CODEWITHSUNDEEP
c#.netxmlserializationserializable
Jon Mitchell
Jon Mitchell

Reputation: 3429

Serializing private member data

I'm trying to serialize an object to XML that has a number of properties, some of which are readonly.

public Guid Id { get; private set; }

I have marked the class [Serializable] and I have implemented the ISerializable interface.

Below is the code I'm using to serialize my object.

public void SaveMyObject(MyObject obj)
{
    XmlSerializer serializer = new XmlSerializer(typeof(MyObject));
    TextWriter tw = new StreamWriter(_location);
    serializer.Serialize(tw, obj);
    tw.Close();
}

Unfortunately it falls over on the first line with this message.

InvalidOperationException was unhandled: Unable to generate a temporary class (result=1). error CS0200: Property or indexer 'MyObject.Id' cannot be assigned to -- it is read only

If I set the Id property to public it works fine. Can someone tell me if I'm doing something, or at least if its even possible?

Upvotes: 77

Views: 73252

Answers (5)

ToolmakerSteve
ToolmakerSteve

Reputation: 21289

If you don't need a secure answer, one "good enough" hack is to have a public member, for the sake of serialization, with a name that discourages use in code elsewhere:

// The "real" member used by code. Tell serializer to ignore.
[XMLIgnore]
public Guid Id { get; private set; }
// This is for serializer. Could be named anything. But for humans reading the XML, have XML use the "real" name.
// Give it a member name "SERIALIZER_ONLY_Id" to "discourage" use.
[XmlElement(ElementName = "Id")]
public Guid SERIALIZER_ONLY_Id { get => Id; set => Id = value }

Upvotes: 0

Jerod Venema
Jerod Venema

Reputation: 44642

Its not possible with that particular serialization mode (see the other comments for workarounds). If you really want to leave your serialization mode as-is, you have to work around the framework limitations on this one. See this example

Esentially, mark the property public, but throw an exception if it's accessed at any time other than deserialization.

Upvotes: 0

Stefan Steinegger
Stefan Steinegger

Reputation: 64628

You could use the System.Runtime.Serialization.NetDataContractSerializer. It is more powerful and fixes some issues of the classic Xml Serializer.

Note that there are different attributes for this one.

[DataContract]
public class X
{
  [DataMember]
  public Guid Id { get; private set; }
}


NetDataContractSerializer serializer = new NetDataContractSerializer();
TextWriter tw = new StreamWriter(_location);
serializer.Serialize(tw, obj);

Edit:

Update based on Marc's comment: You should probably use System.Runtime.Serialization.DataContractSerializer for your case to get a clean XML. The rest of the code is the same.

Upvotes: 6

flalar
flalar

Reputation: 1221

Read only fields will not be serialized using the XmlSerializer, this is due to the nature of the readonly keyword

From MSDN:

The readonly keyword is a modifier that you can use on fields. When a field declaration includes a readonly modifier, assignments to the fields introduced by the declaration can only occur as part of the declaration or in a constructor in the same class.

So... you would pretty much need to set the fields value in the default constructor...

Upvotes: 2

Marc Gravell
Marc Gravell

Reputation: 1063198

You could use DataContractSerializer (but note you can't use xml attributes - only xml elements):

using System;
using System.Runtime.Serialization;
using System.Xml;
[DataContract]
class MyObject {
    public MyObject(Guid id) { this.id = id; }
    [DataMember(Name="Id")]
    private Guid id;
    public Guid Id { get {return id;}}
}
static class Program {
    static void Main() {
        var ser = new DataContractSerializer(typeof(MyObject));
        var obj = new MyObject(Guid.NewGuid());
        using(XmlWriter xw = XmlWriter.Create(Console.Out)) {
            ser.WriteObject(xw, obj);
        }
    }
}

Alternatively, you can implement IXmlSerializable and do everything yourself - but this works with XmlSerializer, at least.

Upvotes: 65

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