Using Microsoft Unity IOC, how can you pass it an existing object to inject?

Question

So if I have:

public class CustomerViewModel
{
    public CustomerViewModel(ICustomer customer)
    {
        this.customer = customer
    }
}

then is there a way to achieve:

ICustomerViewModel customerViewModel = container.Resolve<ICustomerViewModel>(existingCustomer);

score 3 · Accepted Answer · answered Apr 29 '11 at 22:18

If you want to build-up an existing instance through property and method injection, you can use the following:

var model = new CustomerViewModel(customer);
model = container.BuildUp(model);

In general I would not recommend using this feature of Unity. Sometimes you need it, but it's usually a warning sign that could be fixed by adjusting the design a bit to work more naturally with IoC as a pattern (not a framework). With more details on how you are using it, the SO community can probably offer some other options...

Thanks Michael, although I'm trying to avoid using 'new' in my controller and want my factory to supply new instances using generic methods that use Unity. — sturdytree, May 02 '11 at 08:22

score 1 · Answer 2 · answered Apr 29 '11 at 18:47

Since the dependency injection container is designed to provide finished objects, you'll need to use a factory pattern (which is quite common in these cases) to achieve your desired configuration:

public interface ICustomerViewModelFactory {
   public ICustomerViewModel GetModelFor(ICustomer customer);
}

public class CustomerViewModelFactory : ICustomerViewModelFactory {
   public ICustomerViewModel GetModelFor(ICustomer customer) {
      return new CustomerViewModel(customer);
   }
}

// elsewhere...
container.RegisterInstance<ICustomerViewModelFactory>(new CustomerViewModelFactory());

// and finally...
ICustomerViewModelFactory factory = container.Resolve<ICustomerViewModelFactory>();
ICustomerViewModel customerViewModel = factory.GetModelFor(existingCustomer);

Thanks Jollymorphic, but I was hoping to keep the factory as generic as possible for as long as possible. — sturdytree, Apr 29 '11 at 20:09

score 0 · Answer 3 · edited May 23 '17 at 12:15

0

Check the 'Can I pass constructor parameters to Unity's Resolve() method?' question (also on Stack Overflow).

edited May 23 '17 at 12:15

Community

1
1

answered Apr 29 '11 at 21:35

Damian Schenkelman

3,505
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That's useful, thanks Damian. However, using parameter overrides seems to require using the name of the parameter as a string (brittle design) and using InjectionConstructor requires registering the instance (existingCustomer in my example) in the container. That's impractical when converting many existing domain objects to viewmodels - the conclusion seems to be Unity does not yet allow this. – sturdytree May 02 '11 at 08:26

Using Microsoft Unity IOC, how can you pass it an existing object to inject?

3 Answers3