MediatR

MediatR

MediatR is a low-ambition library trying to solve a simple problem — decoupling the in-process sending of messages from handling messages. Cross-platform, supporting .NET Framework 4.6.1 and netstandard2.0.

Setup

Install the package via NuGet first: Install-Package MediatR

MediatR has no dependencies. You will need to configure a single factory delegate, used to instantiate all handlers, pipeline behaviors, and pre/post-processors.

You will need to configure two dependencies: first, the mediator itself. The other dependency is the factory delegate, ServiceFactory. The Mediator class is defined as:

public class Mediator : IMediator
{
    public Mediator(ServiceFactory serviceFactory)
}

The factory delegates are named delegates around a couple of generic factory methods:

public delegate object ServiceFactory(Type serviceType);

Declare whatever flavor of handler you need - sync, async or cancellable async. From the IMediator side, the interface is async-only, designed for modern hosts.

Finally, you'll need to register your handlers in your container of choice.

Autofac

https://github.com/jbogard/MediatR/blob/master/samples/MediatR.Examples.Autofac/Program.cs

The full example looks like:

// Uncomment to enable polymorphic dispatching of requests, but note that
// this will conflict with generic pipeline behaviors
// builder.RegisterSource(new ContravariantRegistrationSource());

// Mediator itself
builder
    .RegisterType<Mediator>()
    .As<IMediator>()
    .InstancePerLifetimeScope();

// request & notification handlers
builder.Register<ServiceFactory>(context =>
{
    var c = context.Resolve<IComponentContext>();
    return t => c.Resolve(t);
});

// finally register our custom code (individually, or via assembly scanning)
// - requests & handlers as transient, i.e. InstancePerDependency()
// - pre/post-processors as scoped/per-request, i.e. InstancePerLifetimeScope()
// - behaviors as transient, i.e. InstancePerDependency()
builder.RegisterAssemblyTypes(typeof(MyType).GetTypeInfo().Assembly).AsImplementedInterfaces(); // via assembly scan
//builder.RegisterType<MyHandler>().AsImplementedInterfaces().InstancePerDependency(); 

Basics

MediatR has two kinds of messages it dispatches:

• Request/response messages, dispatched to a single handler
• Notification messages, dispatched to multiple handlers