Ignore pointer scrolls on viewports that have no content dimensions yet

Fixes #1338

Author: rolandgeider

lib/core/widgets/scroll_behavior.dart

@@ -0,0 +1,47 @@
+/*
+ * This file is part of wger Workout Manager <https://github.com/wger-project>.
+ * Copyright (c) 2026 - 2026 wger Team
+ *
+ * wger Workout Manager is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+import 'package:flutter/material.dart';
+
+/// Ignores mouse wheel and trackpad scrolls until the viewport has content
+/// dimensions. The framework reads them unguarded, so a scroll that lands on a
+/// not-yet-laid-out list would otherwise crash with a null check.
+class LaidOutScrollPhysics extends ScrollPhysics {
+  const LaidOutScrollPhysics({super.parent});
+
+  @override
+  LaidOutScrollPhysics applyTo(ScrollPhysics? ancestor) {
+    return LaidOutScrollPhysics(parent: buildParent(ancestor));
+  }
+
+  @override
+  bool shouldAcceptUserOffset(ScrollMetrics position) {
+    return position.hasContentDimensions && super.shouldAcceptUserOffset(position);
+  }
+}
+
+/// App-wide scroll behavior: the platform default physics wrapped in
+/// [LaidOutScrollPhysics].
+class WgerScrollBehavior extends MaterialScrollBehavior {
+  const WgerScrollBehavior();
+
+  @override
+  ScrollPhysics getScrollPhysics(BuildContext context) {
+    return const LaidOutScrollPhysics().applyTo(super.getScrollPhysics(context));
+  }
+}

lib/main.dart

@@ -48,6 +48,7 @@ import 'package:wger/core/update_app_screen.dart';
 import 'package:wger/core/update_server_screen.dart';
 import 'package:wger/core/widgets/about.dart';
 import 'package:wger/core/widgets/log_overview.dart';
+import 'package:wger/core/widgets/scroll_behavior.dart';
 import 'package:wger/features/account/widgets/settings.dart';
 import 'package:wger/features/auth/screens/auth_screen.dart';
 import 'package:wger/features/auth/screens/auto_login_error_screen.dart';
@@ -240,12 +241,14 @@ class MainApp extends ConsumerWidget {
 
         return authAsync.when(
           loading: () => MaterialApp(
+            scrollBehavior: const WgerScrollBehavior(),
             theme: light,
             darkTheme: dark,
             themeMode: themeMode,
             home: const SplashScreen(),
           ),
           error: (error, stack) => MaterialApp(
+            scrollBehavior: const WgerScrollBehavior(),
             theme: light,
             darkTheme: dark,
             themeMode: themeMode,
@@ -258,6 +261,7 @@ class MainApp extends ConsumerWidget {
               title: 'wger',
               navigatorKey: navigatorKey,
               scaffoldMessengerKey: scaffoldMessengerKey,
+              scrollBehavior: const WgerScrollBehavior(),
               theme: light,
               darkTheme: dark,
               highContrastTheme: lightHc,

test/core/widgets/scroll_behavior_test.dart

@@ -0,0 +1,73 @@
+/*
+ * This file is part of wger Workout Manager <https://github.com/wger-project>.
+ * Copyright (c) 2026 - 2026 wger Team
+ *
+ * wger Workout Manager is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:wger/core/widgets/scroll_behavior.dart';
+
+void main() {
+  ScrollMetrics metrics({double? minExtent, double? maxExtent, double? pixels}) {
+    return FixedScrollMetrics(
+      minScrollExtent: minExtent,
+      maxScrollExtent: maxExtent,
+      pixels: pixels,
+      viewportDimension: 100,
+      axisDirection: AxisDirection.down,
+      devicePixelRatio: 1,
+    );
+  }
+
+  group('LaidOutScrollPhysics', () {
+    const physics = LaidOutScrollPhysics();
+
+    test('rejects user offsets before the viewport has content dimensions', () {
+      expect(physics.shouldAcceptUserOffset(metrics()), isFalse);
+    });
+
+    test('delegates to the parent once laid out', () {
+      final chained = physics.applyTo(const ClampingScrollPhysics());
+
+      expect(
+        chained.shouldAcceptUserOffset(metrics(minExtent: 0, maxExtent: 50, pixels: 0)),
+        isTrue,
+      );
+      expect(
+        chained.shouldAcceptUserOffset(metrics(minExtent: 0, maxExtent: 0, pixels: 0)),
+        isFalse,
+      );
+    });
+  });
+
+  testWidgets('WgerScrollBehavior wraps the platform physics', (tester) async {
+    late ScrollPhysics physics;
+    await tester.pumpWidget(
+      MaterialApp(
+        scrollBehavior: const WgerScrollBehavior(),
+        home: Builder(
+          builder: (context) {
+            physics = ScrollConfiguration.of(context).getScrollPhysics(context);
+            return const SizedBox();
+          },
+        ),
+      ),
+    );
+
+    expect(physics, isA<LaidOutScrollPhysics>());
+    expect(physics.parent, isNotNull);
+  });
+}