Serialize an object that has an interface

Question

I'm having quite the problem with my XML serialization issue. I've been working on my project to (de) serialize an object that has an interface as an attribute. I know that you can't serialize an interface and that is what my error tells me.

Here is an example of the object that I want to save to a file:

public class Task
{
    public int id;
    public string name;
    public TypeEntree typeEntree;
    public int idRequired;
    public string code;
    public int waitTime;
    public string nameApp;
    // ... Constructors (empty and non-empty) and methods ...
}

TypeEntree is an empty interface, it's only to relate different objects and use them easily around my application. For instance, here are two of the objects that uses this interface:

[Serializable]
public class Mouse : TypeEntree
{
    public Point point;
    public IntPtr gaucheOuDroite;
    public string image;
    // ... Constructors (empty and non-empty) and methods ...
}

[Serializable]
public class Sequence : TypeEntree
{
    public List<Tuple<string, Point, long, IntPtr>> actions;
    // ... Constructors (empty and non-empty) and methods ...
}

The interface TypeEntree also has the [Serializable] attribute and also the [XmlInclude (typeof (Mouse)] for each of my classes that uses this interface.

Here is my question: Why does when I try to serialize, it cannot detects the type of my object (typeEntree in Task) since I added the [XmlInclude (typeof (Mouse)] attributes?

Also, how should I fix this issue?

Additionnally, here are the methods of serializing/deserializing I found that seems to works very well without interface: https://stackoverflow.com/a/22417240/6303528

In the last sentence I specify it. http://stackoverflow.com/a/22417240/6303528 - XML XmlSerializer — SacDeFromage, May 07 '16 at 10:36
The serializer add the attributes not for serializing, but fore de-serializing. The net library need the attributes when deserializing to distinguish between the inherited classes. — jdweng, May 07 '16 at 14:52
You can't serialize an interface with `XmlSerializer` even if you add `XmlInclude`. See [XML serialization of interface property](https://stackoverflow.com/questions/1333864) or [Serializing interfaces](https://stackoverflow.com/questions/4659248). [`XmlInclude`](https://msdn.microsoft.com/en-us/library/system.xml.serialization.xmlincludeattribute.aspx) is for base class/derived class hierarchies. — dbc, May 07 '16 at 18:12
Incidentally, if I change `TypeEntree` to be a `public abstract class`, your types still can't be serialized because `IntPtr` can't be serialized directly. As a workaround you could use a `long` proxy property. See [Serialize an IntPtr using XmlSerializer](https://stackoverflow.com/questions/3472509/serialize-an-intptr-using-xmlserializer). — dbc, May 07 '16 at 18:15
Thank you for your links, I'll be working on it and updating soon. @dbc — SacDeFromage, May 07 '16 at 21:32
Watch out for `Tuple` as well. See [Why I could not serialize a tuple in C#?](https://stackoverflow.com/questions/13739348/why-i-could-not-serialize-a-tuple-in-c) and [Tuple cannot be serialized because it does not have a parameterless constructor](https://stackoverflow.com/questions/33225824) — dbc, May 07 '16 at 21:41
Thank you for your help, It was actually related to everything you said! I'll do a response to update what I had wrong and how I fixed it. Thank you so much, it's working now :). I still have to figure out how to deserialize it, but it's a huge chunk! @dbc — SacDeFromage, May 07 '16 at 22:05

score 1 · Accepted Answer · edited May 23 '17 at 10:28

Thanks to @dbc links in the comments of my first questions, I was able to figure out every problem. Here is what I did :

My interface TypeEntree became an abstract class.

[Serializable]
[XmlInclude(typeof(Mouse))]
[XmlInclude(typeof(Keyboard))]
[XmlInclude(typeof(Sequence))]
public abstract class TypeEntree
{
}

Also, the Mouse class had an IntPtr, which is not serializable. I had to convert it to an Int64 (a long). Source is both from @dbc comments and here : Serialize an IntPtr using XmlSerializer

Finally, a Tuple cannot be serialized since it does not have a parameterless constructor. A fix to this is simply change the type of the Tuple to the class I created (TupleModifier) following this example : https://stackoverflow.com/a/13739409/6303528

public class TupleModifier<T1, T2, T3, T4>
{
    public T1 Item1 { get; set; }
    public T2 Item2 { get; set; }
    public T3 Item3 { get; set; }
    public T4 Item4 { get; set; }

    public TupleModifier() { }

    public static implicit operator TupleModifier<T1, T2, T3, T4>(Tuple<T1, T2, T3, T4> t)
    {
        return new TupleModifier<T1, T2, T3, T4>()
        {
            Item1 = t.Item1,
            Item2 = t.Item2,
            Item3 = t.Item3,
            Item4 = t.Item4
        };
    }

    public static implicit operator Tuple<T1, T2, T3, T4>(TupleModifier<T1, T2, T3, T4> t)
    {
        return Tuple.Create(t.Item1, t.Item2, t.Item3, t.Item4);
    }
}

and to use it in the Sequence class like it was used :

public List<TupleModifier<string, Point, long, long>> actions;

Serialize an object that has an interface

1 Answers1