Don't emit duplicate consecutive MviViewStates.

vlazzle · vlazzle · commit c3d98c3edc8d · 2018-02-16T14:34:20.000-08:00
See #31
diff --git a/app/src/main/java/com/example/android/architecture/blueprints/todoapp/addedittask/AddEditTaskViewModel.kt b/app/src/main/java/com/example/android/architecture/blueprints/todoapp/addedittask/AddEditTaskViewModel.kt
@@ -88,6 +88,10 @@ class AddEditTaskViewModel(
         // the previous cached one and the latest Result emitted from the action processor.
         // The Scan operator is used here for the caching.
         .scan(AddEditTaskViewState.idle(), reducer)
+        // When a reducer just emits previousState, there's no reason to call render. In fact,
+        // redrawing the UI in cases like this can cause jank (e.g. messing up snackbar animations
+        // by showing the same snackbar twice in rapid succession).
+        .distinctUntilChanged()
         // Emit the last one event of the stream on subscription
         // Useful when a View rebinds to the ViewModel after rotation.
         .replay(1)
diff --git a/app/src/main/java/com/example/android/architecture/blueprints/todoapp/statistics/StatisticsViewModel.kt b/app/src/main/java/com/example/android/architecture/blueprints/todoapp/statistics/StatisticsViewModel.kt
@@ -84,6 +84,10 @@ class StatisticsViewModel(
         // the previous cached one and the latest Result emitted from the action processor.
         // The Scan operator is used here for the caching.
         .scan(StatisticsViewState.idle(), reducer)
+        // When a reducer just emits previousState, there's no reason to call render. In fact,
+        // redrawing the UI in cases like this can cause jank (e.g. messing up snackbar animations
+        // by showing the same snackbar twice in rapid succession).
+        .distinctUntilChanged()
         // Emit the last one event of the stream on subscription.
         // Useful when a View rebinds to the ViewModel after rotation.
         .replay(1)
diff --git a/app/src/main/java/com/example/android/architecture/blueprints/todoapp/taskdetail/TaskDetailViewModel.kt b/app/src/main/java/com/example/android/architecture/blueprints/todoapp/taskdetail/TaskDetailViewModel.kt
@@ -87,6 +87,10 @@ class TaskDetailViewModel(
         // the previous cached one and the latest Result emitted from the action processor.
         // The Scan operator is used here for the caching.
         .scan(TaskDetailViewState.idle(), reducer)
+        // When a reducer just emits previousState, there's no reason to call render. In fact,
+        // redrawing the UI in cases like this can cause jank (e.g. messing up snackbar animations
+        // by showing the same snackbar twice in rapid succession).
+        .distinctUntilChanged()
         // Emit the last one event of the stream on subscription
         // Useful when a View rebinds to the ViewModel after rotation.
         .replay(1)
diff --git a/app/src/main/java/com/example/android/architecture/blueprints/todoapp/tasks/TasksViewModel.kt b/app/src/main/java/com/example/android/architecture/blueprints/todoapp/tasks/TasksViewModel.kt
@@ -92,6 +92,10 @@ class TasksViewModel(
         // the previous cached one and the latest Result emitted from the action processor.
         // The Scan operator is used here for the caching.
         .scan(TasksViewState.idle(), reducer)
+        // When a reducer just emits previousState, there's no reason to call render. In fact,
+        // redrawing the UI in cases like this can cause jank (e.g. messing up snackbar animations
+        // by showing the same snackbar twice in rapid succession).
+        .distinctUntilChanged()
         // Emit the last one event of the stream on subscription
         // Useful when a View rebinds to the ViewModel after rotation.
         .replay(1)
