Add a TransformedLiveData that do transformations on the background

app/src/main/java/chat/rocket/android/chatrooms/viewmodel/ChatRoomsViewModel.kt

@@ -9,10 +9,11 @@ import chat.rocket.android.chatrooms.adapter.RoomMapper
 import chat.rocket.android.chatrooms.domain.FetchChatRoomsInteractor
 import chat.rocket.android.chatrooms.infrastructure.ChatRoomsRepository
 import chat.rocket.android.server.infraestructure.ConnectionManager
+import chat.rocket.android.util.livedata.TransformedLiveData
 import chat.rocket.core.internal.realtime.socket.model.State
 import kotlinx.coroutines.experimental.launch
+import kotlinx.coroutines.experimental.newSingleThreadContext
 import me.henrytao.livedataktx.distinct
-import me.henrytao.livedataktx.map
 import me.henrytao.livedataktx.nonNull
 import timber.log.Timber
 
@@ -23,33 +24,43 @@ class ChatRoomsViewModel(
     private val mapper: RoomMapper
 ) : ViewModel() {
     private val ordering: MutableLiveData<ChatRoomsRepository.Order> = MutableLiveData()
+    private val runContext = newSingleThreadContext("chat-rooms-view-model")
 
     init {
         ordering.value = ChatRoomsRepository.Order.ACTIVITY
     }
 
     fun getChatRooms(): LiveData<List<ItemHolder<*>>> {
-        // TODO - add a loading status...
-        launch { interactor.refreshChatRooms() }
-
         return Transformations.switchMap(ordering) { order ->
             Timber.d("Querying rooms for order: $order")
             val grouped = order == ChatRoomsRepository.Order.GROUPED_ACTIVITY
                     || order == ChatRoomsRepository.Order.GROUPED_NAME
-            repository.getChatRooms(order).nonNull()
-                    .distinct()
-                    .map { rooms ->
-                        Timber.d("Mapping rooms to items: $rooms")
-                        mapper.map(rooms, grouped)
-                    }
+            val roomData = repository.getChatRooms(order).nonNull().distinct()
+            TransformedLiveData(runContext, roomData) { rooms ->
+                rooms?.let {
+                    mapper.map(rooms, grouped)
+                }
+            }.nonNull()
         }
     }
 
     fun getStatus(): MutableLiveData<State> {
-        return connectionManager.statusLiveData.nonNull().distinct()
+        return Transformations.map(connectionManager.statusLiveData.nonNull().distinct()) { state ->
+            if (state is State.Connected) {
+                // TODO - add a loading status...
+                fetchRooms()
+            }
+            state
+        }.nonNull()
+    }
+
+    private fun fetchRooms() {
+        launch {
+            interactor.refreshChatRooms()
+        }
     }
 
     fun setOrdering(order: ChatRoomsRepository.Order) {
         ordering.value = order
     }
-}
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+}

app/src/main/java/chat/rocket/android/util/livedata/TransformedLiveData.kt

+package chat.rocket.android.util.livedata
+
+import androidx.lifecycle.LiveData
+import androidx.lifecycle.Observer
+import kotlinx.coroutines.experimental.CommonPool
+import kotlinx.coroutines.experimental.Job
+import kotlinx.coroutines.experimental.android.UI
+import kotlinx.coroutines.experimental.launch
+import kotlinx.coroutines.experimental.withContext
+import timber.log.Timber
+import kotlin.coroutines.experimental.CoroutineContext
+
+
+class TransformedLiveData<Source, Output>(
+    private val runContext: CoroutineContext = CommonPool,
+    private val source: LiveData<Source>,
+    private val transformation: (Source?) -> Output?)
+    : LiveData<Output>() {
+    private var job: Job? = null
+
+    private val observer = Observer<Source> { source ->
+        job?.cancel()
+        job = launch(runContext) {
+            transformation(source)?.let { transformed ->
+                withContext(UI) {
+                    value = transformed
+                }
+            }
+        }
+    }
+
+    override fun onActive() {
+        Timber.d("Attaching observer")
+        source.observeForever(observer)
+    }
+
+    override fun onInactive() {
+        Timber.d("Detaching observer")
+        job?.cancel()
+        source.removeObserver(observer)
+    }
+}
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