MEF getting exports with a string

Question

Is it possible to get exports by only have a string? The parts are in the container but I only have a string to resolve the correct part. MEF seems to want types to resolve, and things like Type.GetType() require a hard reference. Can't use a generic interface, need very specific parts.

The string can be changed to match what ever is needed. (I think)

container.GetExports("ClassLibrary1.Class1")

I haven't played with the metadata stuff but can you resolve based on a metadata string?

Thanks

Answer 1

If you're trying to get parts without a reference to the type, what are you hoping to accomplish with the part once you have it? Also note that you can reference a type without an object using typeof or by using generic methods.

This is why MEF is usually wired up using public interfaces, rather than concrete and/or nonpublic types.

What you're looking for is the default Contract Name for a given type, however any helper methods for looking up that default name will require the Type object and fall under the same explanation as above.

EDIT: The above applies if you're trying to find the contract name for a given class. For differentiating exports of the same type, see below

When exporting, you can specify both a contract name and export type, such as

[Export("Contract", typeof(IInterface))]
public class Part : IInterface { /*...*/ }

This can allow you to differentiate between multiple parts. If you want the part imported as part of an ImportMany directive, you must also export it without a contract name, such as

[Export("Contract", typeof(IInterface))]
[Export(typeof(IInterface))]
public class Part : IInterface { /*...*/ }

Since attributes are allowed to take const values, it may also be useful to specify the individual contract names in a collection of names, IE

public static class ContractNames
{
    public const string Contract = "Contract";
}

[Export(ContractNames.Contract, typeof(IInterface))]
[Export(typeof(IInterface))]
public class Part : IInterface { /*...*/ }

...
    container.GetExportedValue<IInterface>(ContractNames.Contract);

Note the above uses GetExportedValue instead of GetExports since the former will directly compose and return values, instead of export metadata