XmlSerializer.Serialize ambiguous

Question

I have create testing application that has 3 classes - Car - Radio - SportCar : Car (has a Radio) As the serialize process when I create instance of XmlSerializer object I use 2 object to testing ``` XmlSerializer xmlSerializer = new XmlSerializer(typeof(SportCar)); ``` and ``` XmlSerializer xmlSerializer = new XmlSerializer( typeof(SportCar), new Type[] { typeof(Car), typeof(Radio) }); ``` The result of this 2 approach is identical, so I want to know what is the difference between these 2 constructor or critical point that need to use #2 constructor?

Accepted Answer

The big difference is when you need to tell `XmlSerializer` about sub classes - for example:

```
XmlSerializer xmlSerializer = new XmlSerializer(typeof(Car),
     new Type[] { typeof(SportCar), typeof(Radio) });
```

Here, without the extra info if wouldn't have known (just from `Car`) about either `SportCar` or `Radio` - so if you give it a object that is actually a `SportCar`, it would fail:

```
Car car = new SportCar {...};
xmlSerializer.Serialize(destination, car);
```

You can also do this by setting `[XmlInclude(typeof(SportCar))]` against the `Car` type definition:

```
[XmlInclude(typeof(SportCar))]
public class Car {...}
```

This is easier, but is only possible if the `Car` type is in an assembly that knows about `SportCar`. But you often do know this, so `XmlInclude` is the preferred option.

Additionally: there are some efficiency benefits of `XmlInclude`; behind the scenes the system uses dynamic type generation to make `XmlSerializer` efficient. For this reason, you should generally keep hold of (and re-use) the `XmlSerializer` instance you create; for example, by storing it in a static field. However, the system does this automatically for the default usage (`new XmlSerializer(typeof(Car))`) - i.e. no matter how many times you use this constructor, it only generates the dynamic code once. If you use the more complex constructor (`new XmlSerializer(typeof(Car),new Type[] { typeof(SportCar), typeof(Radio) })`) it will do the type generation each time.

XmlSerializer.Serialize ambiguous

Solution

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