injecting generics with roboguice

问题

I'm trying to inject instances with generics and i'm getting the following error:

HasOne<ModelClass> cannot be used as a key; It is not fully specified.

I've read elsewhere that safest way to do this is to explicitly name the class to be used in the generic when using the injector to get an instance but i'd like to be a little cleaner. I'm trying to create Relationship objects between Models.

Here is my simplified Model class

public class Model {

    @Inject
    Injector injector;

    public <ModelClass extends Model> HasOne<ModelClass> hasOne(Class<ModelClass> clazz) {

        HasOne<ModelClass> hasOne = injector.getInstance(Key.get(new TypeLiteral<HasOne<ModelClass>>() {
        }));

        hasOne.init(clazz);

        return hasOne;
    }
}

My HasOne relationship

public class HasOne<T extends Model> {

    Class clazz;

    public void init(Class<T> clazz){
        this.clazz = clazz;
    }

    @Inject
    Injector injector;

    public T get(){

        return (T) injector.getInstance(clazz);
    }
}

Test Model #1

public class TestModel extends Model {

    public HasOne<ExampleModel> exampleModel(){

        return hasOne(ExampleModel.class);
    }
}

Test Model #2

public class ExampleModel extends Model {
}

I get the error when doing this

    TestModel testModel = RoboGuice.getInjector(context).getInstance(TestModel.class);

    HasOne<ExampleModel> relationship = testModel.exampleModel();

I'm trying to hide away the ugly relationship creation and keep it in the Model class

回答1:

You cannot use new TypeLiteral<T>() { } if T is a type parameter, it has to be a fully-specified type. Luckily, since you have an instance of Class<ModelClass>, you can do this:

(Key<HasOne<ModelClass>>) Key.get(TypeLiteral.get(Types.newParameterizedType(HasOne.class, clazz)))

You'll get a warning on the cast but it is safe to suppress it.

来源：https://stackoverflow.com/questions/17617005/injecting-generics-with-roboguice