Question

I’m writing a game for Android with Scala. Now I’m trying to get the Dick Wall’s new Dependency Injection framework SubCut to work on Android.

Basically I have a class that extends android.app.Activity, which is the game’s only activity and started automatically by Android when the application starts. Now I would need to let this Activity instance be injected by SubCut.

Normally you do it like:

implicit val bindingModule = ProjectConfiguration
val topInstance = new DoStuffOnTheWeb("stuff", new Date())

or

val topInstance = new DoStuffOnTheWeb("stuff", new Date())(ProjectConfiguration)

but the problem is that the Activity is instantiated by android, not from my code. I tried using something like this:

class MyGame()(val bindingModule:BindingModule = MyGameConfigurationModule) extends Activity with Injectable {

but apparently android doesn’t know how to instantiate this as I now get:

ERROR/AndroidRuntime(322): FATAL EXCEPTION: main
    java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.mycompany.android.mygame.....

I was thinking whether it would be possible to “bootstrap” the SubCut somehow in the activity’s onCreate() method, as the RoboGuice does with Guice DI framework (it creates an injector instance in that method and passes it this as parameter.

Other option I thought about was if I could skip the automatic starting of the Activity and manually start it from android.app.Application with the implicit val required by the Subcut. But somehow this feels like asking for trouble (and yeah, I’m very new to android development).

Any ideas?

Answer 1

Well, off the top of my head, perhaps the best option here would be to go with a mixin based solution for providing the binding module instead. You can do this pretty easily:

trait ProjectBindings {
  implicit val bindingModule: BindingModule = MyGameConfigurationModule
}

and then mix this in along with the injectable trait:

class MyGame extends Injectable with ProjectBindings {
  // ...
}

This is the technique I use with frameworks like wicket where you can’t hook into the creation of new instances without a lot of hassle, so I believe it should work with the Android activity use case as well. I would be interested to know if it does. Of course, the problem with this approach is that it is not very flexible with regards to reconfiguring, which is why I prefer the implicit val in the curried constructor parameter approach, but it does work just fine.

Hope that helps.

Dick