如何在C＃中通过反射使用泛型创建对象

Question

I need to find all the instances of objects which implement interface IFOO. Then create the object and find some values of some properties of the object.

public interface IFoo
{

}
public class FooModel
{
    public string Code { get; set; }
}


public class Foo<FooModel> : IFoo
{

}

public class Create{

    public void CreateInstances()
    {
        var itype = typeof(IFoo);
        var types = (from domainAssembly in AppDomain.CurrentDomain.GetAssemblies()
                     from assemblyType in domainAssembly.GetTypes()
                     where itype.IsAssignableFrom(assemblyType)
                     select assemblyType).Where(m => m != itype);
        foreach (var type in types)
        {
            var genericArgs = type.GetGenericArguments();
            var makeme = type.MakeGenericType(genericArgs);
            var newObject = Activator.CreateInstance(makeme);

        }
    }
}

However when the newObject is created I get the following error:

Cannot create an instance of Foo`1[FooModel] because Type.ContainsGenericParameters is true

Answer 1

This is not what you may expect:

public class Foo<FooModel> : IFoo
{
}

FooModel is not your FooModel class here but a simple type parameter. You might want to define it like this:

public class Foo<T> : IFoo where T: FooModel
{
}

However, this will not solve you problem just makes it better understandable.

Your code just finds the generic type and tries to instantiate it like this:

new Foo<>();

But this will not work of course because your genericArgs contains a generic type definition ( T ) instead of a constructed type ( FooModel ). Do it like this to make it work:

var makeme = type.MakeGenericType(new Type[] { typeof(FooModel) });