Runtime Overrides

Now let’s put the pieces together and see how we can override hard coded serialization attributes. Imagine our parking lot application sends updates about the parked cars to interested parties in an XML format. For some reason there is one client who needs the data in a slightly different format. Instead of writing an entire different set of classes to produce the custom format we simply customize the ones we already have to change the element names for ParkingLot and Car objects.

The example starts out by instantiating two XmlAttributes collections, one for the attributes for ParkingLot class, another one to apply attributes to the Cars field.

Next, we assign an XmlRootAttribute object to the XmlRoot property to change the root element name for ParkingLot objects.

Then we change the element name for a Car item in the Cars ArrayList to “ParkedCar” by assigning an XmlArrayItemAttribute to XmlArrayItems property.

Finally, we call the overloaded Add() method to add the two XmlAttributes objects to an XmlOverrides object.

Now the XmlOverrides object is set up and we can pass it to to the constructor of the XmlSerializer.

5           Listing 10.1: Serialization using attribute overrides

public static void SerializeCustomParkingLot(XmlWriter writer,

  ParkingLot parkingLot)

{

  XmlAttributes carsAttributes = new XmlAttributes();

  XmlAttributes classAttributes =
    new XmlAttributes();

  classAttributes.XmlRoot =
    new XmlRootAttribute("ParkingLotRoot");

 
  carsAttributes.XmlArrayItems.Add( new
    XmlArrayItemAttribute("ParkedCar", typeof(Car)));

  XmlAttributeOverrides overrides =
    new XmlAttributeOverrides();

  overrides.Add(typeof(ParkingLot), classAttributes);

  overrides.Add(typeof(ParkingLot), "Cars", carsAttributes);

  try

  {

    XmlSerializer xs = new XmlSerializer(
      typeof(ParkingLot), overrides );

     
    xs.Serialize( writer, parkingLot );

  }

  catch( InvalidOperationException ex )

  {

    System.Console.WriteLine( "Bad override attributes" );

  }

}

The output of the Serialize() method (Listing 10.2) shows that XML nodes corresponding to items in the ArrayList “Cars” are now named “ParkedCar” as specified by the XmlArrayItem attribute. The XmlRootAttribute applied to the ParkingLot class changes the name of the root node from ParkingLot to “ParkingLotRoot”.

6           Listing 10.2: A serialized ParkingLot object with and without the overriding attributes from Listing 10.1