Sunday, April 06, 2008

Xaml, the ultra lightweight IOC container

I've been testing xaml for defining what object to create at runtime. Although xaml is often linked to windows workflow foundation or windows presentation foundation, it can easily be applied to your own domain.

Xaml is a xml language where you can define how a .net object structure is to be initialized. It has many similarities to, lightweight IOC.

The greatest thing about Xaml is it's very easy syntax. Every node in your xml is giveng the name of the class to instantiate. By givin the root node a namespace, your VS.Net provides full intellisense to what properties are on what classes and what type they are. By making typeconverters for your classes you are able to provide a simple way of creating your simple classes.

What is missing then? Well... Xaml is just a language that enables you to create objects. Because of this it doesn't give you the means of controlling the lifespan of your objects. You can't state that an object should be a singleton for the application etc. If you want that you have to code it yourselfes.

Xaml supports property injection but not constructor injection which means all properties needs a public setter for it to be set by Xaml. Most of my properties already have public setters, but I have to alter a few for them to be xaml enabled.

Another thing I'm missing is the support for generic types. In xaml you cannot instansiate List as an example. In stead you kan implement some xaml interfaces or you will have to make new classes that inherrit from the generic type you want.


I have used my search criteria framework that I introduced in "A use for operator overloading" for testing the Xaml.

The above xaml creates the object structure ressembling the following query: Content = "teste feste" or Title = "teste feste" or (Content="test" and Title="test")

I would also have liked a possibility to cross reference objects (create it once and reuse it multiple places in my xaml), but overall xaml provides a very simple way of creating your object away from your code. Whereas has quite a heavy syntax xaml is very intuitive and will be comprehendable, even for people with no technical background.

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