Dagger with Android: How do I inject the current context?

Question

Back when I used RoboGuice, I was able to constructor inject Context into of my classes and RoboGuice would pick the appropriate Context (injects in an Activity would have the Activity context, injects in Application would have the current application context, injects in a Fragment would have the fragment's activity's context, etc...).

Is there a similar method for achieving this with Dagger?

public class Thing {
    @Inject
    public class Thing(Context context){
       // if i'm injected in an Activity, I should be the current activity's context
       // if i'm injected in an Fragment, I should be the fragment's activity context
       // if i'm injected in a Service, I should be the service's context
       // etc...
    }
}

Answer 1

Dagger doesn't know about Android. Or anything, really. If you want to inject something, you have to tell Dagger about it.

You can see an example of how to inject a Context in the examples. In this case, a qualifier is used to differentiate the application one from an activity one.

/**
 * Allow the application context to be injected but require that it be annotated with
 * {@link ForApplication @Annotation} to explicitly differentiate it from an activity context.
 */
@Provides @Singleton @ForApplication Context provideApplicationContext() {
  return application;
}

Edit

No, you cannot inject an unqualified type and have the instance of that type change based on the context in which you are performing injection. Dagger requires that the source of a type is known at compile-time and since object graphs are immutable that source cannot be changed.

The only way to do this is to use a factory which allows you to specify the context with which the object will be created.

public final class ThingFactory {
  private final Foo foo;
  private final Bar bar;

  @Inject public ThingFactory(Foo foo, Bar bar) {
    this.foo = foo;
    this.bar = bar;
  }

  public Thing get(Context context) {
    return new Thing(context, foo, bar);
  }
}