获取通用接口的实现类型

Question

I have an generic interface and I would like to have a list of the implemented data types. With the following code I don't get any type returned. (t in types)

var type = typeof (IDataTypeConverter<>);
var types = AppDomain.CurrentDomain.GetAssemblies()
                     .SelectMany(x => x.GetTypes())
                     .Where(x => type.IsAssignableFrom(x) && !x.IsInterface);

foreach (var t in types)
{
    var instance = (IDataTypeConverter)Activator.CreateInstance(t); 
    PropertiesConverter.Add(t, instance);
}

This is an example of an implementation of the interface:

public class DecimalConverter : IDataTypeConverter, IDataTypeConverter<decimal>
    {
     ...
    }

Interface it selves:

public interface IDataTypeConverter
{
    object Convert(object value);
}

public interface IDataTypeConverter<TDataType>
{

}

What am I doing wrong here, why don't I get decimal as a type in my list?

Answer 1

You're almost there. You're checking to see if your classes are assignable to the open generic type IDataTypeConverter<> which they are not. They are only assignable to a closed generic type like IDataTypeConverter<decimal> (or other data types for TDataType )

var type = typeof (IDataTypeConverter<>);
var types = AppDomain.CurrentDomain.GetAssemblies()
    .SelectMany(x => x.GetTypes())
    .Where(x => !x.IsInterface) //ignore interface definitions
    .Where(x => x.GetInterfaces() //for each interface implemented
        .Where(i => i.IsGenericType) //if they're a generic interface
        .Any(i => i.GetGenericTypeDefinition() == type)); //check its open-generic

I think there might be a simpler way to check, but this will do the job. It grabs all interfaces for a type, and for each one that's a generic interface, it checks if it's underlying open generic definition is IDataTypeConverter<> .

EDIT: Another way to demonstrate what I mean, your existing code would work if for type you assigned typeof(IDataTypeConverter<decimal>) instead. That works because your types would be assignable to a IDataTypeConverter<decimal> but they're not assignable to IDataTypeConverter<> because such an operation has no meaning in C#.

Answer 2

Your type variable contains generic type definition, IDataTypeConverter is not its descendant. So IDataTypeConverter is not assignable from IDataTypeConverter<>.

Console.WriteLine(typeof(IDataTypeConverter<>).IsGenericTypeDefinition);
Console.WriteLine(typeof(IDataTypeConverter<decimal>).IsGenericTypeDefinition);

To check that some generic type is of the same generic type definition you can use predicate:

x => .GetInterfaces()
     .Any(item => item.IsGenericType && item.GetGenericTypeDefinition() == type)