C# inheritance XmlSerializer

Question

greetngs,

i have two classes:

[Serializable]
public class FireGridUnit
{
    public GridUnit FireGridLocation { get; set; }

}

[Serializable]
public class FireResult: FireGridUnit
{
    public bool Hit { get; set; }

    public bool ShipDestroyed { get; set; }

    public Ship.ValidShips DestroyedShipType {get; set;}

    public bool Win { get; set; }
}

as you see FireResult inherits FireGrdUnit.

in my code when i try to use them i get a runtime error:

Unable to cast object of type 'NietzscheBattleships.FireGridUnit' to type 'NietzscheBattleships.FireResult'.

is this because if i am serializing the class has to be independant ie not be inherited?

many thanks.

EDIT:

it happens here:

                    XmlSerializer ss;
                    StringWriter ww;

                    ss = new XmlSerializer(typeof(FireResult));
                    ww = new StringWriter();

                    ss.Serialize(ww, fireGridUnit);

                    MessageBox.Show("hello");

                    MessageBox.Show(ww.ToString());

it gives the error mentioned. if i take this out then it runs but obviously not doing what want it to do.

EDIT: i got it my mistake!

ss.Serialize(ww, fireGridUnit); should be ss.Serialize(ww, fireResult);

thanks.

Please provide the code where you are using these classes.

Sandor Drieënhuizen
– Sandor Drieënhuizen

2010-03-22 16:34:35 +00:00
Commented Mar 22, 2010 at 16:34 — Sandor Drieënhuizen
– Sandor Drieënhuizen, Commented Mar 22, 2010 at 16:34
i would but the actual code is rather long.

iTEgg
– iTEgg

2010-03-22 16:37:24 +00:00
Commented Mar 22, 2010 at 16:37 — iTEgg
– iTEgg, Commented Mar 22, 2010 at 16:37
When does it happen ? when you deserialize ?

Thomas Levesque
– Thomas Levesque

2010-03-22 16:40:35 +00:00
Commented Mar 22, 2010 at 16:40 — Thomas Levesque
– Thomas Levesque, Commented Mar 22, 2010 at 16:40

Marc Gravell · Accepted Answer · 2010-03-22 16:39:45Z

4

The [Serializable] does nothing here (XmlSerializer doesn't care); assuming the real problem is in the serialization API (not just the cast), then:

[XmlInclude(typeof(FireResult))]
public class FireGridUnit {...}

Then to use it, something like:

        XmlSerializer ser = new XmlSerializer(typeof(FireGridUnit));
        using (MemoryStream ms = new MemoryStream())
        {
            ser.Serialize(ms, new FireResult { Hit = true });
            ms.Position = 0;
            FireGridUnit fr = (FireGridUnit)ser.Deserialize(ms);
            Debug.WriteLine(fr is FireResult); // true
        }

answered Mar 22, 2010 at 16:39

Marc Gravell

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1 Comment

Sandor Drieënhuizen Over a year ago

Now how about that. Very interesting attribute, could have saved the day if I had read this two years ago :)

Anzurio · Accepted Answer · 2010-03-22 16:42:17Z

2

No, it has nothing to do with [Serializable]. The way polymorphism works is the other way around. You can only upcast ((ParentClass)childObject;) through the hierarchy and not downcast ((ChildClass)parentObject).

For instance:

//This is correct
FireResult result = new FireResult();
FireGridUnit unit = result;

//This just does not seem right
FireGridUnit unit = new FireGridUnit();
FireResult result = unit;

EDIT: Think of inheritance the following way. All FireResults are FireGridUnits, as such, you can convert FireResults to FireGridUnits. However, not all FireGridUnits are FireResult because, you could have a third class that inherits from FireGridUnit. As such, you can not convert ALL FireGridUnits to a FireResult.

edited Mar 22, 2010 at 16:42

answered Mar 22, 2010 at 16:36

Anzurio

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Comments

Hans Passant · Accepted Answer · 2010-03-22 16:40:07Z

1

Nope, you can't down-cast a FireGridUnit to a FireResult. The other way around is fine. Either you serialized the wrong object or the cast you used on the return value of Deserialize() is wrong.

answered Mar 22, 2010 at 16:40

Hans Passant

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