@Inject an OSGi Service

[Frizz]

I have a OSGi service that I'd like to inject in one of my bundles.
When I use @Inject it's always Null - and I don't understand why. Is it not
possible to use @Inject in a BundleActivator?

When I manually access the Service Registry (-> see start() method) it
works fine.

public class ClientActivator implements BundleActivator {

    @Inject
    IMyService service;

    @Override
    public void start(BundleContext context) throws Exception {
        System.out.println(service); // -> Null

        ServiceReference reference =
context.getServiceReference(IMyService.class.getName());
        IMyService service = (IMyService) context.getService(reference);
        System.out.println(service); // -> not Null
    }
...
}