[Gallery] Close Shrine cart on back button press for android (#288)

* Close Shrine cart on back button press for android

gallery/gallery/lib/studies/shrine/app.dart

@@ -78,6 +78,18 @@ class _ShrineAppState extends State<ShrineApp> with TickerProviderStateMixin {
     );
   }
 
+  // Closes the bottom sheet if it is open.
+  Future<bool> _onWillPop() async {
+    final status = _expandingController.status;
+    if (status == AnimationStatus.completed ||
+        status == AnimationStatus.forward) {
+      _expandingController.reverse();
+      return false;
+    }
+
+    return true;
+  }
+
   @override
   Widget build(BuildContext context) {
     final bool isDesktop = isDisplayDesktop(context);
@@ -86,6 +98,8 @@ class _ShrineAppState extends State<ShrineApp> with TickerProviderStateMixin {
 
     return ScopedModel<AppStateModel>(
       model: _model,
+      child: WillPopScope(
+        onWillPop: _onWillPop,
         child: MaterialApp(
           navigatorKey: widget.navigatorKey,
           title: 'Shrine',
@@ -115,6 +129,7 @@ class _ShrineAppState extends State<ShrineApp> with TickerProviderStateMixin {
           supportedLocales: GalleryLocalizations.supportedLocales,
           locale: GalleryOptions.of(context).locale,
         ),
+      ),
     );
   }
 }

gallery/gallery/lib/studies/shrine/expanding_bottom_sheet.dart

@@ -2,11 +2,9 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:math';
 
 import 'package:flutter/material.dart';
-import 'package:flutter/services.dart';
 import 'package:meta/meta.dart';
 import 'package:scoped_model/scoped_model.dart';
 
@@ -51,11 +49,11 @@ double _paddedThumbnailHeight(BuildContext context) {
 }
 
 class ExpandingBottomSheet extends StatefulWidget {
-  const ExpandingBottomSheet(
+  const ExpandingBottomSheet({
-      {Key key,
+    Key key,
     @required this.hideController,
-      @required this.expandingController})
+    @required this.expandingController,
-      : assert(hideController != null),
+  })  : assert(hideController != null),
         assert(expandingController != null),
         super(key: key);
 
@@ -551,18 +549,6 @@ class _ExpandingBottomSheetState extends State<ExpandingBottomSheet>
     }
   }
 
-  // Closes the cart if the cart is open, otherwise exits the app (this should
-  // only be relevant for Android).
-  Future<bool> _onWillPop() async {
-    if (!_isOpen) {
-      await SystemNavigator.pop();
-      return true;
-    }
-
-    close();
-    return true;
-  }
-
   @override
   Widget build(BuildContext context) {
     return AnimatedSize(
@@ -571,8 +557,6 @@ class _ExpandingBottomSheetState extends State<ExpandingBottomSheet>
       curve: Curves.easeInOut,
       vsync: this,
       alignment: AlignmentDirectional.topStart,
-      child: WillPopScope(
-        onWillPop: _onWillPop,
       child: AnimatedBuilder(
         animation: widget.hideController,
         builder: (context, child) => AnimatedBuilder(
@@ -583,7 +567,6 @@ class _ExpandingBottomSheetState extends State<ExpandingBottomSheet>
           ),
         ),
       ),
-      ),
     );
   }
 }