Cache photos to the left and right

lib/events/photo_opened_event.dart

@@ -0,0 +1,7 @@
+import 'package:photos/models/photo.dart';
+
+class PhotoOpenedEvent {
+  final Photo photo;
+
+  PhotoOpenedEvent(this.photo);
+}

lib/ui/detail_page.dart

@@ -1,8 +1,11 @@
 import 'package:flutter/cupertino.dart';
 import 'package:flutter/material.dart';
 import 'package:like_button/like_button.dart';
+import 'package:photos/core/event_bus.dart';
+import 'package:photos/events/photo_opened_event.dart';
 import 'package:photos/favorite_photos_repository.dart';
 import 'package:photos/models/photo.dart';
+import 'package:photos/ui/extents_page_view.dart';
 import 'package:photos/ui/zoomable_image.dart';
 import 'package:photos/utils/share_util.dart';
 import 'package:logging/logging.dart';
@@ -52,29 +55,35 @@ class _DetailPageState extends State<DetailPage> {
 
   Widget _buildPageView() {
     _pageController = PageController(initialPage: _selectedIndex);
-    return PageView.builder(
+    return ExtentsPageView.extents(
       itemBuilder: (context, index) {
         final photo = _photos[index];
-        final image = ZoomableImage(
+        final image = Hero(
+          tag: photo.hashCode,
+          child: ZoomableImage(
             photo,
             shouldDisableScroll: (value) {
               setState(() {
                 _shouldDisableScroll = value;
               });
             },
+          ),
         );
+        if (index == _selectedIndex) {
+          Bus.instance.fire(PhotoOpenedEvent(photo));
+        }
         return image;
       },
       onPageChanged: (int index) {
-        setState(() {
         _selectedIndex = index;
-        });
+        Bus.instance.fire(PhotoOpenedEvent(widget.photos[index]));
       },
       physics: _shouldDisableScroll
           ? NeverScrollableScrollPhysics()
           : PageScrollPhysics(),
       controller: _pageController,
       itemCount: _photos.length,
+      extents: 1,
     );
   }
 

lib/ui/gallery.dart

@@ -1,8 +1,11 @@
+import 'dart:async';
 import 'dart:collection';
 
 import 'package:flutter/cupertino.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
+import 'package:photos/core/event_bus.dart';
+import 'package:photos/events/photo_opened_event.dart';
 import 'package:photos/models/photo.dart';
 import 'package:photos/photo_sync_manager.dart';
 import 'package:photos/ui/detail_page.dart';
@@ -32,6 +35,24 @@ class _GalleryState extends State<Gallery> {
   List<Photo> _photos;
   RefreshController _refreshController =
       RefreshController(initialRefresh: false);
+  StreamSubscription<PhotoOpenedEvent> _subscription;
+  Photo _openedPhoto;
+
+  @override
+  void initState() {
+    _subscription = Bus.instance.on<PhotoOpenedEvent>().listen((event) {
+      setState(() {
+        _openedPhoto = event.photo;
+      });
+    });
+    super.initState();
+  }
+
+  @override
+  void dispose() {
+    _subscription.cancel();
+    super.dispose();
+  }
 
   @override
   Widget build(BuildContext context) {
@@ -127,10 +148,9 @@ class _GalleryState extends State<Gallery> {
               ? Border.all(width: 4.0, color: Colors.blue)
               : null,
         ),
-        child: Hero(
-          tag: photo.hashCode,
-          child: ThumbnailWidget(photo),
-        ),
+        child: photo == _openedPhoto
+            ? Hero(tag: photo.hashCode, child: ThumbnailWidget(photo))
+            : ThumbnailWidget(photo),
       ),
     );
   }

lib/ui/zoomable_image.dart

@@ -1,3 +1,4 @@
+import 'package:extended_image/extended_image.dart';
 import 'package:flutter/foundation.dart';
 import 'package:flutter/widgets.dart';
 import 'package:photos/core/cache/image_cache.dart';
@@ -21,7 +22,8 @@ class ZoomableImage extends StatefulWidget {
   _ZoomableImageState createState() => _ZoomableImageState();
 }
 
-class _ZoomableImageState extends State<ZoomableImage> {
+class _ZoomableImageState extends State<ZoomableImage>
+    with SingleTickerProviderStateMixin {
   ImageProvider _imageProvider;
   bool _loadedSmallThumbnail = false;
   bool _loadingLargeThumbnail = false;
@@ -29,6 +31,10 @@ class _ZoomableImageState extends State<ZoomableImage> {
   bool _loadingFinalImage = false;
   bool _loadedFinalImage = false;
   ValueChanged<PhotoViewScaleState> _scaleStateChangedCallback;
+  // AnimationController _animationController;
+  // Animation _animation;
+  // VoidCallback _animationListener;
+  final doubleTapScales = [1.0, 2.0];
 
