Initial code

.gitignore

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+# Miscellaneous
+*.class
+*.log
+*.pyc
+*.swp
+.DS_Store
+.atom/
+.buildlog/
+.history
+.svn/
+
+# IntelliJ related
+*.iml
+*.ipr
+*.iws
+.idea/
+
+# The .vscode folder contains launch configuration and tasks you configure in
+# VS Code which you may wish to be included in version control, so this line
+# is commented out by default.
+#.vscode/
+
+# Flutter/Dart/Pub related
+**/doc/api/
+.dart_tool/
+.flutter-plugins
+.flutter-plugins-dependencies
+.packages
+.pub-cache/
+.pub/
+build/
+
+# Android related
+**/android/**/gradle-wrapper.jar
+**/android/.gradle
+**/android/captures/
+**/android/gradlew
+**/android/gradlew.bat
+**/android/local.properties
+**/android/**/GeneratedPluginRegistrant.java
+
+# iOS/XCode related
+**/ios/**/*.mode1v3
+**/ios/**/*.mode2v3
+**/ios/**/*.moved-aside
+**/ios/**/*.pbxuser
+**/ios/**/*.perspectivev3
+**/ios/**/*sync/
+**/ios/**/.sconsign.dblite
+**/ios/**/.tags*
+**/ios/**/.vagrant/
+**/ios/**/DerivedData/
+**/ios/**/Icon?
+**/ios/**/Pods/
+**/ios/**/.symlinks/
+**/ios/**/profile
+**/ios/**/xcuserdata
+**/ios/.generated/
+**/ios/Flutter/App.framework
+**/ios/Flutter/Flutter.framework
+**/ios/Flutter/Flutter.podspec
+**/ios/Flutter/Generated.xcconfig
+**/ios/Flutter/ephemeral
+**/ios/Flutter/app.flx
+**/ios/Flutter/app.zip
+**/ios/Flutter/flutter_assets/
+**/ios/Flutter/flutter_export_environment.sh
+**/ios/ServiceDefinitions.json
+**/ios/Runner/GeneratedPluginRegistrant.*
+
+# Exceptions to above rules.
+!**/ios/**/default.mode1v3
+!**/ios/**/default.mode2v3
+!**/ios/**/default.pbxuser
+!**/ios/**/default.perspectivev3

.metadata

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+# This file tracks properties of this Flutter project.
+# Used by Flutter tool to assess capabilities and perform upgrades etc.
+#
+# This file should be version controlled and should not be manually edited.
+
+version:
+  revision: 18116933e77adc82f80866c928266a5b4f1ed645
+  channel: unknown
+
+project_type: package

CHANGELOG.md

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+## 0.0.1
+
+* TODO: Describe initial release.

LICENSE

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+TODO: Add your license here.

README.md

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+<!-- 
+This README describes the package. If you publish this package to pub.dev,
+this README's contents appear on the landing page for your package.
+
+For information about how to write a good package README, see the guide for
+[writing package pages](https://dart.dev/guides/libraries/writing-package-pages). 
+
+For general information about developing packages, see the Dart guide for
+[creating packages](https://dart.dev/guides/libraries/create-library-packages)
+and the Flutter guide for
+[developing packages and plugins](https://flutter.dev/developing-packages). 
+-->
+
+TODO: Put a short description of the package here that helps potential users
+know whether this package might be useful for them.
+
+## Features
+
+TODO: List what your package can do. Maybe include images, gifs, or videos.
+
+## Getting started
+
+TODO: List prerequisites and provide or point to information on how to
+start using the package.
+
+## Usage
+
+TODO: Include short and useful examples for package users. Add longer examples
+to `/example` folder. 
+
+```dart
+const like = 'sample';
+```
+
+## Additional information
+
+TODO: Tell users more about the package: where to find more information, how to 
+contribute to the package, how to file issues, what response they can expect 
+from the package authors, and more.

