Generates Bitmap Observables with Picasso instance

PicassoImageObservable.kt

class PicassoImageObservable(
    private val picasso: Picasso
) : Func1<String, Observable<Bitmap>> {

  override fun call(url: String): Observable<Bitmap> {
    return Observable.fromAsync({ emitter ->
      val target = object : Target {
        override fun onPrepareLoad(placeHolderDrawable: Drawable?) {
          //do nothing
        }

        override fun onBitmapFailed(errorDrawable: Drawable?) {
          // our use case does not have an error drawable
          emitter.onCompleted()
        }

        override fun onBitmapLoaded(bitmap: Bitmap, from: LoadedFrom) {
          emitter.onNext(bitmap)
          emitter.onCompleted()
        }
      }
      picasso.load(url).into(target)

      // cancel the request if the end user unsubscribes
      emitter.setCancellation { picasso.cancelRequest(target) }
    }, NONE)
  }
}