Include minor changes from extensions PR

app/src/main/java/eu/kanade/tachiyomi/ui/base/presenter/BasePresenter.kt

@@ -1,6 +1,7 @@
 package eu.kanade.tachiyomi.ui.base.presenter
 
 import nucleus.presenter.RxPresenter
+import nucleus.presenter.delivery.Delivery
 import rx.Observable
 
 open class BasePresenter<V> : RxPresenter<V>() {
@@ -35,4 +36,29 @@ open class BasePresenter<V> : RxPresenter<V>() {
     fun <T> Observable<T>.subscribeReplay(onNext: (V, T) -> Unit, onError: ((V, Throwable) -> Unit)? = null)
             = compose(deliverReplay<T>()).subscribe(split(onNext, onError)).apply { add(this) }
 
+    /**
+     * Subscribes an observable with [DeliverWithView] and adds it to the presenter's lifecycle
+     * subscription list.
+     *
+     * @param onNext function to execute when the observable emits an item.
+     * @param onError function to execute when the observable throws an error.
+     */
+    fun <T> Observable<T>.subscribeWithView(onNext: (V, T) -> Unit, onError: ((V, Throwable) -> Unit)? = null)
+            = compose(DeliverWithView<V, T>(view())).subscribe(split(onNext, onError)).apply { add(this) }
+
+    /**
+     * A deliverable that only emits to the view if attached, otherwise the event is ignored.
+     */
+    class DeliverWithView<View, T>(private val view: Observable<View>) : Observable.Transformer<T, Delivery<View, T>> {
+
+        override fun call(observable: Observable<T>): Observable<Delivery<View, T>> {
+            return observable
+                    .materialize()
+                    .filter { notification -> !notification.isOnCompleted }
+                    .flatMap { notification ->
+                        view.take(1).filter { it != null }.map { Delivery(it, notification) }
+                    }
+        }
+    }
+
 }