Update docs and versions for publishing for ScrollOffsetListener (#473)

* Update readme for scroll offset

* Update version for releasing scroll offset listening

Author: tarobins

packages/scrollable_positioned_list/CHANGELOG.md

@@ -1,3 +1,6 @@
+# 0.3.7
+* Add ScrollOffsetListener to allow listening to changes in scroll offset.
+
 # 0.3.6
 * Fix cache extents for horizontal lists
 * scrollTo future doesn't complete until scrolling is done.

packages/scrollable_positioned_list/README.md

@@ -16,12 +16,14 @@ A `ScrollablePositionedList` can be created with:
 ```dart
 final ItemScrollController itemScrollController = ItemScrollController();
 final ItemPositionsListener itemPositionsListener = ItemPositionsListener.create();
+final ScrollOffsetListener scrollOffsetListener = ScrollOffsetListener.create()
 
 ScrollablePositionedList.builder(
   itemCount: 500,
   itemBuilder: (context, index) => Text('Item $index'),
   itemScrollController: itemScrollController,
   itemPositionsListener: itemPositionsListener,
+  scrollOffsetListener: scrollOffsetListener,
 );
 ```
 
@@ -46,6 +48,15 @@ One can monitor what items are visible on screen with:
 itemPositionsListener.itemPositions.addListener(() => ...);
 ```
 
+Changes in scroll position can be monitored with:
+
+```dart
+scrollOffsetListener.changes.listen((event) => ...)
+```
+
+see `ScrollSum` in [this test](test/scroll_offset_listener_test.dart) for an example of how the current offset can be 
+calculated from the stream of scroll change deltas.  This feature is new and experimental.
+
 A full example can be found in the example folder.
 
 --------------------------------------------------------------------------------

packages/scrollable_positioned_list/pubspec.yaml

@@ -1,5 +1,5 @@
 name: scrollable_positioned_list
-version: 0.3.6
+version: 0.3.7
 description: >
   A list with helper methods to programmatically scroll to an item.
 homepage: https://github.com/google/flutter.widgets/tree/master/packages/scrollable_positioned_list