🥅 More exception info

Author: AlexV525

lib/src/delegates/asset_picker_builder_delegate.dart

@@ -967,40 +967,59 @@ class DefaultAssetPickerBuilderDelegate
       return;
     }
     final revert = effectiveShouldRevertGrid(context);
-    List<AssetEntity> current;
+    // ignore: no_leading_underscores_for_local_identifiers
+    final int _debugFlow; // Only for debug process.
+    final List<AssetEntity> current;
     final List<AssetEntity>? selected;
     final int effectiveIndex;
     if (isWeChatMoment) {
       if (currentAsset.type == AssetType.video) {
         current = <AssetEntity>[currentAsset];
         selected = null;
         effectiveIndex = 0;
+        _debugFlow = 10;
       } else {
+        final List<AssetEntity> list;
         if (index == null) {
-          current = p.selectedAssets;
-          current = current.reversed.toList(growable: false);
+          list = p.selectedAssets.reversed.toList(growable: false);
         } else {
-          current = p.currentAssets;
+          list = p.currentAssets;
         }
-        current = current
-            .where((AssetEntity e) => e.type == AssetType.image)
-            .toList();
+        current = list.where((e) => e.type == AssetType.image).toList();
         selected = p.selectedAssets;
         final i = current.indexOf(currentAsset);
         effectiveIndex = revert ? current.length - i - 1 : i;
+        _debugFlow = switch ((index == null, revert)) {
+          (true, true) => 21,
+          (true, false) => 20,
+          (false, true) => 31,
+          (false, false) => 30,
+        };
       }
     } else {
       selected = p.selectedAssets;
+      final List<AssetEntity> list;
       if (index == null) {
-        current = p.selectedAssets;
         if (revert) {
-          current = current.reversed.toList(growable: false);
+          list = p.selectedAssets.reversed.toList(growable: false);
+        } else {
+          list = p.selectedAssets;
         }
         effectiveIndex = selected.indexOf(currentAsset);
+        current = list;
       } else {
         current = p.currentAssets;
         effectiveIndex = revert ? current.length - index - 1 : index;
       }
+      _debugFlow = switch ((index == null, revert)) {
+        (true, true) => 41,
+        (true, false) => 40,
+        (false, true) => 51,
+        (false, false) => 50,
+      };
+    }
+    if (current.isEmpty) {
+      throw StateError('Previewing empty assets is not allowed. $_debugFlow');
     }
     final List<AssetEntity>? result = await AssetPickerViewer.pushToViewer(
       context,

lib/src/delegates/asset_picker_viewer_builder_delegate.dart

@@ -39,8 +39,9 @@ abstract class AssetPickerViewerBuilderDelegate<Asset, Path> {
     this.maxAssets,
     this.shouldReversePreview = false,
     this.selectPredicate,
-  })  : assert(maxAssets == null || maxAssets > 0),
-        assert(currentIndex >= 0);
+  })  : assert(previewAssets.isNotEmpty),
+        assert(currentIndex >= 0),
+        assert(maxAssets == null || maxAssets > 0);
 
   /// [ChangeNotifier] for photo selector viewer.
   /// 资源预览器的状态保持

lib/src/widget/asset_picker_viewer.dart

@@ -45,6 +45,9 @@ class AssetPickerViewer<Asset, Path> extends StatefulWidget {
         const PermissionRequestOption(),
     bool shouldAutoplayPreview = false,
   }) async {
+    if (previewAssets.isEmpty) {
+      throw StateError('Previewing empty assets is not allowed.');
+    }
     await AssetPicker.permissionCheck(requestOption: permissionRequestOption);
     final Widget viewer = AssetPickerViewer<AssetEntity, AssetPathEntity>(
       builder: DefaultAssetPickerViewerBuilderDelegate(