Unity Singleton Code

Question

I'm new to Unity and am trying to write some Unity logic which initialises and register/resolves a singleton instance of the Email object so that it can be used across several other objects, one example below being OperationEntity.

So when it's registered it populates the Email singleton with some values from a config file, then whenever an instance of OperationEntity is created (in my case it's being deserialized) it uses that same Email singleton. So all my client logic needs to do is deserialize OperationEntity and call PerformAction() - with the email instance taken care of by Unity.

public interface IEmail
{
    string FromName { get; set; }
    string FromEmailAddress { get; set; }
}

public class Email : IEmail
{
    public string FromName { get; set; }
    public string FromEmailAddress { get; set; }

    public Email(string fromName, string fromEmailAddress)
    {
        FromName = fromName;
        FromEmailAddress = fromEmailAddress;
    }
}

public class OperationEntity
{
    private readonly IEmail _email;

    public int OperationId { get; set; }
    public string OperationName { get; set; }
    public string ToAddress { get; set; }

    public OperationEntity(IEmail email)
    {
        _email = email;
    }

    public void PerformAction()
    {
        _email.ToAddress = ToAddress;
        _email.Body = "Some email body";
        _email.Deliver();
    }
}

Any help would be appreciated in getting this Unity code to work

    public static void Register(IUnityContainer container)
    {
        container
            .RegisterType<IEmail, Email>(
            new InjectionFactory(c => new Email(
                "To Name", 
                "to@email.com")));

        var email = container.Resolve<IEmail>();  

        container.RegisterType<OperationEntity>(
            "email", new ContainerControlledLifetimeManager(),
            new InjectionConstructor(email));
    }

Answer 1

First, you need a proper lifetime manager the ContainerControlledLifetimeManager is for singletons.

For custom initialization, you could probably use InjectionFactory

This lets you write any code which initializes the entity.

Edit1: this should help

public static void Register(IUnityContainer container)
{
    container
        .RegisterType<IEmail, Email>(
        new ContainerControlledLifetimeManager(),
        new InjectionFactory(c => new Email(
            "To Name", 
            "to@email.com")));
}

and then

var opEntity = container.Resolve<OperationEntity>();

Edit2: To support serialization, you'd have to rebuild dependencies after you deserialize:

public class OperationEntity
{
   // make it public and mark as dependency   
   [Dependency]
   public IEmail _email { get; set;}

}

and then

OperationEntity entity = somehowdeserializeit;

// let unity rebuild your dependencies
container.BuildUp( entity );

Answer 2

You could use:

container.RegisterType<IEmail, Email>(new ContainerControlledLifetimeManager());

Answer 3

If IEmail is a singleton with no dependencies (just custom arguments), you can new it up yourself:

container.RegisterInstance<IEmail>(new Email("To Name", "to@email.com"));

That will register the supplied instance as a singleton for the container.

Then you just resolve the service:

container.Resolve<OperationEntity>();

And because you are resolving a concrete type, there is no registration required. Nevertheless, if you would like that service to also be a singleton, you can register it using ContainerControlledLifetimeManager and then all calls to resolve (or when injecting it as a dependency to another class) will return the same instance:

container.RegisterType<OperationEntity>(new ContainerControlledLifetimeManager());