PageView example with dots indicator

main.dart

// Copyright 2017, the Flutter project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

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

void main() {
  runApp(new MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter Demo',
      home: new MyHomePage(),
      debugShowCheckedModeBanner: false,
    );
  }
}

/// An indicator showing the currently selected page of a PageController
class DotsIndicator extends AnimatedWidget {
  DotsIndicator({
    this.controller,
    this.itemCount,
    this.onPageSelected,
    this.color: Colors.white,
  }) : super(listenable: controller);

  /// The PageController that this DotsIndicator is representing.
  final PageController controller;

  /// The number of items managed by the PageController
  final int itemCount;

  /// Called when a dot is tapped
  final ValueChanged<int> onPageSelected;

  /// The color of the dots.
  ///
  /// Defaults to `Colors.white`.
  final Color color;

  // The base size of the dots
  static const double _kDotSize = 8.0;

  // The increase in the size of the selected dot
  static const double _kMaxZoom = 2.0;

  // The distance between the center of each dot
  static const double _kDotSpacing = 25.0;

  Widget _buildDot(int index) {
    double selectedness = Curves.easeOut.transform(
      max(
        0.0,
        1.0 - ((controller.page ?? controller.initialPage) - index).abs(),
      ),
    );
    double zoom = 1.0 + (_kMaxZoom - 1.0) * selectedness;
    return new Container(
      width: _kDotSpacing,
      child: new Center(
        child: new Material(
          color: color,
          type: MaterialType.circle,
          child: new Container(
            width: _kDotSize * zoom,
            height: _kDotSize * zoom,
            child: new InkWell(
              onTap: () => onPageSelected(index),
            ),
          ),
        ),
      ),
    );
  }

  Widget build(BuildContext context) {
    return new Row(
      mainAxisAlignment: MainAxisAlignment.center,
      children: new List<Widget>.generate(itemCount, _buildDot),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  State createState() => new MyHomePageState();
}

class MyHomePageState extends State<MyHomePage> {

  final _controller = new PageController();

  static const _kDuration = const Duration(milliseconds: 300);

  static const _kCurve = Curves.ease;

  final _kArrowColor = Colors.black.withOpacity(0.8);

  final List<Widget> _pages = <Widget>[
    new ConstrainedBox(
      constraints: const BoxConstraints.expand(),
      child: new FlutterLogo(colors: Colors.blue),
    ),
    new ConstrainedBox(
      constraints: const BoxConstraints.expand(),
      child: new FlutterLogo(style: FlutterLogoStyle.stacked, colors: Colors.red),
    ),
    new ConstrainedBox(
      constraints: const BoxConstraints.expand(),
      child: new FlutterLogo(style: FlutterLogoStyle.horizontal, colors: Colors.green),
    ),
  ];

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      body: new IconTheme(
        data: new IconThemeData(color: _kArrowColor),
        child: new Stack(
          children: <Widget>[
            new PageView.builder(
              physics: new AlwaysScrollableScrollPhysics(),
              controller: _controller,
              itemBuilder: (BuildContext context, int index) {
                return _pages[index % _pages.length];
              },
            ),
            new Positioned(
              bottom: 0.0,
              left: 0.0,
              right: 0.0,
              child: new Container(
                color: Colors.grey[800].withOpacity(0.5),
                padding: const EdgeInsets.all(20.0),
                child: new Center(
                  child: new DotsIndicator(
                    controller: _controller,
                    itemCount: _pages.length,
                    onPageSelected: (int page) {
                      _controller.animateToPage(
                        page,
                        duration: _kDuration,
                        curve: _kCurve,
                      );
                    },
                  ),
                ),
              ),
            ),
          ],
        ),
      ),
    );
  }
}

Is there a way to hide the dots when the keyboard is up? the dots render on top of the keyboard and it looks awful.

Thank you for your great word!

Thank you for the great example!

One small issue I saw was that the dots seem to move while animating. I believe they're moving because the height of the container is changing as the dots are animating smaller/larger. I solved this by setting an explicit height on the dot container:

return new Container(
  width: _kDotSpacing,
  height: _kDotSize * _kMaxZoom,
  ...
)

I also played around with animating the opacity of the dots and this small change enabled that:

child: Material(
  color: Color.fromRGBO(color.red, color.green, color.blue, max(selectedness, 0.5)),
  ...
)

Dot indicator zoom is not working during pageview infinite scroll. Suppose, if I have 3 items in the list and when it scrolls to page 4 (which basically will show page 1) dot indicator is not working. Any workarounds?

You should add itemCount to PageView.builder.

new PageView.builder( itemCount: _pages.length, physics: new AlwaysScrollableScrollPhysics(),

Thanks for the great example!
Was having null safety issues, which I fixed by adding the required modifier before the following parameters:

DotsIndicator({
    required this.controller,
    required this.itemCount,
    required this.onPageSelected,
    this.color: Colors.white,
  }) : super(listenable: controller);

(see https://stackoverflow.com/questions/64560461/the-parameter-cant-have-a-value-of-null-because-of-its-type-in-dart)