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Ticket T309140
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ArgumentNullException in MS Unity Container & MVVM POCO

created 9 years ago

Hello DX Team

I'm trying to use a MS Unity IoC container with the MVVM framework.
I'm creating POCO view model with constructor injection but I keep getting ArgumentNullException (parameter name "source").
Reproduce sln is attached.

My example

C#
var container = new UnityContainer();  

// It's ok  
var pocoVMWithoutParameterInCtorInstance = container  
    .Resolve(ViewModelSource.GetPOCOType(typeof (VMWithoutParameterInCtor)));  

// It's ok  
var withoutViewModelSource = container.Resolve(typeof(VMWithParameterInCtor));  

// It's throw  
var pocoViewModelInstance = container  
    .Resolve(ViewModelSource.GetPOCOType(typeof (VMWithParameterInCtor)));  
C#
[POCOViewModel]  
public class VMWithoutParameterInCtor { }  

[POCOViewModel]  
public class VMWithParameterInCtor  
{  
    public VMWithParameterInCtor(SomeClass someClass)  
    {  
    }  
}  

public class SomeClass { }
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Answers

created 9 years ago (modified 9 years ago)

Hello Anton,

You have to register the types with ViewModelSource.GetPOCOType method (to emit a ViewModel from the POCO) and then to resolve the ViewModels by POCO types:

C#
var container = new UnityContainer();  

container.RegisterType(ViewModelSource.GetPOCOType(typeof(VMWithoutParameterInCtor)));  
container.RegisterType(ViewModelSource.GetPOCOType(typeof(VMWithParameterInCtor)));  

var withoutParameter = container  
    .Resolve(typeof(VMWithoutParameterInCtor));  

var withParameter = container  
    .Resolve(typeof(VMWithParameterInCtor));

Best regards,
Mikhail

    Show previous comments (2)
    M M
    Mikhail Shubin [DevExpress MVP] 9 years ago

      Hello Anton,
      Yes, I use SimpleInjector, now Unity…
      It seems you have to use special Register method:
         var container = new UnityContainer();
         container.RegisterType(typeof(VMWithoutParameterInCtor), ViewModelSource.GetPOCOType(typeof(VMWithoutParameterInCtor)));
         container.RegisterType(typeof(VMWithParameterInCtor),
      ViewModelSource.GetPOCOType(typeof(VMWithParameterInCtor)), new InjectionConstructor(new SomeClass()));
         var withoutParameter = container.Resolve<VMWithoutParameterInCtor>();
         var withParameter = container.Resolve<VMWithParameterInCtor>();
      Now it works.
      In SimpleInjector case it looks simpler:
           //  SimpleInjection Container: https://simpleinjector.readthedocs.org/en/latest/index.html
           var simpleContainer = new Container();
           simpleContainer.Register(typeof(VMWithoutParameterInCtor), ViewModelSource.GetPOCOType(typeof(VMWithoutParameterInCtor)));
           simpleContainer.Register(typeof(VMWithParameterInCtor), ViewModelSource.GetPOCOType(typeof(VMWithParameterInCtor)));
           //  Optional registration for injecton
           //simpleContainer.RegisterSingleton<SomeClass>();
           //  Optional verification
           //simpleContainer.Verify();
           var instance1 = simpleContainer.GetInstance<VMWithoutParameterInCtor>();
           var instance2 = simpleContainer.GetInstance<VMWithParameterInCtor>();
      The sample project is attached.
      Thanks,
      Mikhail

      AO AO
      Anton Ok. 9 years ago

        Hello, Mikhail.
        Thanks again for your help.
        About registration
        Yours variant of registration must be working.
        But this mean that I need register all my view models with all it's constructor parameters!
        If I use Generic view models (MyViewModel<T>) I need register all variations of it (ex: MyViewModel<int>, MyViewModel<string>, …).
        And I need support registrations during app life. It's not cool )
        About Unity
        My first question was exactly about MS Unity - how to use MS Unity with DX MVVM Framework.
        ViewModel without poco emit logic works fine (without any extra registrations)
          var withParameter = container.Resolve(typeof(VMWithParameterInCtor));
        after emit - simple way is not working )
        About SimpleInjector
        It also not solve problem with registration requirement. It's make the registration simpler.
        And I'm not ready to change my DI library )

        DevExpress Support Team 9 years ago

          Hi Anton,
          Thank you for your patience. We have researched this issue and it appears that we have found a way to resolve it on our side. If everything goes according to plan, the code you initially posted will work without additional modifications. I have created a separate report about the exception - ArgumentNullException exception occurs when calling UnityContainer.Resolve for a type created using ViewModelSource.GetPOCOType. We will update it once we have any news.

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