Question

I like the idea of extending on the client side classes that are data contracts of WCF services using partial classes. But I encountered a problem that considerably spoils the party.

Imagine on the server side I have a class:

[DataContract]
public class SolidObject
{
    [DataMember]
    public Point Position { get; set; }
    [DataMember]
    public Size Size { get; set; }
}

On the client side I have a proxy class generated, which is used there in the business logic layer. According to the needs of the business logic I extend it this way:

public partial class SolidObject
{
    public Rect Bounds { get { return new Rect(Position.X - Size.Width / 2, Position.Y - Size.Height / 2, Size.Width, Size.Height); }}
}

Now I want to ensure that anytime either Position or Size changes, then Bounds chage event is invoked. It is easy to do by the code:

PropertyChanged += (sender, e) =>
    {
        if ((e.PropertyName == "Position") || (e.PropertyName == "Size")) PropertyChanged.Invoke(this, new PropertyChangedEventArgs("Bounds"));
    };

The question is where the good place to put this code in is.

If objects weren’t created by a service call, I’d put it into the constructor. But WCF services ignore constructors on the client side, see constructor not showing up in my WCF client, serialization problem?.

Now, right after service response my program searches through data contract hierarchy, gets desired objects and adds event handlers. But I don’t think it’s a right thing.

So I’m interesting in where to it is better to do or, maybe, reasoning that the whole approach should be changed. Any ideas appreciated.

Answer 1

You could use the [OnDeserlialized] attribute to insert a method that gets called after deserizlization.

public partial class SolidObject
{
    public Rect Bounds
    {
        get
        {
            return new Rect(Position.X - Size.Width / 2, Position.Y - Size.Height / 2, Size.Width, Size.Height);
        }
    }

    [OnDeserialized]
    public void Initialize(StreamingContext streamingContext)
    {
        PropertyChanged += (sender, e) =>
        {
            if ((e.PropertyName == "Position") || (e.PropertyName == "Size"))
                PropertyChanged.Invoke(this, new PropertyChangedEventArgs("Bounds"));
        };
    }
}