analysis_options.yaml

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+include: package:flutter_lints/flutter.yaml
+
+# Additional information about this file can be found at
+# https://dart.dev/guides/language/analysis-options

lib/autoscale_tabbarview.dart

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+library autoscale_tabbarview;
+
+export 'src/autoscale_tabbar_widget.dart';
+export 'src/sized_pageview.dart';
+export 'src/size_detector_widget.dart';

lib/src/autoscale_tabbar_widget.dart

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+import 'package:flutter/gestures.dart';
+import 'package:flutter/material.dart';
+
+import 'sized_pageview.dart';
+
+class AutoScaleTabBarView extends StatefulWidget {
+  /// Creates a page view with one child per tab.
+  ///
+  /// The length of [children] must be the same as the [controller]'s length.
+  const AutoScaleTabBarView({
+    Key? key,
+    required this.children,
+    this.controller,
+    this.physics,
+    this.dragStartBehavior = DragStartBehavior.start,
+  })  : assert(children != null),
+        assert(dragStartBehavior != null),
+        super(key: key);
+
+  /// This widget's selection and animation state.
+  ///
+  /// If [TabController] is not provided, then the value of [DefaultTabController.of]
+  /// will be used.
+  final TabController? controller;
+
+  /// One widget per tab.
+  ///
+  /// Its length must match the length of the [TabBar.tabs]
+  /// list, as well as the [controller]'s [TabController.length].
+  final List<Widget> children;
+
+  /// How the page view should respond to user input.
+  ///
+  /// For example, determines how the page view continues to animate after the
+  /// user stops dragging the page view.
+  ///
+  /// The physics are modified to snap to page boundaries using
+  /// [PageScrollPhysics] prior to being used.
+  ///
+  /// Defaults to matching platform conventions.
+  final ScrollPhysics? physics;
+
+  /// {@macro flutter.widgets.scrollable.dragStartBehavior}
+  final DragStartBehavior dragStartBehavior;
+
+  @override
+  State<AutoScaleTabBarView> createState() => _AutoScaleTabBarViewState();
+}
+
+class _AutoScaleTabBarViewState extends State<AutoScaleTabBarView> {
+  TabController? _controller;
+  late PageController _pageController;
+  late List<Widget> _children;
+  late List<Widget> _childrenWithKey;
+  int? _currentIndex;
+  int _warpUnderwayCount = 0;
+
+  // If the TabBarView is rebuilt with a new tab controller, the caller should
+  // dispose the old one. In that case the old controller's animation will be
+  // null and should not be accessed.
+  bool get _controllerIsValid => _controller?.animation != null;
+
+  void _updateTabController() {
+    final TabController? newController =
+        widget.controller ?? DefaultTabController.of(context);
+    assert(() {
+      if (newController == null) {
+        throw FlutterError(
+          'No TabController for ${widget.runtimeType}.\n'
+          'When creating a ${widget.runtimeType}, you must either provide an explicit '
+          'TabController using the "controller" property, or you must ensure that there '
+          'is a DefaultTabController above the ${widget.runtimeType}.\n'
+          'In this case, there was neither an explicit controller nor a default controller.',
+        );
+      }
+      return true;
+    }());
+
+    if (newController == _controller) return;
+
+    if (_controllerIsValid)
+      _controller!.animation!.removeListener(_handleTabControllerAnimationTick);
+    _controller = newController;
+    if (_controller != null)
+      _controller!.animation!.addListener(_handleTabControllerAnimationTick);
+  }
+
+  @override
+  void initState() {
+    super.initState();
+    _updateChildren();
+  }
+
+  @override
+  void didChangeDependencies() {
+    super.didChangeDependencies();
+    _updateTabController();
+    _currentIndex = _controller?.index;
+    _pageController = PageController(initialPage: _currentIndex ?? 0);
+  }
+
+  @override
+  void didUpdateWidget(AutoScaleTabBarView oldWidget) {
+    super.didUpdateWidget(oldWidget);
+    if (widget.controller != oldWidget.controller) _updateTabController();
