How to implement Factory Interface in Simple Injector With Parameters

Question

This answer shows how to resolve instances using a factory interfaces without parameters.

I am using the following code

public interface ISimpleBarFactory 
{
   Bar CreateBar(int value);
}

public sealed class SimpleBarFactory : ISimpleBarFactory 
{
    private readonly Container _container;
    public SimpleBarFactory (Container container)
    {
        _container = container;
    }

    public Bar CreateBar(int value) 
    {
       _container.Register(() => new Bar(vlue));
       return _container.GetInstance<Bar>();
    }
}

to resolve instances which have constructor parameters.

However, I get the following exception when using the factory to instantiate the service class:

The container can't be changed after the first call to GetInstance, GetAllInstances and Verify.

Which is the right way of to resolve instances using factory interfaces with parameters?

Update

The following is my code. I am migrating the code from Ninject.

public interface IFormsUIFactory
{
   AccountUI CreateAccountUI(Account account);
}

public class FormsUIFactory
{
    private readonly IFormsUIFactory _uiFactory;
    public FormsUIFactory(IFormsUIFactory uiFactory)
    {
        _uiFactory = uiFactory;
    }

    public void CreateAccountUI(Account account)
    {
        _uiFactory.CreateAccountUI(account);
    }
}

UI class to be injected

public partial class AccountUI : Form
{
    private readonly IAccountMaintenanceProcessor _processor;
    private readonly Account _account;
    public AccountUI(IAccountMaintenanceProcessor accountProcessor, Account account)
    {      
        _processor = accountProcessor;
        _account = account;
    }

 }

Instantiating code:

var account = new Account();
// Populate values for the account

var frm = _uiFactory.CreateAccountUI(account);

The point is you should register `Bar` only **once** at application startup. And use something like resolving with dynamic parameters to pass in `value`. You need to tell what IoC are you using because every IoC has different ways (syntaxes) — Khanh TO, Jul 20 '15 at 13:15
Your example is too abstract. Please update your question to show the real type names and code of what you want to do. The reason I'm asking this is because you sre mixing runtime data with dependencies, and this is bad. But if you show your actual application design, we will be able to give some feedback on that. — Steven, Jul 20 '15 at 14:12

Steven · Accepted Answer · 2016-03-11T11:25:19.397

The problem you are having is caused by the fact that you are mixing runtime data (your Account) object, with components. You DI container is in charge of building object graphs of components. Those components should typically be stateless and runtime data should flow through the object graphs using method calls. Injecting runtime data in constructors of your components, makes those components statefull and complicates your application in many different ways; you are witnessing one of those complications today. But there are many of downsides of doing this. For instance, injecting runtime data into the constructor makes it impossible to verify your object graph (using an automated test) and makes it easy for your application to break at runtime. So this in no way Simple Injector specific, but Simple does make the problem more eminent by not allowing to passing in runtime values when resolving services. You can find a detailed explanation about this here.

So instead, try to keep your components as stateless as possible and at least keep runtime data out of the constructor. A simple way to achieve this is to add a property to the form that allows setting the entity you are working with. A generic interface can be added to a form to allow this:

interface IForm<TEntity>
{
    TEntity Entity { get; set; }
}

This generic interface can be used in the IFormFactory abstraction:

interface IFormFactory
{
    TForm CreateFormFor<TForm, TEntity>(TEntity entity) 
        where TForm : Form, IForm<TEntity>;
}

Creating an implementation for IFormFactory is as easy as this:

public class FormFactory : IFormFactory
{
    private readonly Container container;

    public FormFactory(Container container) {
        this.container = container;
    }

    public TForm CreateFormFor<TForm, TEntity>(TEntity entity) 
        where TForm : Form, IForm<TEntity> {
        var form = this.container.GetInstance<TForm>();
        form.Entity = entity;
        return form;
    }
}

Thank you for the assistance and clarification. I never realized that injecting runtime data had so many downsides. — kagundajm, Jul 21 '15 at 21:48

How to implement Factory Interface in Simple Injector With Parameters

1 Answers1