Dagger 2 injecting multiple instances of same object type

Question

Background

I am converting my app to MVP architecture and found Dagger 2 to be useful to inject dependencies when needed. My app needs to communicat

Answer 1

You are already halfway through the solution. To complete the solution try to do the following:

@Provides
@Named("myApiRestAdapter")
RestAdapter provideMyRestAdapter(@Named("myApiGson") Gson gson, OkHttpClient okHttpClient) {
   return new RestAdapter.Builder()
            .setEndpoint(MY_API_URL)
            .setConverter(new GsonConverter(gson))
            .setClient(new OkClient(okHttpClient))
            .build();
}

@Provides
@Named("thirdPartyApiRestAdapter")
RestAdapter provideThirdPartyRestAdapter(@Named("thirdPartyApiGson") Gson gson, OkHttpClient okHttpClient) {
   return new RestAdapter.Builder()
            .setEndpoint(THIRD_PARTY_API_URL)
            .setConverter(new GsonConverter(gson))
            .setClient(new OkClient(okHttpClient))
            .build();
}

To make sure that only two instances of your RestAdapters are created during the lifetime of the application, annotate both the methods providing RestAdapter with @Singleton like you have done with your other methods. As for your other question whether Dagger 2 will create new instance of RestAdapter every time it has to inject it, I think it does this exactly, but I'm not sure on this.

Hope this helps!

Answer 2

I saw this thread after posting my answer to a similar question. I wanted to provide a link because I think the same approach could be useful depending on your situation. It may be overkill for this exact question but I wanted to share in case it helps someone else.

https://stackoverflow.com/a/52348744/5046784

In short you can create unique interfaces / classes for each named object(e.g. MyApiGson and ThirdPartyApiGson) and then create @Provides for those rather than the generic Gson class. This way you can inject the instances by class/interface rather than a magic string name that you need to lookup or remember. Its a little more work but it helps when you have a bunch of independent modules that provide difference instances of the same Class.