🐛 Further fix to the wrong behavior in WeChat Moment video preview (#113)

Author: AlexV525

example/lib/pages/multi_assets_page.dart

@@ -49,7 +49,6 @@ class _MultiAssetsPageState extends State<MultiAssetsPage>
           return AssetPicker.pickAssets(
             context,
             maxAssets: maxAssetsCount,
-            selectedAssets: assets,
             specialPickerType: SpecialPickerType.wechatMoment,
           );
         },

lib/src/constants/custom_scroll_physics.dart

@@ -5,12 +5,34 @@
 import 'package:flutter/cupertino.dart';
 import 'package:flutter/physics.dart';
 
-class CustomScrollPhysics extends BouncingScrollPhysics {
-  const CustomScrollPhysics({ScrollPhysics? parent}) : super(parent: parent);
+class CustomBouncingScrollPhysics extends BouncingScrollPhysics {
+  const CustomBouncingScrollPhysics({
+    ScrollPhysics? parent,
+  }) : super(parent: parent);
 
   @override
-  CustomScrollPhysics applyTo(ScrollPhysics? ancestor) {
-    return CustomScrollPhysics(parent: buildParent(ancestor));
+  CustomBouncingScrollPhysics applyTo(ScrollPhysics? ancestor) {
+    return CustomBouncingScrollPhysics(parent: buildParent(ancestor));
+  }
+
+  @override
+  SpringDescription get spring {
+    return SpringDescription.withDampingRatio(
+      mass: 0.5,
+      stiffness: 400.0,
+      ratio: 1.1,
+    );
+  }
+}
+
+class CustomClampingScrollPhysics extends ClampingScrollPhysics {
+  const CustomClampingScrollPhysics({
+    ScrollPhysics? parent,
+  }) : super(parent: parent);
+
+  @override
+  CustomClampingScrollPhysics applyTo(ScrollPhysics? ancestor) {
+    return CustomClampingScrollPhysics(parent: buildParent(ancestor));
   }
 
   @override

lib/src/delegates/asset_picker_builder_delegate.dart

@@ -1250,12 +1250,12 @@ class DefaultAssetPickerBuilderDelegate
             return;
           }
           final List<AssetEntity> _current;
-          final List<AssetEntity> _selected;
+          final List<AssetEntity>? _selected;
           final int _index;
           if (isWeChatMoment) {
             if (asset.type == AssetType.video) {
               _current = <AssetEntity>[asset];
-              _selected = <AssetEntity>[];
+              _selected = null;
               _index = 0;
             } else {
               _current = provider.currentAssets

lib/src/delegates/asset_picker_viewer_builder_delegate.dart

@@ -754,7 +754,9 @@ class DefaultAssetPickerViewerBuilderDelegate
               children: <Widget>[
                 Positioned.fill(
                   child: ExtendedImageGesturePageView.builder(
-                    physics: const CustomScrollPhysics(),
+                    physics: previewAssets.length == 1
+                        ? const CustomClampingScrollPhysics()
+                        : const CustomBouncingScrollPhysics(),
                     controller: pageController,
                     itemCount: previewAssets.length,
                     itemBuilder: assetPageBuilder,