+    if (widget.children != oldWidget.children && _warpUnderwayCount == 0)
+      _updateChildren();
+  }
+
+  @override
+  void dispose() {
+    if (_controllerIsValid)
+      _controller!.animation!.removeListener(_handleTabControllerAnimationTick);
+    _controller = null;
+    // We don't own the _controller Animation, so it's not disposed here.
+    super.dispose();
+  }
+
+  void _updateChildren() {
+    _children = widget.children;
+    _childrenWithKey = KeyedSubtree.ensureUniqueKeysForList(widget.children);
+  }
+
+  void _handleTabControllerAnimationTick() {
+    if (_warpUnderwayCount > 0 || !_controller!.indexIsChanging)
+      return; // This widget is driving the controller's animation.
+
+    if (_controller!.index != _currentIndex) {
+      _currentIndex = _controller!.index;
+      _warpToCurrentIndex();
+    }
+  }
+
+  Future<void> _warpToCurrentIndex() async {
+    if (!mounted) return Future<void>.value();
+
+    if (_pageController.page == _currentIndex!.toDouble())
+      return Future<void>.value();
+
+    final int previousIndex = _controller!.previousIndex;
+    if ((_currentIndex! - previousIndex).abs() == 1) {
+      _warpUnderwayCount += 1;
+      await _pageController.animateToPage(_currentIndex!,
+          duration: kTabScrollDuration, curve: Curves.ease);
+      _warpUnderwayCount -= 1;
+      return Future<void>.value();
+    }
+
+    assert((_currentIndex! - previousIndex).abs() > 1);
+    final int initialPage = _currentIndex! > previousIndex
+        ? _currentIndex! - 1
+        : _currentIndex! + 1;
+    final List<Widget> originalChildren = _childrenWithKey;
+    setState(() {
+      _warpUnderwayCount += 1;
+
+      _childrenWithKey = List<Widget>.from(_childrenWithKey, growable: false);
+      final Widget temp = _childrenWithKey[initialPage];
+      _childrenWithKey[initialPage] = _childrenWithKey[previousIndex];
+      _childrenWithKey[previousIndex] = temp;
+    });
+    _pageController.jumpToPage(initialPage);
+
+    await _pageController.animateToPage(_currentIndex!,
+        duration: kTabScrollDuration, curve: Curves.ease);
+    if (!mounted) return Future<void>.value();
+    setState(() {
+      _warpUnderwayCount -= 1;
+      if (widget.children != _children) {
+        _updateChildren();
+      } else {
+        _childrenWithKey = originalChildren;
+      }
+    });
+  }
+
+  // Called when the PageView scrolls
+  bool _handleScrollNotification(ScrollNotification notification) {
+    if (_warpUnderwayCount > 0) return false;
+
+    if (notification.depth != 0) return false;
+
+    _warpUnderwayCount += 1;
+    if (notification is ScrollUpdateNotification &&
+        !_controller!.indexIsChanging) {
+      if ((_pageController.page! - _controller!.index).abs() > 1.0) {
+        _controller!.index = _pageController.page!.floor();
+        _currentIndex = _controller!.index;
+      }
+      _controller!.offset =
+          (_pageController.page! - _controller!.index).clamp(-1.0, 1.0);
+    } else if (notification is ScrollEndNotification) {
+      _controller!.index = _pageController.page!.round();
+      _currentIndex = _controller!.index;
+      if (!_controller!.indexIsChanging) {
+        _controller!.offset =
+            (_pageController.page! - _controller!.index).clamp(-1.0, 1.0);
+      }
+    }
+    _warpUnderwayCount -= 1;
+
+    return false;
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    assert(() {
+      if (_controller!.length != widget.children.length) {
+        throw FlutterError(
+          "Controller's length property (${_controller!.length}) does not match the "
+          "number of tabs (${widget.children.length}) present in TabBar's tabs property.",
+        );
+      }
+      return true;
+    }());
+    return NotificationListener<ScrollNotification>(
+      onNotification: _handleScrollNotification,
+      child: SizedPageView(
+        dragStartBehavior: widget.dragStartBehavior,
+        pageController: _pageController,
+        physics: widget.physics == null
+            ? const PageScrollPhysics().applyTo(const ClampingScrollPhysics())
+            : const PageScrollPhysics().applyTo(widget.physics),
+        children: _childrenWithKey,
+      ),
+    );
+  }
+}

