Inversion of Control & Dependency Injection in the .NET Framework

Question

Is there any specific example/instance of DI being applied as an architectural principle or design pattern in the .NET Framework itself? Do any (or many) of the types in the framework/BCL conform to IoC?

The type names and a brief illustration/explanation based in C# would be great!

This would compund the need for DI infused design principle as a best-practice...as it is gleaned from the base framework itself.

I reiterate, I am not looking for IoC/DI Frameworks BUT for IoC/DI IN the framework.

EDIT: Just wanted to get more instances/examples ... hence the bounty!

Answer 1

In general there aren't a lot of examples of DI in the BCL - perhaps because the BCL is a rather self-contained framework, and DI is more of an application architecture concern... However, here are some examples I've been able to find so far.

Constructor Injection

There are not many examples of Constructor Injection in the BCL. The best candidates are

• System.IO.StreamWriter
• System.IO.StreamReader

Property Injection

• System.ComponentModel.IComponent.Site

We also see a variation in Workflow Foundation's WorkflowRuntime.AddService and related methods, although you might argue that this is closer to Method Injection.

Method Injection

• System.ComponentModel.Design.IDesigner.Initialize
• System.ComponentModel.TypeConverter (many methods take ITypeDescriptorContext)
• System.Web.Mvc.IModelBinder.BindModel (from ASP.NET MVC)

Ambient Context

• System.Threading.Thread.CurrentPrincipal
• System.Threading.Thread.CurrentCulture
• System.Threading.Thread.CurrentUICulture
• System.Diagnostics.Trace.Listeners

FWIW, I drew these examples from my upcoming book.

Answer 2

Both the StreamReader and StreamWriter could be seen as examples of IoC/DI.

Each allow you to inject a different Stream object (or one of its derivatives) for reading/writing respectively.

FileInfo fi = new FileInfo(@"C:\MyFile.dat");
StreamWriter sw = new StreamWriter(fi.Open());

Or:

MemoryStream ms = new MemoryStream();
StreamWriter sw = new StreamWriter(ms);

Would both allow:

sw.Write("Hello world!");

The same way, no matter what kind of Stream you injected in the call to the constructor.