   @override
   void initState() {
@@ -37,6 +43,10 @@ class _ZoomableImageState extends State<ZoomableImage> {
         widget.shouldDisableScroll(value != PhotoViewScaleState.initial);
       }
     };
+    // _animationController = AnimationController(
+    //   vsync: this,
+    //   duration: const Duration(milliseconds: 100),
+    // );
     super.initState();
   }
 
@@ -49,12 +59,46 @@ class _ZoomableImageState extends State<ZoomableImage> {
     }
 
     if (_imageProvider != null) {
+      // return ExtendedImage(
+      //   image: _imageProvider,
+      //   gaplessPlayback: true,
+      //   mode: ExtendedImageMode.gesture,
+      //   enableSlideOutPage: true,
+      //   initGestureConfigHandler: (state) {
+      //     return GestureConfig(
+      //       inPageView: true,
+      //       initialScale: 1.0,
+      //       minScale: 1.0,
+      //     );
+      //   },
+      //   onDoubleTap: (ExtendedImageGestureState state) {
+      //     var pointerDownPosition = state.pointerDownPosition;
+      //     double begin = state.gestureDetails.totalScale;
+      //     double end;
+      //     _animation?.removeListener(_animationListener);
+      //     _animationController.stop();
+      //     _animationController.reset();
+      //     if (begin == doubleTapScales[0]) {
+      //       end = doubleTapScales[1];
+      //     } else {
+      //       end = doubleTapScales[0];
+      //     }
+      //     _animationListener = () {
+      //       state.handleDoubleTap(
+      //           scale: _animation.value,
+      //           doubleTapPosition: pointerDownPosition);
+      //     };
+      //     _animation =
+      //         _animationController.drive(Tween<double>(begin: begin, end: end));
+      //     _animation.addListener(_animationListener);
+      //     _animationController.forward();
+      //   },
+      // );
       return PhotoView(
         imageProvider: _imageProvider,
         scaleStateChangedCallback: _scaleStateChangedCallback,
         minScale: PhotoViewComputedScale.contained,
         gaplessPlayback: true,
-        heroAttributes: PhotoViewHeroAttributes(tag: widget.photo.hashCode),
       );
     } else {
       return loadWidget;

pubspec.lock

@@ -36,6 +36,13 @@ packages:
       url: "https://pub.dartlang.org"
     source: hosted
     version: "1.1.3"
+  clock:
+    dependency: transitive
+    description:
+      name: clock
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "1.0.1"
   collection:
     dependency: transitive
     description:
@@ -120,6 +127,27 @@ packages:
       url: "https://pub.dartlang.org"
     source: hosted
     version: "1.1.1"
+  extended_image:
+    dependency: "direct main"
+    description:
+      name: extended_image
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "0.9.0"
+  extended_image_library:
+    dependency: transitive
+    description:
+      name: extended_image_library
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "0.2.3"
+  fake_async:
+    dependency: transitive
+    description:
+      name: fake_async
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "1.1.0"
   flutter:
     dependency: "direct main"
     description: flutter
@@ -191,6 +219,13 @@ packages:
       url: "https://pub.dartlang.org"
     source: hosted
     version: "0.12.1"
+  http_client_helper:
+    dependency: transitive
+    description:
+      name: http_client_helper
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "0.2.1"
   http_parser:
     dependency: transitive
     description:
@@ -267,7 +302,7 @@ packages:
       name: path
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.6.4"
+    version: "1.7.0"
   path_provider:
     dependency: "direct main"
     description:
@@ -345,13 +380,6 @@ packages:
       url: "https://pub.dartlang.org"
     source: hosted
     version: "1.5.8"
-  quiver:
-    dependency: transitive
-    description:
-      name: quiver
-      url: "https://pub.dartlang.org"
-    source: hosted
-    version: "2.1.3"
   sensors:
     dependency: transitive
     description:
@@ -475,7 +503,7 @@ packages:
       name: test_api
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.2.15"
+    version: "0.2.16"
   toast:
     dependency: "direct main"
     description:

pubspec.yaml

@@ -50,6 +50,7 @@ dependencies:
   flutter_typeahead: ^1.8.1
   pull_to_refresh: ^1.5.7
   fluttertoast: ^4.0.1
+  extended_image: ^0.9.0
 
 dev_dependencies:
   flutter_test: