Add information about working in applications that lack Ambient Context

[dotnetjunkie]

A typical way of working with Simple Injector in Ambient Context-lacking applications (Read: Windows RT) is the following:

// Starting/ending scopes
using (var scope = new Scope(container))
{
    // Attach runtime data to the scope to allow it to flow through the graph
    scope.SetItem("requestId", Guid.NewGuid());

    // Resolve directly from the scope:
    var service = scope.GetInstance<IMyService>();
    await service.DoYourThing();
}

// Using scopes
public class CommandDispatcher : ICommandDispatcher
{
    private readonly Scope scope;
    public CommandDispatcher(Scope scope) {
        this.scope = scope;
    }

    public void Dispatch<T>(T command) {
        // Services should again be resolved from the scope to continue flowing runtime data.
        var handler = this.scope.GetInstance<ICommandHandler<T>>();

        handler.Handle(new CommandEnvelope<T>(
            // Runtime data can be retrieved from the Scope again by injecting it into an adapter:
            requestId: (Guid)this.scope.GetItem("requestId"),
            command: command));
    }
}

The previous code enables flowing runtime data; in case components must be registered as scoped, a custom scoped lifestyle must be created (since Simple Injector doesn't have anything for this in the box):

sealed class NonAmbientScopedLifestyle : ScopedLifestyle
{
    public NonAmbientScopedLifestyle() : base("Non-ambient Scoped") { }

    protected override Func<Scope> CreateCurrentScopeProvider(Container c) {
        return ThrowNotSupported;
    }

    [DebuggerStepThrough] private static Scope ThrowNotSupported()  {
        throw new NotSupportedException("You can't resolve directly from the container.");
    }
}

// Registration
var container = new Container();
container.Options.DefaultScopedLifestyle = new NonAmbientScopedLifestyle();

container.Register<IUserContext, UserContext>(Lifestyle.Scoped);

[dotnetjunkie]

Feature will be removed from v4.