important part is here
}
Important part: You should always explicitly define parameterless constructor, otherwise it won't serialize properly.
And yeah. It will serialize all its public members, no matter how deep will be inheritance, without need to apply attributes to members or class definitions.
Is this somehow documented somewhere (I didn't found)? Because, I were very supprized how much of boilerplate can be avoided.
Actually, you don't need to use DataContract and DataMember attributes if you don't want to, however they give you flexibility in defining what needs to be serialized and how.
I suggest starting with article Serializable Types on MSDN, it has a lot of information how Data Contract serializer works. Here are first 2 paragraphs, proving that you don't need to use attributes:
By default, the DataContractSerializer serializes all publicly visible
types.
All public read/write properties and fields of the type are
serialized. You can change the default behavior by applying the
DataContractAttribute and DataMemberAttribute attributes to the types
and members This feature can be useful in situations in which you have
types that are not under your control and cannot be modified to add
attributes. The DataContractSerializer recognizes such "unmarked"
types.
The main rules that apply to your case are:
DataContract attribute is not inherited. You can either apply it or not on your base class DTOBase, it is ignored in child class MyDTO. You can remove DataContract attribute from DTOBase class and result will be the same.
If you use DataContract attribute on a class, then only members that have DataMember attribute will be serialized. This is what happened in class DataTransferObject in your first sample.
If you do not use DataContract attribute on a class, then all public members of a class are serialized. This is what happened with your class MyDTO.
I am writing a Generic class that attempts to serialize an object of Type T as XML. Unfortunately (as I'm sure you know) not all objects can successfully be serialized as XML hence I would like to be able to write a constraint that specifies T can only be a class that is XML Serializable. Is this at all possible?
Pretty sure the answer to this is "no" but figured I would ask anyway in case there's something I have missed.
The only constraints available are:
class / struct
new()
BaseType / Interface
Of these, the only 2 that are slightly interesting are :new() (since XmlSerializer demands a public parameterless constructor) and :Interface (since IXmlSerializable is one of the options); however:
IXmlSerializable is not required, so that doesn't apply
no constraint here forces the type to be a public type (and a public type of a public type, in the case of nested types)
it doesn't account for the generics limitations
so in short: no, this isn't something you can enforce via generic constraints
You're right, the answer is no, you cannot constrain generic types to be XML serializable.
The reason for this, is that the XML Serializer has some very specific rules about what it will serialize (most notable, it serializes public properties only, and only types that have a public parameterless constructor). The factors that make a class XML serializable cannot be expressed in terms of types, and therefore there is no way to make a generic constraint for it.
You can constrain to an interface, so perhaps a solution would be to use a marker interface on your types that are XML serializable. Then again, this doesn't work if you don't control the types you want to serialize.
how can i serialize this class?
public class MyClass {
IInterface MyProperty { get; set;}
}
You need to add a setter to MyProperty as Xml serialization rules mandate that serialization must be able to round-trip i.e. it must be able to get the property for serialization, then set the property for deserialization.
As chibacity said, you need to add a setter to the property. You also need to add the XmlInclude attribute to the property to specify the possible implementing types, otherwise the XmlSerializer won't know what type to instantiate when deserializing
The XmlSerializer cannot serialize interfaces.
If you know the concrete types you will be dealing with in advance then you can use the XmlInclude approach. If not then there have been a few discussions about how to handle this:
XML serialization of interface
property
XmlSerialization with Interfaces
Serializing without XmlInclude
Make the class that implements IInterface Serializable like you normally would and it will all work.
I'm trying to serialize a type using the DataContractSerializer and am getting the exception below. This isn't for an SOA service, but I would still like to use the DataContractSerializer if possible. I am using .Net 3.5 SP1.
Type
'System.DelegateSerializationHolder+DelegateEntry'
with data contract name
'DelegateSerializationHolder.DelegateEntry:http://schemas.datacontract.org/2004/07/System'
is not expected. Add any types not
known statically to the list of known
types - for example, by using the
KnownTypeAttribute attribute or by
adding them to the list of known types
passed to DataContractSerializer.
Can you post your class definition?
It seems like you are trying to serialize a class which has a field of type delegate, which I'm pretty sure will make the serializer choke on.
Did you decorate your class with the DataContract / DataMember attributes? In 3.5 SP1 there is a default behavior for the serializer that serializes everything public in a class by default if it is not marked with those attributes. Maybe you should explicitely mark each property that needs to be serialized with a DataMember attribute and leave out those that should not be.
Other than that, we would need to see your class definition for more help.
There are 3 possible approaches to avoid the error described in http://blogs.microsoft.co.il/blogs/oshvartz/archive/2009/10/10/passing-event-handlers-over-wcf.aspx
I've been reading a text about an extension to C# and at one point it says that "An attribute decoration X may only be applied to fields of type Y."
I haven't been able to find a definition for attribute decoration, and I'm not making much sense out of this by exchanging the two.
It's probably referring to the Attribute class. For example, you can mark a type as serializable via the SerializableAttribute. When you apply an attribute, you can leave off the "Attribute" suffix.
[Serializable]
public class SomeClass {
}
Attributes provide a means to add meta-data about the code.
Attributes are used to add metadata to .NET (C#) code in a structured manner. What a lot of people don't realise, though, is that there are actually two types of attribute.
The simplest is custom attributes, where you define an attribute that specific classes look for to alter the way they work. A common example is the System.Xml.Serialization attributes which are read by the XmlSerializer to alter its output, e.g. a class could be marked up something like the following to specify its namespace and that the field should be an attribute:
[XmlType(Namespace = "http://mycompany.com/")]
public class MyClass
{
[XmlAttribute]
public string MyField;
}
Custom attributes like this have no meaning to the compiler or the runtime, they are just added to the class as part of its metadata, and can be retrieved by a call to Type.GetCustomAttributes.
The other main group of attributes is pseudo-custom attributes, which actually have meaning to either the compiler or the runtime. The example in the post by Haacked with SerializableAttribute is actually an example of a pseudo-custom attribute. It is actually stored as part of the type definition and cannot be retrieved using Type.GetCustomAttributes. You cannot create your own pseudo-custom attributes.
So it's likely what you're dealing with here is a custom attribute which is being looked for by a specific tool.