What is the proper way to have a singleton while u...

# dagger

[Sinan Gunes]

What is the proper way to have a singleton while using assisted injection. I mean same @Assisted parameter should return same object.

[wasyl]

You pass assisted parameters yourself, so you control their lifecycle

[Sinan Gunes]

using AssistedFactory or hand made?

[wasyl]

I’m not sure I understand what you mean, can you give an example of what you want to achieve?

[Sinan Gunes]

basically I am trying to create a Retrofit WebService, but Base Url is provided runtime.

[Sinan Gunes]

simply this worked, however it returns a new WebService everytime:

class ChatRepositoryImpl @AssistedInject constructor(@Assisted("baseUrl") baseUrl: String)
    : ChatRepository by buildRetrofit(baseUrl).create(ChatRepository::class.java) {
}


@AssistedFactory
interface ChatRepoFactory {
    @Singleton
    fun create(@Assisted("baseUrl") baseUrl: String): ChatRepositoryImpl
}

[wasyl]

If I understand correctly, your @Singleton is in wrong place — it should be placed at class ChatRepositoryImpl, just like you would with a regular @Inject

[Sinan Gunes]

you can ignore this @Singleton there, because it is not working. Also Dagger does not allow me to put above ChatRepositoryImpl. :

Assisted Injection cannot be scoped

[wasyl]

Ah right. In that case you need to scope the class in which you’re creating the repository.

[wasyl]

It’s not possible to return the same instance from a factory because what should Dagger do if you try to do something like this:

val instance1 = factory.create(baseUrl = "foo")
val instance2 = factory.create(baseUrl = "bar")

?

[Sinan Gunes]

I would expect to return different instances.

[Sinan Gunes]

my case seems an edge one. I will cache instances somewhere if there is no other way.

[wasyl]

I would expect to return different instances.

If you want to return the same instances for the same `baseUrl`s then you just need to do that manually, Dagger won’t do that for you. So you’d need a @Singleton-scoped class which will internally hold ChatRepoFactory and cache the returned instances for the same urls

[Sinan Gunes]

sounds good. better than I originally thought. thanks @wasyl 👍🏻