C# Unity - Dynamically resolve Registered Type

Question

I have a scenario where we are receiving in xml messages. I need to look at the header of the message to determine what message type / version it is (coming from legacy system). I would like to be able to Register the message types Then pass in a param to resolve the specific type. I am new to DI / Unity (If you haven't noticed) so I might be trying to apply a bad practice or approaching this incorrectly. Want to move a way from an existing factory pattern we are utilizing to accomplish this.

This obviously works:

    XDocument xml = XDocument.Load(@"D:\Demos\XmlMessages\AllMessages\LogEvent.xml");
    var container = new UnityContainer();

    //Base Works
    container.RegisterType<IMessage, LogEvent>(new InjectionProperty("XmlDoc", xml));
    var baseMessage = container.Resolve<BaseMessage>();
    baseMessage.ParseDocument();

Not sure how to apply dynamic resolution here?:

XDocument xml = XDocument.Load(@"D:\Demos\XmlMessages\AllMessages\LogEvent.xml");
var container = new UnityContainer();
    container.RegisterType<IMessage, LogEvent>("LogEvent", new InjectionProperty("XmlDoc", xml));
    var baseMessage = container.Resolve(typeof(IMessage), "LogEvent");

    baseMessage.ParseDocument(); //Just returning type so obviously can't run this

Is registering my messages the right approach? If so then how can I accomplish resolving to my BaseMessage so I can call ParseDocument?

Any info / suggestions greatly appreciated.

EDIT: I already have a class that will parse the header of the XML and feed me the version and type (So for instance it will tell me that this is a "LogEvent" message). That is why I was considering utilizing DI is that I could simply pass the parsed value ( in this case "LogEvent" to the Resolver. Just wanted to update based on Sebastian's response. Even if this scenario is not applicable and I should stick with the factory method. I would like to understand how this type of dynamic call would be possible.

Thanks,

S

You may find this relevant: blog.ploeh.dk/2011/09/19/…

Mark Seemann
– Mark Seemann

2012-01-25 21:37:23 +00:00
Commented Jan 25, 2012 at 21:37 — Mark Seemann
– Mark Seemann, Commented Jan 25, 2012 at 21:37

Sebastian Weber · Accepted Answer · 2012-01-25 21:33:10Z

2

I would recommend that you stick with the factory. A DI container is not a factory for business objects but a tool that helps you compose loosely coupled applications.

You can inject the factory into those classes that need to handle incoming messages. But don't try to put the logic that figures out what to do with the XML into the container.

Update

If you already have a mechanism to get the concrete Type of the message object you could either use a simple call to Activator.CreateInstance and ignore Unity completely.

Or, given that you have an instance of the container available, call

object msg = container.Resolve(typeof(LogEvent));

This method returns an object. If you know that you would get an instance of some base class you can cast it to that Type.

If the message Type is a concrete class (not an interface or abstract class) Unity will figure out how to create an instance of that Type.

edited Jan 25, 2012 at 21:33

answered Jan 25, 2012 at 18:37

Sebastian Weber

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2 Comments

scarpacci Over a year ago

Thanks @SebastianWeber....take a look at my edit. Just wanted to get your input

scarpacci Over a year ago

That is actually what I am currently doing is using Reflection to call "Activator.CreateInstance". I will take a look at your object example above. Thanks Sebastion.

scarpacci · Accepted Answer · 2012-01-26 01:42:50Z

0

Here is what I had to do to resolve the issue. This works:

Get Xml and Define Container:

XDocument xml = XDocument.Load(@"D:\Demos\XmlMessages\AllMessages\LogEvent.xml");
var container = new UnityContainer();

Register:

container.RegisterType<IMessage, LogEvent>("LogEvent", new InjectionProperty("XmlDoc", xml));

Resolve by Registered Name(The resolve portion below is what I was doing wrong)

  var baseMessage = container.Resolve<IMessage>("LogEvent");
    baseMessage.ParseDocument();

answered Jan 26, 2012 at 1:42

scarpacci

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