Generic parameter in method

Question

Hi

I have a class:

Class ClassA
{
   public void doSomething()
   {
      // This line doesn't work and needs fix.
      IPresenterBase<T> presenter = container.Resolve<IPresenterBase<T>>();
   }
}

The method signature for Resolve:

T Resolve<T>();

How should i change the implementation of class "ClassA" or method "doSomething" so that the line gets fixed meaning i could pass a generic type?

Answer 1

public void doSomething<T>()
   {
      // This line doesn't work and needs fix.
      IPresenterBase<T> presenter = container.Resolve<IPresenterBase<T>>();
   }

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Vitaliy Liptchinsky http://dotnetframeworkplanet.blogspot.com/

Answer 2

You need to give a context for "T".  What type is T here?

Either create a generic type parameter for the method, or create one for the class.

Class ClassA<T>
{
   public void doSomething()
   {
      // This line doesn't work and needs fix.
      IPresenterBase<T> presenter = container.Resolve<IPresenterBase<T>>();
   }
}

or

Class ClassA
{
   public void doSomething<T>()
   {
      // This line doesn't work and needs fix.
      IPresenterBase<T> presenter = container.Resolve<IPresenterBase<T>>();
   }
}

or decalare the type parameter directly:

Class ClassA
{
   public void doSomething()
   {
      // This line doesn't work and needs fix.
      IPresenterBase<ISomeInterface> presenter = container.Resolve<IPresenterBase<ISomeInterface>();
   }
}

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Coding Light - Illuminated Ideas and Algorithms in Software
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Answer 3

Weird for i get an error when i tried first and second proposal:

The type 'T' cannot be used as type parameter 'T' in the generic type or method 'PLVS.Infrastructure.Presenters.IPresenterBase<T>'. There is no boxing conversion or type parameter conversion from 'T' to 'PLVS.Infrastructure.Views.IViewBase'.

What i didn't mention in my first posting is the definition of IPresenterBase:

    public interface IPresenterBase<T> where T : IViewBase
    {
        T View { get; set; }
    }

Answer 4

The constraints have to be honored everywhere... hence:

Class ClassA<T> where T : IViewBase
{
   public void doSomething()
   {
      // This line doesn't work and needs fix.
      IPresenterBase<T> presenter = container.Resolve<IPresenterBase<T>>();
   }
}

or

Class ClassA
{
   public void doSomething<T>() : where T : IViewBase
   {
      // This line doesn't work and needs fix.
      IPresenterBase<T> presenter = container.Resolve<IPresenterBase<T>>();
   }
}

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Coding Light - Illuminated Ideas and Algorithms in Software
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Answer 5

Thanks.

How can i change the interface property to a generic type? e.g. 

    public interface IPresenterBase<T> where T : IViewBase
    {
        T View { get; set; }
    }

I don't want the interface to have a generic parameter only the property.

Something like (needs fixing):

    public interface IPresenterBase
    {
        T View  where T : IViewBase { get; set; }
    }

Answer 6

Sorry, you can't do that.  You can't declare a generic property without a generic class or interface surrounding it.  You can declare a generic method without the generic interface surrounding it, which is what I showed above, but you can't ever have a simply generic property without some sort of overarching context, such as a generic parameter in the class or interface declaration. 

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