flutter/examples/api/lib/widgets/page_view/page_view.0.dart

// Copyright 2014 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';

/// Flutter code sample for [PageView].

void main() => runApp(const PageViewExampleApp());

class PageViewExampleApp extends StatelessWidget {
  const PageViewExampleApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: const Text('PageView Sample')),
        body: const PageViewExample(),
      ),
    );
  }
}

class PageViewExample extends StatefulWidget {
  const PageViewExample({super.key});

  @override
  State<PageViewExample> createState() => _PageViewExampleState();
}

class _PageViewExampleState extends State<PageViewExample> with TickerProviderStateMixin {
  late PageController _pageViewController;
  late TabController _tabController;
  int _currentPageIndex = 0;

  @override
  void initState() {
    super.initState();
    _pageViewController = PageController();
    _tabController = TabController(length: 3, vsync: this);
  }

  @override
  void dispose() {
    super.dispose();
    _pageViewController.dispose();
    _tabController.dispose();
  }

  @override
  Widget build(BuildContext context) {
    final TextTheme textTheme = Theme.of(context).textTheme;

    return Stack(
      alignment: Alignment.bottomCenter,
      children: <Widget>[
        PageView(
          /// [PageView.scrollDirection] defaults to [Axis.horizontal].
          /// Use [Axis.vertical] to scroll vertically.
          controller: _pageViewController,
          onPageChanged: _handlePageViewChanged,
          children: <Widget>[
            Center(
              child: Text('First Page', style: textTheme.titleLarge),
            ),
            Center(
              child: Text('Second Page', style: textTheme.titleLarge),
            ),
            Center(
              child: Text('Third Page', style: textTheme.titleLarge),
            ),
          ],
        ),
        PageIndicator(
          tabController: _tabController,
          currentPageIndex: _currentPageIndex,
          onUpdateCurrentPageIndex: _updateCurrentPageIndex,
          isOnDesktopAndWeb: _isOnDesktopAndWeb,
        ),
      ],
    );
  }

  void _handlePageViewChanged(int currentPageIndex) {
    if (!_isOnDesktopAndWeb) {
      return;
    }
    _tabController.index = currentPageIndex;
    setState(() {
      _currentPageIndex = currentPageIndex;
    });
  }

  void _updateCurrentPageIndex(int index) {
    _tabController.index = index;
    _pageViewController.animateToPage(
      index,
      duration: const Duration(milliseconds: 400),
      curve: Curves.easeInOut,
    );
  }

  bool get _isOnDesktopAndWeb {
    if (kIsWeb) {
      return true;
    }
    switch (defaultTargetPlatform) {
      case TargetPlatform.macOS:
      case TargetPlatform.linux:
      case TargetPlatform.windows:
        return true;
      case TargetPlatform.android:
      case TargetPlatform.iOS:
      case TargetPlatform.fuchsia:
        return false;
    }
  }
}

/// Page indicator for desktop and web platforms.
///
/// On Desktop and Web, drag gesture for horizontal scrolling in a PageView is disabled by default.
/// You can defined a custom scroll behavior to activate drag gestures,
/// see https://docs.flutter.dev/release/breaking-changes/default-scroll-behavior-drag.
///
/// In this sample, we use a TabPageSelector to navigate between pages,
/// in order to build natural behavior similar to other desktop applications.
class PageIndicator extends StatelessWidget {
  const PageIndicator({
    super.key,
    required this.tabController,
    required this.currentPageIndex,
    required this.onUpdateCurrentPageIndex,
    required this.isOnDesktopAndWeb,
  });

  final int currentPageIndex;
  final TabController tabController;
  final void Function(int) onUpdateCurrentPageIndex;
  final bool isOnDesktopAndWeb;

  @override
  Widget build(BuildContext context) {
    if (!isOnDesktopAndWeb) {
      return const SizedBox.shrink();
    }
    final ColorScheme colorScheme = Theme.of(context).colorScheme;

    return Padding(
      padding: const EdgeInsets.all(8.0),
      child: Row(
        mainAxisAlignment: MainAxisAlignment.center,
        children: <Widget>[
          IconButton(
            splashRadius: 16.0,
            padding: EdgeInsets.zero,
            onPressed: () {
              if (currentPageIndex == 0) {
                return;
              }
              onUpdateCurrentPageIndex(currentPageIndex - 1);
            },
            icon: const Icon(
              Icons.arrow_left_rounded,
              size: 32.0,
            ),
          ),
          TabPageSelector(
            controller: tabController,
            color: colorScheme.background,
            selectedColor: colorScheme.primary,
          ),
          IconButton(
            splashRadius: 16.0,
            padding: EdgeInsets.zero,
            onPressed: () {
              if (currentPageIndex == 2) {
                return;
              }
              onUpdateCurrentPageIndex(currentPageIndex + 1);
            },
            icon: const Icon(
              Icons.arrow_right_rounded,
              size: 32.0,
            ),
          ),
        ],
      ),
    );
  }
}