Question

How can you get castle Windsor to choose the right implantation of a interface at run time when you have multiple implementations in the container.

For example lets say i have a simple interface called IExamCalc that does calculations to work out how someone did in that exam.

No we have several implementation of this like bellow for example,

public interface IExamCalc {     int CalculateMark(ExamAnswers examAnswers) }  public class WritenExam : IExamCalc {     public int CalculateMark(ExamAnswers examAnswers)     {          return 4;     } }  public class OralExam : IExamCalc {     public int CalculateMark(ExamAnswers examAnswers)     {          return 8;     } }  public class ExamMarkService {     private IExamCalc _examCalc;     public ExamMarkService(IExamCalc examCalc)     {         _examCalc = examCalc;     }      public int[] CalculateExamMarks(ExamAnswers[] examAnswers)     {         IList<int> marks = new List<int>;         foreach(ExamAnswers examanswer in examaAnswers)         {             marks.Add(_examCalc.CalculateMark);         }     } } 

Say the ExamMarkService is being resloved through Windor how can i make sure that the correct implementation is injected in the constructor and is this an example of a multi-tenancy problem?

Hope that all makes sence

Colin G

Answer 1

As David said, you can’t, but IHandlerSelector will let you take control. Check out the tests to get an idea of how to use them: https://svn.castleproject.org/svn/castle/trunk/InversionOfControl/Castle.Windsor.Tests/HandlerSelectorsTestCase.cs

Basically, you would do something like:

public class WritenExamHandler : IHandlerSelector     {         public bool HasOpinionAbout(string key, Type service)         {             // Decision logic here             return somethingThatWouldBeTrueToSelectWritenExam && service == typeof(IExamCalc);         }          public IHandler SelectHandler(string key, Type service, IHandler[] handlers)         {             return handlers.Where(handler => handler.ComponentModel.Implementation == typeof (WritenExam)).First();         }     } 

and then you register it with:

container.Kernel.AddHandlerSelector(new WritenExamHandler()); 

This will allow you to easily deal with multi-tenency issues 🙂