Define Generic Type T dynamically at runtime

Question

1. I have a function DoSomeService with object response as parameter. response are different classes the internal code decides which one to use dynamically at runtime.

2. I have a generic Fluent Validator< T> that takes in the type of a response class, then validates it.

Now, I can do type checking one by one:

public override void DoSomeService(object response) {
    object validator = null;
    if (response.GetType()==typeof(TypeA_Response)) validator= new Validator<TypeA_Response>();
    if (response.GetType()==typeof(TypeB_Response)) validator= new Validator<TypeB_Response>();
    if (response.GetType()==typeof(TypeC_Response)) validator= new Validator<TypeC_Response>();
    //......
    if (response.GetType()==typeof(TypeX_Response)) validator= new Validator<TypeX_Response>();
        if (validator.IsValid) {
        //do more stuff ...
    }
}

But that is not nice, especially when I have many responses. I want something short and generic.

//response could be TypeA_Response, TypeB_Response, TypeX_Response
public override void DoSomeService(object response) {
    var validator = new Validator<T>();
    if (validator.IsValid) {
        //do more stuff ...
    }
}

Of course, this won't work because I need to define T for Fluent Validator. How do I detect what type is "object response" and fill it into T dynamically at runtime?

Or how do I avoid doing this all together and have a better structure for my validator< T>?

Note, I can't change the base Service class and DoSomeService function signature, it is an override function from 3rd party package.

Can you use an interface, IValidator, and then make each implementation of IValidator have a Validate() method that encapsulates its own validation for that type? This would reduce the need for the unknown generic, I would think. — Dmitriy Khaykin, Mar 09 '13 at 01:22

score 2 · Accepted Answer · answered Mar 09 '13 at 00:50

If you truly want this to be dynamic the best way is to use reflection

void DoSomething(object response)
{
    var type = typeof(Validator<>);
    var boundType = type.MakeGenericType(response.GetType());
    var validator = Activator.CreateInstance(boundType);
}

Even with this solution though you won't be able to use Validator<T> in this context because you still don't know what T is. T must be defined statically to be used in this manner. You will need to break up Validator<T> to a generic and non-generic base type and use the non-generic type within the DoSomething method

Validator valdiator = Activator.CreateInstance(boundType);

score 1 · Answer 2 · answered Mar 09 '13 at 00:48

1

That's not really what generics is for. Rather, you would have either a base class with virtual methods that do the validation or have a requirement that the concrete types implement a particular interface that has the validation methods on it.

answered Mar 09 '13 at 00:48

500 - Internal Server Error

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I have simplified my question, the real code is actually sitting in an ValidationAspect interceptor in a Windsor method selector. Same question applies, no matter which method comes through the interceptor, I want to generalise it. I don't want to run if statements as I show above. – Tom Mar 09 '13 at 00:54

Define Generic Type T dynamically at runtime

2 Answers2