Is it possible to use a type loaded from string in a Generic Type factory?

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5.00/5 (2 votes)

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Hi,

I wrote a factory for some xml parser classes (one for each supplier). The parser classes implemented an interface and the factory would simply call the parser classes method. Here is my factory class:

C#

public static class FlightDataFactory<T> where T : Interface.IFlightDataWorker, new()
{
    public static FlightData.Model.Flight GetFlightData(string flightId)
    {
        T t = new T();
        return t.GetFlightData(flightId);
    }
    public static List<FlightData.Model.Flight> GetFlightData()
    {
        T t = new T();
        return t.GetFlightData();
    }
}

I hope that's all self explanatory.

I now need to load the classes from strings, kept in a db table of suppliers (The reason for this is that we will product-ize this system and only wish to include parsers that are relevant to that client).

I was creating the list of parser methods like this:

C#

private void InitializeWorkers()
{
    flightWorkers = new[]{
        new Worker.FlightServiceWorker(){
            Source = "AirNav",
            GetFlightByIdMethod = FlightData.Factory.FlightDataFactory<FlightData.Worker.AirNavWorker>.GetFlightData,
            GetFlightsMethod = FlightData.Factory.FlightDataFactory<FlightData.Worker.AirNavWorker>.GetFlightData
        },
        new Worker.FlightServiceWorker(){
            Source = "AirNavMock",
            GetFlightByIdMethod = FlightData.Factory.FlightDataFactory<FlightData.Worker.AirNavMockWorker>.GetFlightData,
            GetFlightsMethod = FlightData.Factory.FlightDataFactory<FlightData.Worker.AirNavMockWorker>.GetFlightData
        }
    };
}

My question is: Can I load the classes from a string in such a way as I can use them as types as in the above code, or must I invoke the methods instead.

If I have to invoke them then I guess my factory is a write off

Thanks. Please let me know if I can improve my question before down-voting it ^_^

Posted 20-Feb-15 1:19am

Andy Lanng

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CHill60 20-Feb-15 9:05am

Would Activator.CreateInstance be useful? https://msdn.microsoft.com/en-us/library/d133hta4(v=vs.110).aspx[^]

2 solutions

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Andy Lanng · Answer 1 · 2015-02-20T03:12:00

I solved this with a new (but not so neat) factory.

If anyone can help me tidy this up then I would be greatful

C#

   public delegate FlightData.Model.Flight GetFlightById(string flightId);
   public delegate List<flightdata.model.flight> GetFlights();
public static class FlightDataFactory
   {
       public static GetFlightById GetFlightByIdDataMethod(Type iFlightDataWorker)
       {
           if (!iFlightDataWorker.GetType().GetInterfaces().Contains(typeof(Interface.IFlightDataWorker)))
               throw new ArgumentException(string.Format("The type {0} does not implement the interface {1}.", iFlightDataWorker.Name, typeof(Interface.IFlightDataWorker).Name), "iFlightDataWorker");

           object worker = iFlightDataWorker.GetConstructor(Type.EmptyTypes).Invoke(new object[]{});

           return delegate(string flightId)
           {
               return (FlightData.Model.Flight)iFlightDataWorker.GetMethod("GetFlightData").InvokeWithExceptions(worker, new object[] { flightId });
           };

       }
       public static GetFlights GetFlightDataMethod(Type iFlightDataWorker)
       {
           if (!iFlightDataWorker.GetType().GetInterfaces().Contains(typeof(Interface.IFlightDataWorker)))
               throw new ArgumentException(string.Format("The type {0} does not implement the interface {1}.", iFlightDataWorker.Name, typeof(Interface.IFlightDataWorker).Name), "iFlightDataWorker");

           object worker = iFlightDataWorker.GetConstructor(Type.EmptyTypes).Invoke(new object[] { });

           return delegate
           {
               return (List<flightdata.model.flight>)iFlightDataWorker.GetMethod("GetFlightData").InvokeWithExceptions(worker, new object[] { });
           };
       }
   }</flightdata.model.flight></flightdata.model.flight>

I have also created a handy Extension method so I get past targetinvocationexceptions which I would hope not to get.

C#

public static object InvokeWithExceptions(this MethodInfo methodInfo, object obj, params object[] parameters)
{
    try
    {
        return methodInfo.Invoke(obj, parameters);
    }
    catch (TargetInvocationException exception)
    {
        if (exception.InnerException != null)
            throw exception.InnerException;
        throw;
    }
}

Matthew Dennis · Answer 2 · 2015-02-20T12:11:00

Solution 2

I think you would be better served by using a Dependency Injection or Inversion of Control Container such as Microsoft's Unity, NInject, StructureMap, or my Munq IocContainer.

You register the Interface implementations with the container and then either follow the Dependency Injection pattern or Service Locator pattern to get the implementation for the Interface when required.

Posted 20-Feb-15 12:11pm

Matthew Dennis

Comments

BillWoodruff 21-Feb-15 0:22am

I'm curious: how would that assist the OP to produce a different version Application for each client that included only the code for the XML parser designed for that client ?

Andy Lanng 23-Feb-15 5:36am

I too would like to know how I can implement this at run-time. Do you know of any articles? I have searched :S
Thanks