Dependency Injection in .NET with examples?

Question

Can someone explain dependency injection with a basic .NET example and provide a few links to .NET resources to extend on

Answer 1

Here's a common example. You need to log in your application. But, at design time, you're not sure if the client wants to log to a database, files, or the event log.

So, you want to use DI to defer that choice to one that can be configured by the client.

This is some pseudocode (roughly based on Unity):

You create a logging interface:

public interface ILog
{
  void Log(string text);
}

then use this interface in your classes

public class SomeClass
{
  [Dependency]
  public ILog Log {get;set;}
}

inject those dependencies at runtime

public class SomeClassFactory
{
  public SomeClass Create()
  {
    var result = new SomeClass();
    DependencyInjector.Inject(result);
    return result;
  }
}

and the instance is configured in app.config:

Now if you want to change the type of logger, you just go into the configuration and specify another type.