README.md

MvvmCross with MediatR

I started using MediatR a while ago but didn't get into the full benefits of the MediatR library. Last week I decided to give it a try but found out it was much harder than I thought. All samples of the library are working with different kind of IoC container frameworks but not with MvvmCross.

After debugging the MediatR source we found out that (at least autofac but since other frameworks work too I guess they do the same) return an empty array when a Type cannot be resolved.

From the source:

return serviceFactory
                .GetInstances<IPipelineBehavior<TRequest, TResponse>>()
                .Reverse()
                .Aggregate((RequestHandlerDelegate<TResponse>) Handler, (next, pipeline) => () => pipeline.Handle((TRequest)request, cancellationToken, next))();

After splitting it to debug:

var test1 = serviceFactory.GetInstances<IPipelineBehavior<TRequest, TResponse>>();

            var test2 = test1.Reverse();

            var test3 = test2.Aggregate((RequestHandlerDelegate<TResponse>)Handler, (next, pipeline) => () => pipeline.Handle((TRequest)request, cancellationToken, next))();

            return test3;

With MvvmCross test1 throws an exception:

{MvvmCross.Exceptions.MvxIoCResolveException: Failed to resolve type System.Collections.Generic.IEnumerable`1[[MediatR.IPipelineBehavior`2[[MediatR.Examples.Ping, MediatR.Examples, Version=5.1.0.0, Culture=neutral, PublicKeyToken=null],[MediatR.Examples.Pong, MediatR.Examples, Version=5.1.0.0, Culture=neutral, PublicKeyToken=null]], MediatR, Version=5.1.0.0, Culture=neutral, PublicKeyToken=null]]    at MvvmCross.IoC.MvxIoCContainer.Resolve(Type t) in C:\projects\mvvmcross\MvvmCross\IoC\MvxIoCContainer.cs:line 246    at MediatR.Examples.MvvmCross.UnitTest1.<>c.<Test1>b__0_0(Type serviceType) in /Users/jacob.duijzer/Downloads/MediatR-5.1.0/samples/MediatR.Examples.MvvmCross/UnitTest1.cs:line 34}

While AutoFac returns:

{MediatR.IPipelineBehavior<MediatR.Examples.Ping, MediatR.Examples.Pong>[0]}

My current work-around it this:

Mvx.RegisterSingleton<ServiceFactory>((Type serviceType) =>
{
    var resolver = Mvx.Resolve<IMvxIoCProvider>();

    try
    {
        return resolver.Resolve(serviceType);
    }
    catch (Exception)
    {
        // a "bit" buggy, I know!
        return Array.CreateInstance(serviceType.GenericTypeArguments[0], 0);
    }
});

I know it is buggy code but I ran out of time for now and just want to share my experiences. Hopefully I will jump back into it in a while.

MvvmCross

MediatR