lib/src/size_detector_widget.dart

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+import 'package:flutter/material.dart';
+import 'package:flutter/scheduler.dart';
+
+class SizeDetectorWidget extends StatefulWidget {
+  final Widget child;
+  final ValueChanged<Size> onSizeDetect;
+
+  const SizeDetectorWidget({
+    Key? key,
+    required this.child,
+    required this.onSizeDetect,
+  }) : super(key: key);
+
+  @override
+  _SizeDetectorWidgetState createState() => _SizeDetectorWidgetState();
+}
+
+class _SizeDetectorWidgetState extends State<SizeDetectorWidget> {
+  Size? _oldSize;
+
+  @override
+  void initState() {
+    super.initState();
+    SchedulerBinding.instance?.addPostFrameCallback((_) => _detectSize());
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return widget.child;
+  }
+
+  void _detectSize() {
+    if (!mounted) {
+      return;
+    }
+    final size = context.size;
+    if (_oldSize != size) {
+      _oldSize = size;
+      widget.onSizeDetect(size!);
+    }
+  }
+}

lib/src/sized_pageview.dart

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+import 'package:flutter/gestures.dart';
+import 'package:flutter/material.dart';
+
+import 'size_detector_widget.dart';
+
+class SizedPageView extends StatefulWidget {
+  final List<Widget> children;
+  final PageController pageController;
+  final DragStartBehavior dragStartBehavior;
+  final ScrollPhysics physics;
+
+  const SizedPageView({
+    Key? key,
+    required this.children,
+    required this.pageController,
+    required this.dragStartBehavior,
+    required this.physics,
+  }) : super(key: key);
+
+  @override
+  _SizedPageViewState createState() => _SizedPageViewState();
+}
+
+class _SizedPageViewState extends State<SizedPageView>
+    with SingleTickerProviderStateMixin {
+  late List<double> _heights;
+  int _currentIndex = 0;
+
+  double get _currentHeight => _heights[_currentIndex];
+
+  @override
+  void initState() {
+    super.initState();
+    _heights = List.generate(widget.children.length, (index) => 0.0);
+
+    widget.pageController.addListener(() {
+      final _newIndex = widget.pageController.page?.round();
+      if (_currentIndex != _newIndex) {
+        if (!mounted) {
+          return;
+        }
+        setState(() => _currentIndex = _newIndex!);
+      }
+    });
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return TweenAnimationBuilder<double>(
+      curve: Curves.easeInOutCubic,
+      duration: const Duration(milliseconds: 100),
+      tween: Tween<double>(begin: _heights[0], end: _currentHeight),
+      builder: (context, value, child) => SizedBox(height: value, child: child),
+      child: PageView(
+        controller: widget.pageController,
+        physics: widget.physics,
+        dragStartBehavior: widget.dragStartBehavior,
+        children: List.generate(widget.children.length, (index) {
+          return OverflowBox(
+            maxHeight: double.infinity,
+            alignment: Alignment.topCenter,
+            child: SizeDetectorWidget(
+              onSizeDetect: (size) {
+                if (mounted) {
+                  setState(() => _heights[index] = size.height);
+                }
+              },
+              child: Align(child: widget.children[index]),
+            ),
+          );
+        }),
+      ),
+    );
+  }
+
+  @override
+  void dispose() {
+    widget.pageController.dispose();
+    super.dispose();
+  }
+}

pubspec.lock

@@ -0,0 +1,161 @@
+# Generated by pub
+# See https://dart.dev/tools/pub/glossary#lockfile
+packages:
+  async:
+    dependency: transitive
+    description:
+      name: async
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "2.8.1"
+  boolean_selector:
+    dependency: transitive
+    description:
+      name: boolean_selector
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "2.1.0"
+  characters:
+    dependency: transitive
+    description:
+      name: characters
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "1.1.0"
+  charcode:
+    dependency: transitive
+    description:
+      name: charcode
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "1.3.1"
+  clock:
+    dependency: transitive
+    description:
+      name: clock
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "1.1.0"
+  collection:
+    dependency: transitive
+    description:
+      name: collection
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "1.15.0"
+  fake_async:
+    dependency: transitive
+    description:
+      name: fake_async
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "1.2.0"
+  flutter:
+    dependency: "direct main"
+    description: flutter
+    source: sdk
+    version: "0.0.0"
+  flutter_lints:
+    dependency: "direct dev"
+    description:
+      name: flutter_lints
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "1.0.4"
+  flutter_test:
+    dependency: "direct dev"
+    description: flutter
+    source: sdk
+    version: "0.0.0"
+  lints:
+    dependency: transitive
+    description:
+      name: lints
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "1.0.1"
+  matcher:
+    dependency: transitive
+    description:
+      name: matcher
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "0.12.10"
+  meta:
+    dependency: transitive
+    description:
+      name: meta
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "1.7.0"
+  path:
+    dependency: transitive
+    description:
+      name: path
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "1.8.0"
+  sky_engine:
+    dependency: transitive
+    description: flutter
+    source: sdk
+    version: "0.0.99"
+  source_span:
+    dependency: transitive
+    description:
+      name: source_span
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "1.8.1"
+  stack_trace:
+    dependency: transitive
+    description:
+      name: stack_trace
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "1.10.0"
+  stream_channel:
+    dependency: transitive
+    description:
+      name: stream_channel
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "2.1.0"
+  string_scanner:
+    dependency: transitive
+    description:
+      name: string_scanner
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "1.1.0"
+  term_glyph:
+    dependency: transitive
+    description:
+      name: term_glyph
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "1.2.0"
+  test_api:
+    dependency: transitive
+    description:
+      name: test_api
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "0.4.2"
+  typed_data:
+    dependency: transitive
+    description:
+      name: typed_data
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "1.3.0"
+  vector_math:
+    dependency: transitive
+    description:
+      name: vector_math
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "2.1.0"
+sdks:
+  dart: ">=2.12.0 <3.0.0"
+  flutter: ">=1.17.0"

pubspec.yaml

@@ -0,0 +1,54 @@
+name: autoscale_tabbarview
+description: A new Flutter package project.
+version: 0.0.1
+homepage:
+
+environment:
+  sdk: ">=2.12.0 <3.0.0"
+  flutter: ">=1.17.0"
+
+dependencies:
+  flutter:
+    sdk: flutter
+
+dev_dependencies:
+  flutter_test:
+    sdk: flutter
+  flutter_lints: ^1.0.0
+
+# For information on the generic Dart part of this file, see the
+# following page: https://dart.dev/tools/pub/pubspec
+
+# The following section is specific to Flutter.
+flutter:
+
+  # To add assets to your package, add an assets section, like this:
+  # assets:
+  #   - images/a_dot_burr.jpeg
+  #   - images/a_dot_ham.jpeg
+  #
+  # For details regarding assets in packages, see
+  # https://flutter.dev/assets-and-images/#from-packages
+  #
+  # An image asset can refer to one or more resolution-specific "variants", see
+  # https://flutter.dev/assets-and-images/#resolution-aware.
+
+  # To add custom fonts to your package, add a fonts section here,
+  # in this "flutter" section. Each entry in this list should have a
+  # "family" key with the font family name, and a "fonts" key with a
+  # list giving the asset and other descriptors for the font. For
+  # example:
+  # fonts:
+  #   - family: Schyler
+  #     fonts:
+  #       - asset: fonts/Schyler-Regular.ttf
+  #       - asset: fonts/Schyler-Italic.ttf
+  #         style: italic
+  #   - family: Trajan Pro
+  #     fonts:
+  #       - asset: fonts/TrajanPro.ttf
+  #       - asset: fonts/TrajanPro_Bold.ttf
+  #         weight: 700
+  #
+  # For details regarding fonts in packages, see
+  # https://flutter.dev/custom-fonts/#from-packages